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1.
alt
Last visit:
13 years ago
Registered:
14 years ago
2.
The Ultimate Topic List (with Resources, Problems and Templates) This post took $4$ years to make. And this is the most significant thing that I have ever shared in my whole life.
#### Story
Hi, I have been doing CP for like $4$ years and from the very beginning what I have been feeling is a need for a comprehensive topic list that will contain all sorts of topics from easy to advanced with corresponding tutorials, problem lists and templates so that I wouldn't have to look at different sites, from here to there. So what do you do when you think something is missing from the world? Yeah, you create that thing! So here I am, sharing the ultimate topic list that you will need in CP.
When I say that it took me $4$ years to make it, I genuinely mean it. I have been collecting them from the inception of my CP journey and yesterday I thought that it got its almost complete shape. You may not imagine the sheer excitement hidden under each of the characters of this post.
#### Payment
You can pay me just by upvoting this blog and by being a bet...
3.
Codeforces Round #752 #### UPD: (28 April, 2022)
<spoiler summary="Donated Finally">
Details: [here](https://codeforces.com/blog/entry/96333?#comment-907470)
</spoiler>
আবার চলে এসেছি! (That's Bengali for "I am back! (in Terminator mode)")
I am super excited to invite you to participate in [contest:1603] and [contest:1604] which will be held on [contest_time:1604]. This round is rated for both divisions.
You will be given $6$ problems in each division and $2$ hours to solve them. All the problems are authored and prepared by me.
I would like to thank -
- [user:antontrygubO_o,2021-10-26] for his breathtaking(<strike>literally</strike>) coordination of the round. <i style="color:White;"> no funny text this time</i>
- [user:Alpha_Q,2021-10-26], [user:Anachor,2021-10-26] and [user:antontrygubO_o,2021-10-26] for putting up with my dumb ranting and helping with the problems.
- [user:Um_nik,2021-10-26], [user:gamegame,2021-10-26], [user:kefaa2,2021-10-26], [user:dorijanlendvaj,2021-10-26], [u...
">alt, /8771_blobheart.png" width="16px" height="16px" alt="blobheart">. Just hold
right there. The, /assets/emoji/8771_blobheart.png" width="16px" height="16px" alt="blobheart">.
Announcement of Codeforces Round 752 (Div. 1)
Announcement of Codeforces Round 752 (Div. 2)
4.
About Gift Distribution Hello everyone!
<img alt="Packages" src="https://codeforces.com/predownloaded/a7/ce/a7ce52909464af02e2f922990c8c7e4418b98f67.jpg" style="float:right; height: 500px; margin: 10px; max-width:50%;"/>
“My name is Una and I am from the Codeforces team” — this is usually how my messages to users of the site begin. One of the reasons why I write a message is very joyful — sending out gifts to the winners of the competitions and now also to participants of crowdfunding dedicated to the 10th anniversary of Codeforces.
That’s what I’d like to talk about a little bit.
Everyone knows where it all starts — there is a round with gifts, in the comments to which after the ending the coordinators or Mike post a list of winners.
Then, in a short time, all winners receive a system message asking them to update the data about the size of the T-shirt and address. In some special cases, such as crowdfunding, for example, all participants receive an email. For various reasons...
alt="Packages" src="https://codeforces.com/predownloaded/a5/13, alt="Packages" src="https://codeforces.com/predownloaded/a7/ce
5.
(The Ultimate) Code Library Hey everyone, I am sharing my personal code library where I compiled **almost all** the important templates that you will need in CP (saying almost just for courtesy). Most of the codes are originally written by me and some of them are collected from others but modified in a cleaner way. Link: [https://github.com/ShahjalalShohag/code-library](https://github.com/ShahjalalShohag/code-library)
It took me around 4 years to complete the list. Maybe each line is just a line to you but to me it tells a story of the excitements I had while learning those stuffs, the sleepless but fun nights I had to seek knowledge.
###### Why am I sharing this library?
- Just so that your learning path becomes a bit smoother.
- Knowledge hidden inside my head or codes in a private code-library will be useless when I am dead, so it's better to share those among people before I die.
Also, you can make me happy(as in to pay me) just by upvoting this blog and giving a star to the repository.
I beli...
" width="16px" height="16px" alt="blobheart">.
6.
Codeforces Round #741. How contest author is entertaining. Hello, Codeforces! Not too long ago there was my second round, Codeforces #741 (Div. 2). Before it started, I wondered: surely there will be a lot of cheating on my round, just like on any other? So I decided to do something unusual.
As you know from [a blog about cheaters] (https://codeforces.com/blog/entry/93893), it's easy to find telegram/youtube channels with cheaters. So I decided to find a couple and join them...
So, the first telegram group I found was [link not available yet]. There weren't too many cheaters in it but they were, here's an example:
<spoiler summary="Picture">
<a href="https://imgbb.com/"><img src="https://i.ibb.co/kJqMzMS/pic1.png" alt="pic1" border="0"></a>
</spoiler>
I joined this telegram group, and there was a meaningful dialogue:
<spoiler summary="Picture">
<a href="https://ibb.co/1mC2csG"><img src="https://i.ibb.co/VqFB6HY/pic2.png" alt="pic2" border="0"></a>
</spoiler>
This may seem unbelievable, but the admin of the group actuall...
"> alt="pic1" border="0 <https://imgbb.com/>, .png" alt="pic1" border="0"> , .png" alt="pic12" border="0"> , .png" alt="pic3" border="0"> , .png" alt="pic4" border="0"> , .png" alt="pic5" border="0"> , .png" alt="pic6" border="0"> , .png" alt="pic7" border="0"> , .png" alt="pic8" border="0"> , /pic10.png" alt="pic10" border="0"> , /pic11.png" alt="pic11" border="0"> , /pic13.png" alt="pic13" border="0"> , /pic14.png" alt="pic14" border="0"> <https://ibb.co/59C6rJJ>, /pic2.png" alt="pic2" border="0"> , /pic9.png" alt="pic9" border="0">
7.
Codeforces Round #647 — Thanks, Algo Muse! Hello Codeforces!
We have a pleasure to invite you to [Codeforces Round #647 (Div. 1)](https://codeforces.com/contests/1361) and [Codeforces Round #647 (Div. 2)](https://codeforces.com/contests/1362). This round will take place on [contest_time:1361]. In both divisions, you will have **2.5 hours** to solve **6 problems**. Three of them will be shared.
The problems for this round were prepared by [user:MicGor,2020-06-02], [user:Grzmot,2020-06-02], [user:Okrut,2020-06-02] and me.
We would like to thank everyone who made this round possible:
- [user:Nebuchadnezzar,2020-06-02] for the excellent coordination;
- [user:Lewin,2020-06-02], [user:ALILILILILI-KHAN,2020-06-02] for invaluable advice and extensive testing;
- [user:KrK,2020-06-02], [user:yarek,2020-06-02], [user:-is-this-fft-,2020-06-02], [user:w0nsh,2020-06-02], [user:Marckess,2020-06-02], [user:Ari,2020-06-02], [user:Fortin,2020-06-02], [user:Dup4,2020-06-02], [user:kraborak,2020-06-02], [user:300iq,2020-06-02], ...
[user:MikeMirzayanov,2020-06-02]: alt="AlgoMuse"
src="https://codeforces.com/predownloaded/cc/4c, alt="AlgoMuse" src="https://codeforces.com/predownloaded/cc/4c
Announcement of Codeforces Round 647 (Div. 1) - Thanks, Algo Muse!
Announcement of Codeforces Round 647 (Div. 2) - Thanks, Algo Muse!
8.
Ozon Tech Challenge 2020 Hello Codeforces!
<center>
<img alt="ozon" src="https://codeforces.com/predownloaded/6a/99/6a99904b94e5c20a149198e2dde4068dadd9278a.png" style="float:right; height: 200px; margin: 10px; max-width:50%;"/>
</center>
We are glad to invite you to the upcoming “[Ozon Tech Challenge 2020](https://codeforces.com/contests/1305)”, which will start at [contest_time:1305]. The round will be open and rated for everybody!
This round is initiated and supported by Ozon.
Ozon — one of the leading players in e-commerce (provides its customers with over 2.5 million product names in 24 categories), a tech company that actively developing its IT department. They already have the largest Golang team in Russia, a proprietary WMS fulfillment management system completely written by the Ozon team, 250 million lines of logs per day, collected on the site and in the Ozon mobile application. Ozon experts perform at the leading profile conferences GoperCon, Heisenbug, GoWayFest, GolangConf, and also ...
alt="ozon" src="https://codeforces.com/predownloaded/6a/99
9.
think-cell Round 1 Hello, Codeforces!
Welcome to the [contest:1930] supported by think-cell, which will start on [contest_time:1930]. It will be a combined rated round for both divisions.
All problems were authored and prepared by [user:Elegia,2024-02-13] and [user:satyam343,2024-02-07].
We would like to thank:
- [user:errorgorn,2024-02-13] for round coordination and help with preparation
- [user:KAN,2024-02-17] for helping with the preparation of problems
- [user:Alexdat2000,2024-02-13] for Russian translation
- [user:GoatTamer,2024-02-17] and [user:Non-origination,2024-02-17] for discussing problems with us while our proposal was in review and testing the round.
- [user:Kaitokid,2024-02-13], [user:antekb,2024-02-13], [user:vgtcross,2024-02-13], [user:riano_,2024-02-13], [user:mtw,2024-02-13], [user:AboAbdoMC,2024-02-13], [user:Vladithur,2024-02-13], [user:BERNARD,2024-02-13], [user:milind0110,2024-02-13], [user:conqueror_of_tourist,2024-02-13], [user:Um_nik,2024-02-13], [user:gamegame...
/think-cell.svg" align="right" style="height: 100px;" alt="text"/>, ="height: 500px;" alt="text"/>
Announcement of think-cell Round 1
10.
Codeforces Round #932 (Div. 2) <img alt=" " src="https://i.imgur.com/EFlomVE.png" style="float: right;max-width: 100.0%;max-height: 100.0%;width:30%;height:30%">
<h2>Hello, Codeforces! 😇</h2>
------------------
We are glad to invite you to participate in [contest:1935], which will take place at [contest_time:1935] 🔥 😱 🤩
The round has been fully prepared by students of the School CPM 💓 (School of the Pedagogical Skills Center): [user:IzhtskiyTimofey,2024-02-25], [user:AndreyPavlov,2024-02-25], and myself. The theme of all the problems will be our beloved school 😈
This round will be **rated** for participants with a rating below **2100** 😊 Participants with a higher rating can take part out of competition 😋
We would like to thank 💕:
- Our wonderful coordinator [user:Artyom123,2024-02-25] for helping prepare the problems and valuable advice! 😍
- CPM students [user:azureglow,2024-02-25] and [user:max0000561,2024-02-25] ...
alt=" " src="https://i.imgur.com/EFlomVE.png" style="float: right;max-width:
100.0%;max-height
Announcement of Codeforces Round 932 (Div. 2)
11.
Pinely Round 3 (Div. 1 + Div. 2) <img src="https://assets.codeforces.com/images/pinely_logo.png" align="right" style="height: 200px;" alt="text"/>
Ciao, Codeforces! We're glad to invite you to take part in [contest:1909], which will start on [contest_time:1909]. You will be given **9 problems** and **3 hours** to solve them. One of the problems will be divided into two subtasks.
The problems were authored and prepared by me.
<spoiler summary="Spoiler">
</spoiler>
We would like to thank
- [user:errorgorn,2023-12-20] for his fun 🤌 🤡 🤓 😩 coordination;
- [user:Alexdat2000,2023-12-20] for Russian translation;
- [user:franv,2023-12-20] for writing $173$ lines of checker of problem H correctly at the first try;
- [user:franv,2023-12-20] for pictures in the editorial;
- [user:dario2994,2023-12-20], [user:Endagorion,2023-12-20], [user:ffao,2023-12-20], [user:Golovanov399,2023-12-20], [user:nor,2023-12-20] for VIP testing;
- [user:Kaey,202...
;" alt="text"/> Ciao, Codeforces! We're glad to invite you to take part in
[contest:1909], which
Announcement of Pinely Round 3 (Div. 1 + Div. 2)
12.
Codeforces Round #476 (Div. 2) [Thanks, Telegram!] Hi everyone!
<img src="/predownloaded/bf/c1/bfc15c5c56f3e421cc2799e5e1e0273cac1e3605.jpg" alt="digital resistance" title="digital resistance" style="float:right; margin: 0 1em 1em 1em; width:30%"/>
Tomorrow, [on the April 25-th, 2018 at 17:35 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?day=25&month=4&year=2018&hour=20&min=35&sec=0&p1=166) we are holding [contest:965]! The round will be rated for the second division participants, members with higher rating can take part out of competition.
I give the floor to [user:MikeMirzayanov,2018-04-24] to announce the round:
_This round opens a series of thanks-rounds to those who significantly supported Codeforces in the crowdfunding campaign for the 8th anniversary. Although Telegram is not explicitly present on the list of donators, for us this is the first and most important friend. We express our gratitude to Telegram and personally to Pavel Durov for the constant support and send regards from programming contest com...
Hi everyone! alt, alt="digital, Всем привет! alt
Announcement of Codeforces Round 476 (Div. 2) [Thanks, Telegram!]
13.
Petition to revoke unrated account permissions to post comments/blogs Unrated Account Disaster
==================
Recently there have been an obscene number of unrated accounts showing up. Several of them have inappropriate names, so I won't give examples because I want to keep this post clean, but I'm sure you have seen them in the comments. They are likely all by the same individual, possibly with a few copy-cat troublemakers as well.
Recently, certain ones have begun to spam useless comments on old posts to clog up the recent actions, effectively hiding all relevant conversations except on the blog posts they spam on. For whatever reason, these are overwhelmingly on [user:Errichto,2020-07-10]'s old blog posts. Occasionally there are also a flood of obscene blog posts made by the user themselves.
Here's an example of what I mean:
#### This is obnoxious and I would like to see it stop.
The current solution clearly doesn't work. As soon as they get banned or muted or whatever, they c...
problem is that lots of new users have created alt accounts in order to ask
fairly meaningless 'How, A slightly less extreme problem is that lots of new users have created alt
accounts in order to ask
14.
[Tutorial] Common Mistakes in Competitive Programming and How to Avoid Them One thing is for sure. You do make mistakes. I also make miskates and that's what makes us human. But what we can surely do is — to try to minimize the errors that we make throughout our life.
I have compiled some of the mistakes that I made in my early Competitive Programming phase. I also mentioned how to avoid them. Also, in most cases, I will give you a chance to find out what the bug is before I reveal the culprit as I tried to make this blog interactive. The codes that I have used in this blog have been written in C++ as it is the most used language for CP.
**So, if you are new to CP, stick with me as you might don't wanna repeat the mistakes that I made when I was a beginner.**
#### Mistake 1
Check out the following code:
<spoiler summary="Code">
~~~~~
#include<bits/stdc++.h>
using namespace std;
int main() {
int a = 1000'000'000,b = 1000'000'000;
long long product = a * b;
cout << product << '\n';
return 0;
}
~~~~~
</spoiler>
The outp...
://emoji.gg/assets/emoji/8771_blobheart.png" width="16px" height="16px" alt
="blobheart">!
15.
My sad story Teams advancing to 2016 WF Phuket in Asia have been announced recently. This announcement is undisputedly tantamount to a death sentence for me. I am the one waiting anxiously, refresh Dr. Hwang's blog everyday. But it seems that for years, our training was meaningless.
I think many of us dedicate our passion to programming contests because we see them transparent, fair and without any corruption. And I also believe that as contestants, what we should do is only focus on the practice. And I thought those political business should never come to bother me one day. But sadly, it is my team who is going to become one of the sacrifices of a succession of the dissension.
What happened so far
------------------
The quarrel between the Asia director and the local community is [a long story](http://blog.sina.com.cn/s/blog_b946da100101q21y.html) to tell. But it has never been as serious as it was in the past season. Now reflecting on this, I know on the surface everything is going okay...
16.
Codeforces Round #831 (Div. 1 + Div. 2, based on COMPFEST 14 Final) <img alt="logo" src="/predownloaded/03/5f/035ff83d655937b478f5fe9f351f79ac0781f6d2.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Halo, **Codeforces**! 🥰🥰🥰🥰
COMPFEST 14 is happy to invite you to participate in [contest:1740] on [contest_time:1740]. **Note the unusual time of the round**. The round will be **rated for everyone**. You will be given **2 hours and 45 minutes** to solve **9 problems**.
The problems are written by [user:NeoZap,2022-10-26], [user:Nyse,2022-10-26], [user:Pyqe,2022-10-26], and [user:steven.novaryo,2022-10-26].
Scoring distribution: **500 — 1000 — 1500 — 1750 — 2000 — 2500 — 2750 — 3000 — 3500**
We would like to thank:
- [user:KAN,2022-10-26] for helping to host the round;
- [user:errorgorn,2022-10-26] for the based coordination and help with the problem preparation;
- [user:Zappeko,2022-10-26] for helping with the ...
alt="logo"
src="/predownloaded/03/5f/035ff83d655937b478f5fe9f351f79ac0781f6d2.png" style
Announcement of Codeforces Round 831 (Div. 1 + Div. 2)
17.
Codeforces Round #902 (Div. 1, Div. 2, based on COMPFEST 15 — Final Round) <img alt="logo" src="/predownloaded/e3/33/e333915aebea955b43b4ad17845f6dbf58875a0c.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Sugeng enjing, **Codeforces**! 🥰🥰🥰🥰
COMPFEST 15 is happy to invite you to participate in [contest:1876] and [contest:1877] on [contest_time:1876]. Both rounds will be **rated**. You will be given **2 hours and 30 minutes** to solve **7 problems**.
**Note the unusual time of the round**.
------------------
The problems are written by [user:ArvinCiu,2023-10-03], [user:Pyqe,2023-10-03], and [user:nandonathaniel,2023-10-03].
We would like to thank:
- [user:KAN,2023-10-03] for helping to host the round;
- [user:errorgorn,2023-10-03] and [user:ScarletS,2023-10-03] for the based coordination;
- [user:gansixeneh,2023-10-03] and [user:nandonathaniel,2023-10-03] for helping with the problem preparation;
- [user:ArvinCiu,2023-10-03], [user:CyberSleeper,2023-10-03], an...
alt="logo"
src="/predownloaded/e3/33/e333915aebea955b43b4ad17845f6dbf58875a0c.png" style
18.
Where the author of the contest came up entertaining. Cheating cheaters. Hello, Codeforces! A month ago I have wrote [my blog about cheaters](https://codeforces.com/blog/entry/94300). Under that blog, a number of suggestions have accumulated, and there is a number of interesting ideas that could be applied to sabotage a group of cheaters.
I've often seen comments along the lines of:
<spoiler summary="Pictures">.
<a href="https://imgbb.com/"><img src="https://i.ibb.co/r65zfTL/cheat1.png" alt="pic1" border="0"></a>
<a href="https://imgbb.com/"><img src="https://i.ibb.co/Yh6ZfY8/cheat2.png" alt="pic2" border="0"></a>
</spoiler>
Well, doing what [user:Ari,2021-09-28] suggested wasn't really what I wanted to do, but it was worth checking out what would happen if the wrong solutions were sent. I asked some famous user what would happen if I sent the wrong solutions to cheaters. He told me that someone had done this before and that he was quickly debunked.
I wondered whether I could cheat cheaters without getting caught. But for this, I had to do so...
.png" alt="pic1" border="0"> <https://imgbb.com/>, /cheat11.png" alt="pic1" border="0"> , /cheat18.png" alt="pic1" border="0"> , /cheat19.png" alt="pic1" border="0"> , /cheat20.png" alt="pic1" border="0"> , /cheat3.png" alt="pic1" border="0">, alt="pic2" border="0 <https://imgbb.com/>
19.
The 'science' of training in competitive programming So few minutes ago [I answered this question on Quora](https://www.quora.com/What-is-the-best-strategy-to-improve-my-skills-in-Competitive-programming-in-2-3-months/answer/Thanh-Trung-Nguyen). It felt like a good answer (because it has pictures), so I would like to share it again here.
**If you don't see the images, just click the Quora link above**
Many people tell you that solving lots of problems and you will become red on Topcoder/Codeforces one day. It is true, and is the only universally approved way in competitive programming community, but actually it is just half of the story. Let me first explain to you the 'science' of problem solving (which is not very scientific, since it was only developed by myself).
For each problem, in order to solve it, you must jump over a gap. It can be either a difficult implementation, or some hard-to-see observation, or difficult algorithm, etc.
<a href="http://tinypic.com?ref=353d2df" target="_blank"><img src="http://i58.tinypic.com/...
" border="0" alt="Image and video hosting by TinyPic">
20.
Harbour.Space Scholarship Contest 2023-2024 (Div. 1 + Div. 2) Salam, Codeforces! $\color{white}{\text{ «Be attentive about your thought that becomes your behavior» «Be attentive about your behavior that becomes your speech» «Be attentive about your speech because it becomes your habit»«Be attentive about your habit because it becomes your personality»«Be attentive about your personality because it becomes your destiny» Said by: Imam Ali}}$
We're so excited to invite you to take part in our round [contest:1864] which will start on [contest_time:1864]. The round will be **rated and open for everyone**.
The problems were prepared and authored by [user:amenotiomoi,2023-08-19], Dhruvil [user:Psychotic_D,2023-08-19] Kakadiya, Han [user:wuhudsm,2023-08-19] Jinlong, Amir Hossein [user:Amir_Parsa,2023-08-19] Farhadi, Matthew [user:Chromate00,2023-08-19] Roh, [user:JohnVictor,2023-08-19],
[user:odt,2023-08-19], [user:ugly2333,2023-08-19], [user:lavine,2023-08-19], [user:RiverHamster,2023-08-19],
[user:flowerletter,2023-08-19] and [user:Aquamoon...
alt="Codeforces and Harbour.Space" src="/predownloaded/03/fa
Announcement of Harbour.Space Scholarship Contest 2023-2024 (Div. 1 + Div. 2)
21.
Educational Codeforces Round 89 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1366] [contest:1366] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-06-10] Glazov, Adilbek [user:adedalic,2020-06-10] Dalabaev, Vladimir [user:vovuh,2020-06-10] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/22/a2
Announcement of Educational Codeforces Round 89 (Rated for Div. 2)
22.
[Tutorial] The command line: how to read input from file without #ifdef and much more #### Introduction
Instead of algorithms and math, I'll be doing something completely different here.
There is something that has bothered me for a long time: people not understanding
the tools they use to participate in contests and thus failing to take real advantage
of them. And it all goes back to not understanding the command line.
Some of you might say, "well surely, the command line is something obsolete and you're
only clinging to it because you [insert ridiculous amateur-psychology here]?"
No! The command line is not obsolete, and unless competitive programming becomes
so mainstream that software vendors start writing professional-grade tools aimed
specifically at us, it won't be.
[cut]
$~$
What is the command line? Any of these:
As you can see, it comes in many background colors and fonts, but the basic idea
is always the same. It's a box you can type commands in, which it will ...
By `M-x ansi-term`. Or, in normal people' language, by typing Alt-X, then
"ansi-term", then enter.
23.
Pinely Round 1 (Div. 1 + Div. 2) <img align="right" alt="text" src="/predownloaded/1c/91/1c91ed031100f3338aa5f8ed58d0405adb9ff9d7.png" style="height: 500.0px;max-width: 100.0%;max-height: 100.0%;">
Hello, Codeforces!
Members of team EZEC are glad to invite you to participate in **[contest:1761]**, which will start on **[contest_time:1761]**. You will be given **7** problems, **one of which has a subtask**, and **2 hours and 30 minutes** to solve them. The round will be rated for everyone. It is greatly recommended to read all the problems.
There is at least one interactive problem, so please see the [guide of interactive problems](https://codeforces.com/blog/entry/45307) if you are unfamiliar with it.
We would also like to thank:
- Our red sun [user:orzdevinwang,2022-11-19], the youngest TOP10 coder in history, for illuminating our path.
- Our great emperor [user:antontrygubO_o,2022-11-19] for cooperating and coordinating with us to make this round happen. He saved the round by contributing his problem...
alt="text" src="/predownloaded/1c/91/1c91ed031100f3338aa5f8ed58d0405adb9ff9d7
Announcement of Pinely Round 1 (Div. 1 + Div. 2)
24.
Grakn Forces 2020 [Div1 and Div2 combined] Hello, Codeforces!
<center>
<img alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right; height: 50px; margin: 10px; max-width:10%;"/>
</center>
I'm glad to invite you to [contest:1408], which will be held on [contest_time:1408]. It will be **combined rated** round for **both divisions**.
This round is initiated and supported by Grakn Labs. More information you could find [here](https://codeforces.com/blog/entry/82787).
All problems were authored and prepared by [user:300iq,2020-09-29] and [user:isaf27,2020-09-29]. Thanks to [user:growup974,2020-09-29], [user:postscript,2020-09-29], [user:QAQAutoMaton,2020-09-29], [user:PM11,2020-09-29], [user:morzer,2020-09-29], [user:qlf9,2020-09-29], [user:RedDreamer,2020-09-29], [user:gdb_18,2020-09-29], [user:talibmohd,2020-09-29], [user:Dragnoid99,2020-09-29], [user:KAN,2020-09-29] and [user:VladGanzha,2020-09-29] for testing problems and good advice. Thanks to [user:MikeMirzayanov,2020-09-29] for great systems ...
alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right;
height
Announcement of Grakn Forces 2020
25.
Editorial of Codeforces Round #752 Thanks for participating in my contest <a href="https://emoji.gg/emoji/8771_blobheart"><img src="https://emoji.gg/assets/emoji/8771_blobheart.png" width="16px" height="16px" alt="blobheart"></a>. I hope you liked the problems. I would love to hear your feedback in the comments.
If you find anything wrong in the editorial which is more likely to happen because I have written a rather long editorial to make you understand the solutions better, then comment below.
Also, don't forget to upvote to pay for the editorial. See you in my next contest!
[tutorial:1604A]
<spoiler summary="Code">
~~~~~
#include<bits/stdc++.h>
using namespace std;
int main() {
int t; cin >> t;
while (t--) {
int n; cin >> n;
int ans = 0;
for (int i = 1; i <= n; i++) {
int k; cin >> k;
ans = max(ans, k - i);
}
cout << ans << '\n';
}
return 0;
}
~~~~~
</spoiler>
[tutorial:1604B]
<spoiler summary="Code">
~~~~~
#include<bits/stdc++.h>
...
="https://emoji.gg/assets/emoji/8771_blobheart.png" width="16px" height="16px"
alt="blobheart">. I
Tutorial of Codeforces Round 752 (Div. 1)
Tutorial of Codeforces Round 752 (Div. 2)
26.
Codeforces: acm.sgu.ru comes back <img src="/predownloaded/e6/11/e6110c2bbfaa42c460f7c54f681a89fa9fe2395a.png" alt="acmsguru" title="acmsguru" style="float:right; margin: 0 1em 1em 1em;"/>
Hello everyone!
[acm.sgu.ru](http://acm.sgu.ru/) was created ~16 years ago by programming contests participants from Saratov university: [user:MikeMirzayanov,2018-04-23] and [user:andrewlazarev,2018-04-23]. Today its codebase and infrastructure are completely outdated, and supporting it is unreasonably hard. Nonetheless, Codeforces team is regularly asked to revive acmsguru, since there is still a lot of interest in the problemset.
Here is the new functionality in Codeforces — additional section ["acmsguru" in Problemset](/problemsets/acmsguru). All the problems from the old system are moved there. There are still a few things to do here: correctly port interactive problems, improve looks of statements, support the new section in [Codeforces API](/api/help), support adding these problems to mashups.
Anyway, you can ...
alt="acmsguru" title
27.
Educational Codeforces Round 100 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1463] [contest:1463] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-12-16] Glazov, Adilbek [user:adedalic,2020-12-16] Dalabaev, Vladimir [user:vovuh,2020-12-16] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/4d/30
Announcement of Educational Codeforces Round 100 (Rated for Div. 2)
28.
Educational Codeforces Round 88 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1359] [contest:1359] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-05-27] Glazov, Adilbek [user:adedalic,2020-05-27] Dalabaev, Vladimir [user:vovuh,2020-05-27] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/2d/74
Announcement of Educational Codeforces Round 88 (Rated for Div. 2)
29.
Codeforces Round 930 (Div. 1, Div. 2) _"You are braver than you believe, stronger than you seem, and smarter than you think." — A.A. Milne_
Hello Codeforces!
I have the pleasure of inviting you to participate in [contest:1936] and [contest:1937], which will start on [contest_time:1936].
You will be given **6 problems** and **2 hours** to solve them in both divisions.
One of the problems may be **interactive**. So, please refer to the guide on [interactive problems](https://codeforces.com/blog/entry/45307) if you are unfamiliar with them.
The problems were prepared and authored by [user:wuhudsm,2024-02-26], [user:chromate00,2024-02-26], [user:Psychotic_D,2024-02-26] and [user:MagicalFlower,2024-02-26].
We would like to thank :
- [user:irkstepanov,2024-02-26] for coordinating the round;
- [user:BurnedChicken,2024-02-26] for the only <a class="rated-user user-legendary">LGM</a> testing;
- [user:amenotiomoi,2024-02-26],[user:siganai,2024-02-26], [user:vgtcross,2024-02-26], [user:amethyst0,2024-02...
alt
Announcement of Codeforces Round 930 (Div. 1)
Announcement of Codeforces Round 930 (Div. 2)
30.
The Toxic Mindset in Competitive Programming and How to Fight It #### Introduction
Rating is a great measure of skill and a nice way to observe progress by comparing yourself to your past self and seeing where you stand in the community. As great measure as it is, there are a lot of problems that come with it. They have nothing to do with how the rating system works but rather with how human beings function. In this blog post, I will talk about some of the most pressing personal problems that come up with rating and try to provide some advice on how to solve them, speaking from personal experience and from the experience of a lot of other people I know.
#### Associating self-worth to rating
This is, in my opinion, the most significant problem people face, and it also pretty much contains all the following problems as a subset. It's extremely easy to fall into this rabbit hole since, as a competitive programmer, it only feels natural to associate our rating with intelligence and, respectively, our intelligence with self-worth. Why is this su...
31.
Introducing Arugo — A website that provides virtual rating while practicing on problemset Hello Codeforces users.
Today I would like to introduce [Arugo](https://arugo.herokuapp.com/), which is a website that provides virtual rating while practicing on problemset.
On this website, you can practice problems that are suggested through a suggestion system or by your custom choice. Each problem has a window of 80 minutes to solve and if you manage to solve it in time, please validate and you will earn virtual rating. However, if you gave up early or time runs out, you will lose rating eventually. Rating progress will be displayed at the homepage through a graph like in Codeforces and through it, you can visualize your progress and stay motivated to keep going.
<spoiler summary="Rating progress preview">
</spoiler>
<spoiler summary="Challenge preview">
</spoiler>
This site is inspired by my past t...
/emoji/8771_blobheart.png" width="20px" height="20px" alt="blobheart">., ="https://emoji.gg/assets/emoji/8771_blobheart.png" width="20px" height="20px"
alt="blobheart">
32.
Educational Codeforces Round 92 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1389] [contest:1389] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-07-28] Glazov, Adilbek [user:adedalic,2020-07-28] Dalabaev, Vladimir [user:vovuh,2020-07-28] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/0a/83
Announcement of Educational Codeforces Round 92 (Rated for Div. 2)
33.
The 2023 ICPC World Finals Luxor <img src="/predownloaded/60/aa/60aa49ecdb6a668539163c4d7d797ac6f1bb43b3.jpg" align="right" style="height: 350px; margin: 10px 20px 20px;" alt="text"/>
Hello Codeforces!
The 2023 ICPC World Finals Luxor will begin on [April 18, 2024 at 10:00 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=2023+ICPC+World+Finals+Luxor&iso=20240418T12&p1=4626&ah=5). This time, we have a double World Finals. You can distinguish them by colors: blue (fish emoji) and green (crocodile). Join us on the live broadcast for this awesome double event of the year in competitive programming; commentators will include [user:ecnerwala,2024-04-17], [user:SecondThread,2024-04-17], [user:Egor,2024-04-17], and more!
ICPC World Finals Luxor is hosted by The Arab Academy for Science, Technology, & Maritime Transport (AASTMT), the ICPC World Finalist teams for two seasons will compete for World Championship awards, prizes, and bragging rights. More than 130 teams of each season represent the best of gr...
="height: 350px; margin: 10px 20px 20px;" alt="text"/> Hello Codeforces!
34.
Codeforces Round #765. One of the contest authors is entertaining again. Hello, Codeforces! Codeforces #765 (Div. 2) took place not so long ago, and one of its authors was me. When an hour had passed since the contest started, I decided to remember the old days and start making fun of the cheaters.
To that end, I decided to take a look at the old cheater groups and see how they were doing.
The first group I looked into — is the group where the admin is actively fighting against cheaters. So, there really weren't any cheaters on the round. I think that's a success.
The second group I checked out — it's a group with 2.5k users. I decided that just going in there would be too boring, so I decided to write there that I was a contest author. Here's the reaction of the users:
<spoiler summary="Picture">
<a href="https://imgbb.com/"><img src="https://i.ibb.co/0Xt07qt/Screenshot-20220112-164100.png" alt="pic1" border="0"></a>
</spoiler>
Can you imagine?! I write that I am the author of the contest, and I am offered to leak the solution ...
href="https://imgbb.com/">alt, " alt="pic1" border="0"> , /">alt="pic1" border="0"> , ://imgbb.com/">alt="pic1" border="0, ="https://i.ibb.co/0Xt07qt/Screenshot-20220112-164100.png" alt="pic1"
border="0"> , ="https://i.ibb.co/4F3TXNj/Screenshot-20220112-163519.png" alt="pic1"
border="0"> , ="https://i.ibb.co/VNDmzps/Screenshot-20220112-165125.png" alt="pic1"
border="0"> , ="https://imgbb.com/">alt="pic1
35.
Educational Codeforces Round 85 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1334] [contest:1334] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-04-09] Glazov, Adilbek [user:adedalic,2020-04-09] Dalabaev, Vladimir [user:vovuh,2020-04-09] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/82/52
Announcement of Educational Codeforces Round 85 (Rated for Div. 2)
36.
Educational Codeforces Round 110 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1535] [contest:1535] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-06-03] Glazov, Adilbek [user:adedalic,2021-06-03] Dalabaev, Vladimir [user:vovuh,2021-06-03] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/c5/58
Announcement of Educational Codeforces Round 110 (Rated for Div. 2)
37.
Codeforces Round #890 (Div. 2) #####Hi, Codeforces!
[user:Alexdat2000,2023-08-03], [user:Igorfardoc,2023-08-03], and I are pleased to invite you to our [contest:1856], which will be held on [contest_time:1856]. **This round will be rated for participants with a rating lower than 2100.**
We would like to thank:
- [user:errorgorn,2023-08-03] for coordinating the round.
- [user:Yuu,2023-08-03], [user:maomao90,2023-08-03], [user:thenymphsofdelphi,2023-08-03], [user:Dominater069,2023-08-03], [user:Mike4235,2023-08-03], [user:valeriu,2023-08-03], [user:irkstepanov,2023-08-03], [user:zengminghao,2023-08-03], [user:Gheal,2023-08-03], [user:DeMen100ns,2023-08-03], [user:FEDIKUS,2023-08-03], [user:thanhchauns2,2023-08-03], [user:MinaRagy06,2023-08-03], [user:Java,2023-08-03], [user:xudian,2023-08-03], [user:madlogic,2023-08-03], [user:squishybanana04,2023-08-03], [user:stefanbalaz2,2023-08-03], [user:kobebryan9,2023-08-03], [user:Murinh0,2023-08-03], [user:IlyinAD,2023-08-03], [user:Respectively,2023-08-03], [user:p...
alt="CU" src="https://codeforces.com/predownloaded/12/4d
Announcement of Codeforces Round 890 (Div. 2) supported by Constructor Institute
38.
Educational Codeforces Round 163 [Rated for Div. 2] <img alt="Neapolis University Pafos" src="/predownloaded/9a/33/9a332fadbb47050ba9405057df022a6e37eaf5c0.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/>
Hello Codeforces!
We are pleased to announce a new long-term partnership between Codeforces and [Neapolis University Pafos](https://www.nup.ac.cy/). Now educational rounds will be supported by Neapolis University Pafos. Stay tuned and you will find out more soon.
On [contest_time:1948] [contest:1948] will start.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user...
alt="Neapolis University Pafos" src="/predownloaded/9a/33
Announcement of Educational Codeforces Round 163 (Rated for Div. 2)
39.
Educational Codeforces Round 152 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1849] [contest:1849] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours to solve them**.
The problems were invented and prepared by Adilbek [user:adedalic,2023-07-26] Dalabaev, Mikhail [user:awoo,2023-07-26] Piklyaev, Maksim [user:Neon,2023-07-26] Mescheryakov and ...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/2c/74
Announcement of Educational Codeforces Round 152 (Rated for Div. 2)
40.
Educational Codeforces Round 86 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1342] [contest:1342] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-04-25] Glazov, Adilbek [user:adedalic,2020-04-25] Dalabaev, Vladimir [user:vovuh,2020-04-25] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/82/52
Announcement of Educational Codeforces Round 86 (Rated for Div. 2)
41.
This is not an exit. 
I am looking at the post called [*Is Mike Mirzayanov dictator?*](https://codeforces.com/blog/entry/94033) at the moment. I'm reading through the comments, I'm looking at people's reactions, I'm reading Mike's replies, and... I am utterly disappointed.
I demand progress.
For context, I do believe Codeforces is the best website for competitive programming contests at the moment. I sincerely give credit to Mike for creating Codeforces and providing participants and contest authors a platform for interaction completely for free. I am confident that Codeforces is the most appropriate website for being *the* platform for sharing knowledge, exchanging tricks and methods, and collaboration between both contest participants, their authors, and coordinators.
**Please consider this an open letter**, for this is a will not of a single person, but of many individuals. Please consider signing it by stating so in a comment under the...
trip!" alt="xkcd 137: Dreams">
42.
Codeforces Round #861 (Div. 2) <a href="https://ibb.co/hB6SF5F"><img src="https://i.ibb.co/48qHRyR/350-20230320195909.png" alt="350-20230320195909" border="0"></a>
Hello, Codeforces!
I am very glad to invite you to the [Codeforces Round #861 (Div. 2)](https://codeforces.com/contest/1808), which will take place in [contest_time:1808]. <b>This round will be rated for the participants with rating lower than 2100.</b>
My sincere thanks to:
- [user:KAN,2023-03-26] и [user:aleks5d,2023-03-26] for the great coordination of this round!
- [user:Wind_Eagle,2023-03-26], [user:BaluconisTima,2023-03-26], [user:kartel,2023-03-26], [user:gepardo,2023-03-26] and [user:244mhq,2023-03-26] for the tasks ideas, and also [user:BaluconisTima,2023-03-26], [user:244mhq,2023-03-26], [user:VEGAnn,2023-03-26], [user:Vladik,2023-03-26] and [user:andrew,2023-03-26] for preparing the tasks.
- [user:vilcheuski,2023-03-26] and [user:programmer228,2023-03-26] the rest of the author team, without whom this round would not have happ...
alt <https://ibb.co/hB6SF5F>
Announcement of Codeforces Round 861 (Div. 2)
43.
This one weird trick will speed up your I/O 5x Just do this!!
```cpp
#include <iostream>
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
// Your code here
int n;
std::cin >> n;
long long sum = 0;
for (int i = 0; i < n; i++) {
int x;
std::cin >> x;
sum += x;
}
std::cout << sum << std::endl;
}
```
This will speed up your code so much you won't have to care about spending time in I/O anymore!! Give likez plz :3
[cut]
<!-- -->
---
Yeah, no. That's not how it works. We're still using `<iostream>`, and that means we have to rely on virtual inheritance and all the deoptimizations that follow from that. Even if you use a random "here's-my-fast-io-library" snippet from Codeforces, you still depend on block-buffered output. (Also, none of those libraries mesh well with floats.) In many cases, more CPU time is spent encoding/decoding numbers than interacting with the file system.
Can we do better? ...Yeah, stupid que...
alt
44.
Educational Codeforces Round 115 [Rated for Div.2] Hello Codeforces!
On [contest_time:1598] [contest:1598] will start. **Note that the start time is unusual**.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Alex [user:fcspartakm,2021-10-09] Frolov, Mikhail [user:awoo,2021-10-09] Piklyaev, Max [...
alt="Codeforces and Harbour.Space" src="/predownloaded/bf/50
Announcement of Educational Codeforces Round 115 (Rated for Div. 2)
45.
Educational Codeforces Round 111 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1550] [contest:1550] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2021-07-13] Dalabaev, Vladimir [user:vovuh,2021-07-13] Petrov, Ivan [user:BledDest,2021-07-13] Androsov, Mak...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/a3/89
Announcement of Educational Codeforces Round 111 (Rated for Div. 2)
46.
Educational Codeforces Round 151 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1845] [contest:1845] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-06-28] Dalabaev, Ivan [user:BledDest,2023-06-28] Androsov, Maksim [user:Neon,2023-06-28] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/51/24
Announcement of Educational Codeforces Round 151 (Rated for Div. 2)
47.
Educational Codeforces Round 155 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1879] [contest:1879] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-09-23] Dalabaev, Ivan [user:BledDest,2023-09-23] Androsov, Maksim [user:Neon,2023-09-23] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/6e/6a
Announcement of Educational Codeforces Round 155 (Rated for Div. 2)
48.
Educational Codeforces Round 108 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1519] [contest:1519] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-04-28] Glazov, Adilbek [user:adedalic,2021-04-28] Dalabaev, Vladimir [user:vovuh,2021-04-28] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/60/71, alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/70/30
Announcement of Educational Codeforces Round 108 (Rated for Div. 2)
49.
Educational Codeforces Round 143 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1795] [contest:1795] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-02-15] Dalabaev, Vladimir [user:vovuh,2023-02-15] Petrov, Ivan [user:BledDest,2023-02-15] Androsov, Ma...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/13/dc
Announcement of Educational Codeforces Round 143 (Rated for Div. 2)
50.
Educational Codeforces Round 145 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1809] [contest:1809] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-03-19] Dalabaev, Ivan [user:BledDest,2023-03-19] Androsov, Maksim [user:Neon,2023-03-19] Mescheryakov ...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/eb/05
Announcement of Educational Codeforces Round 145 (Rated for Div. 2)
51.
COMPFEST 13 Finals Mirror (Unrated, ICPC Rules, Teams Preferred) <img alt="logo" src="/predownloaded/31/e8/31e886f0ba055023282a2f68b4b254d98c02c727.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Hi <strong><span style="color:#bfac00;">Code</span><span style="color:#006fbf;">for</span><span style="color:#b00000;">ces</span></strong> ଘ(੭*ˊᵕˋ)੭* ੈ♡‧₊˚!
We're delighted to invite you to [COMPFEST 13 — Finals Online Mirror (Unrated, ICPC Rules, Teams Preferred)](https://codeforces.com/contests/1575) on <a class="contest-time" contestid=1575></a>.
All problems were written and prepared by [user:hocky,2021-09-18], [user:steven.novaryo,2021-09-18], [user:rama_pang,2021-09-18], [user:JulianFernando,2021-09-18], [user:Zap,2021-09-18], [user:Panji,2021-09-24], [user:richiesenlia,2021-09-24], [user:Sakamoto,2021-09-24], and [user:Markus_geger,2021-09-24].
I would also like to thank:
- [user:KAN,2021-09-18] for helping to host the mirror round;
- ([user:AVM.Martin,2021-09-30], [user:Ace_02,202...
alt="logo"
src="/predownloaded/31/e8/31e886f0ba055023282a2f68b4b254d98c02c727.png" style
52.
COMPFEST 15 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred) <img alt="logo" src="/predownloaded/54/ec/54ec8a2a974eb225636db378f5470e039144d49b.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Hello, **Codeforces**! 😍😍
We are happy to invite you to participate in [COMPFEST 15 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred)](https://codeforces.com/contests/1866) on <a class="contest-time" contestid=1866></a>. COMPFEST is a national **ICPC-style contest** for university students in Indonesia.
The problems are written and prepared by [user:ArvinCiu,2023-08-30], [user:asteriskzie,2023-08-30], [user:CyberSleeper,2023-08-30], [user:Edbert.H,2023-08-30], [user:FreeJinG,2023-08-30], [user:gansixeneh,2023-08-30], [user:KokiCoder,2023-08-30], [user:nandonathaniel,2023-08-30], and [user:Pyqe,2023-08-30].
We would also like to thank:
- [user:KAN,2023-08-30] for helping to host the mirror round;
- [user:AMnu,2023-08-30], ([user:KerakTelor,2023-08-30], [user:Owmic...
alt="logo"
src="/predownloaded/54/ec/54ec8a2a974eb225636db378f5470e039144d49b.png" style
53.
A Beautiful Technique for Some XOR Related Problems ## Inspiration
I'm very excited about this blog, as it took me quite a lot of effort and scavenging through the internet to completely grasp the concept of this technique(That's probably because I have almost zero knowledge in Linear Algebra or I'm just plain dumb). So I feel like I genuinely conquered a challenge, and I really want to share it with someone. But there's no way my CP friends circle will believe it, they'll think I'm just trying to show off :P
So here I am, sharing it on CF. I also created a [personal blog](https://drschwad.github.io/), so that if I ever feel like sharing something again(not only about CP), I can write a blog there. I also added this same post [there](https://drschwad.github.io/2019-08-06-z2-space-xor-trick/), you can read it there if you prefer dark theme. I'll be pleased to hear any thoughts on the blog or if I can improve it in some way ^\_^
## Introduction
Since it concerns Linear Algebra, there needs to be a lot of formal stuff going on ...
54.
Codeforces Round #843. One of the contests authors decided to entertain again Hello, Codeforces! Codeforces #843 (Div. 2) round took place not so long ago, and I was one of its authors. When an hour had passed since the contest had started, I (you could say, by tradition) decided to enter the groups with cheaters and make fun of them once again.
And one more thing before we begin. [user:peltorator,2023-01-08] has launched a cool blog contest, I encourage everyone to participate: [blog](https://codeforces.com/blog/entry/110840).
Next. [user:COOLMAARK,2023-01-13], thanks for writing about the cheaters group, but it was better to do it not in the comments to the announcement, for not to advertise the group.
<spoiler summary="Comment under blog">
<a href="https://ibb.co/WtS5ZYz"><img src="https://i.ibb.co/NSwC5HN/pic1.png" alt="pic1" border="0"></a>
</spoiler>
Now to the point. So, since some cheaters recognize me, I invited [user:try_kuhn,2023-01-08] to help. In all the past cases, there was a problem: yes, sure, cheaters would submit the bad code, bu...
href="https://ibb.co/vPWMP0c">alt="pic7" border="0, src="https://i.ibb.co/vmzBGB8/pic16.png" alt="pic16" border="0"> , ">alt="pic11" border="0"> , ">alt="pic12" border="0"> , /5YGHmxR/pic4.png" alt="pic4" border="0"> <https://ibb.co/Tk2p5r3>, /CsPVwyz">alt="pic28" border="0"> , /G2XqMwF/pic33.png" alt="pic33" border="0"> , /NSwC5HN/pic1.png" alt="pic1" border="0"> , /frGSStP/pic32.png" alt="pic32" border="0"> , /pic14.png" alt="pic14" border="0"> , /pic2.png" alt="pic2" border="0"> , /pic3.png" alt="pic3" border="0"> , /pic31.png" alt="pic31" border="0"> , /r2D3Qkr/pic20.png" alt="pic20" border="0"> <https://ibb.co/Gxm1Yg3>, ://i.ibb.co/0BqRMpg/pic13.png" alt="pic13" border="0"> , ://i.ibb.co/MM7qq4G/pic12.png" alt="pic12" border="0"> , ://i.ibb.co/kg9Lw8k/pic27.png" alt="pic27" border="0"> , ://i.ibb.co/pvhkfS5/pic30.png" alt="pic30" border="0"> , ://i.ibb.co/vmzBGB8/pic16.png" alt="pic16" border="0"> <https://ibb.co/3rcYRX8>, ://ibb.co/WtS5ZYz">alt="pic1" border="0">, ://ibb.co/vPWMP0c">alt="pic7" border="0"> , ://imgbb.com/">alt="pic15" border="0"> , ="https://i.ibb.co/HdRjcbM/pic10.png" alt="pic10" border="0"> , ="https://i.ibb.co/r2D3Qkr/pic20.png" alt="pic20" border="0">
55.
Polynomial Round 2022 (Div. 1 + Div. 2, Rated, Prizes!) Hello, Codeforces!
<img alt="Polynomial" src="https://codeforces.com/predownloaded/31/39/3139af7f9a6628da7d4b7ce4353a192cf59ee3f5.png" style="float:right;height: 250px; margin: 10px; max-width:50%;"/>
Winter holiday is coming! And we are excited to invite you to our third round, [contest:1774], which will be held on [contest_time:1774]. You are given **8 problems** and **2.5 hours** to solve them.
All problems were written and prepared by [user:Ecrade_,2022-12-14], [user:Little09,2022-12-14], [user:ChthollyNotaSeniorious,2022-12-14], [user:DataStructures,2022-12-14], [user:Cirno_9baka,2022-12-14], [user:mejiamejia,2022-12-14] and me.
And thanks to [user:dorijanlendvaj,2022-12-14], [user:gisp_zjz,2022-12-14], [user:gamegame,2022-12-14], [user:triple__a,2022-12-14], [user:Chenyu_Qiu,2022-12-14], [user:Suiseiseki,2022-07-25], [user:q-w-q-w-q,2022-12-14], [user:leukocyte,2022-12-14], [user:waaitg,2022-12-14], [user:Kubic,2022-12-14], [user:LHQing,2022-12-14], [user:zrmpaul...
alt="Polynomial" src="https://codeforces.com/predownloaded/31/39
Announcement of Polynomial Round 2022 (Div. 1 + Div. 2, Rated, Prizes!)
56.
Codeforces: Results of 2013 Hello! Do you feel the breath of New Year?
<img src="http://assets.codeforces.com/images/tree.png" style="float:right;margin: 0 1em 1em 1em;"/>
The clock shows a day before New Year, so it is time to sum up the past. I do not have speech-writers for words in the style of
"what recently seemed almost impossible, it becomes a fact of life" so I'll be short. Thank you all! Your unfading interest and
constant help inspire Codeforces team for new achievements! Brilliant writers, invisible soldiers: testers, tireless and greedy
for knowledge participants — all of you help Codeforces do better!
I've dug into the records and made a partial list of the most notable major improvements of 2013. Some large improvements of our
infrastructure are not in the list, as the community can not see them directly.
* A simple way to add contest from [Polygon](https://polygon.codeforces.com/) to Codeforces::Gym.
* Drafts embedded in text form fields in Codeforces and Polygon.
* Multipl...
alt
57.
Educational Codeforces Round 150 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1841] [contest:1841] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-06-11] Dalabaev, Ivan [user:BledDest,2023-06-11] Androsov, Maksim [user:Neon,2023-06-11] Mesche...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/ba/b2
Announcement of Educational Codeforces Round 150 (Rated for Div. 2)
58.
Educational Codeforces Round 142 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1792] [contest:1792] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-01-23] Dalabaev, Vladimir [user:vovuh,2023-01-23] Petrov, Ivan [user:BledDest,2023-01-23] Androsov, Ma...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/30/fc
Announcement of Educational Codeforces Round 142 (Rated for Div. 2)
59.
Educational Codeforces Round 147 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1821] [contest:1821] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-04-19] Dalabaev, Ivan [user:BledDest,2023-04-19] Androsov, Maksim [user:Neon,2023-04-19] Mesche...
alt="Harbour.Space" src="https://mirror.codeforces.com/predownloaded/4a/65
Announcement of Educational Codeforces Round 147 (Rated for Div. 2)
60.
Educational Codeforces Round 131 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1701] [contest:1701] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-07-07] Dalabaev, Vladimir [user:vovuh,2022-07-07] Petrov, Ivan [user:BledDest,2022-07-07] Androsov, Mak...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/b5/f0, alt="Harbour.Space" src="https://codeforces.com/predownloaded/df/b7, Также от наших друзей и партнёров из Harbour.Space есть сообщение для вас: alt
="Harbour.Space
Announcement of Educational Codeforces Round 131 (Rated for Div. 2)
61.
Codeforces Round #862 (Div. 2) Hello, everyone at Codeforces.com!
In this round, I ([user:Alexdat2000,2023-04-01]) and two of my friends — [user:FairyWinx,2023-04-01] and [user:Sevlll777,2022-06-03] — prepared **6 problems** for you (one of which is divided into two subtasks), and you will have **2 hours** to solve them. Everyone is welcome to follow the link: [contest:1805] at [contest_time:1805]. **This round will be rated for all participants with a rating of strictly less than 2100.**
And now a few acknowledgements:
- Thanks to [**<font color="#ff0000">[Coordinator] pashka</font>**](https://codeforces.com/profile/pashka) for coordinating and helping with testers
- Special thanks to [**<font color="#ff0000">[G.O.A.T.] Mangooste</font>**](https://codeforces.com/profile/Mangooste) for discussing tasks and testing
- Thanks to all the testers:
[**<font color="#000000">[MVP</font><font color="#ff0000">++</font><font color="#000000">] Ormlis</font>**](https://codeforces.com/profile/Ormlis...
" alt="China" title="China"> [user:b6e3,2023-04-02] 6 6987 , -flag" src="https://cdn.codeforces.com/s/80272/images/flags-16/cn.png" alt
="China" title="China, /80272/images/flags-16/cn.png" alt="China" title="China">
[user:amiya,2023-04-02] 7, /80272/images/flags-16/us.png" alt="USA" title="USA">
[user:Geothermal,2023-04-02] 0:02, /images/flags-16/us.png" alt="USA" title="USA"> [user:Geothermal,2023-04-02]
0:02 , ://cdn.codeforces.com/s/80272/images/flags-16/cn.png" alt="China"
title="China"> [user:amiya,2023-04-02], ://cdn.codeforces.com/s/80272/images/flags-16/cn.png" alt="China"
title="China"> [user:b6e3,2023-04-02]
Announcement of Codeforces Round 862 (Div. 2)
62.
ICPC World Finals Moscow <img src="/predownloaded/a2/a3/a2a35281876bb89fc2558c46e36184124ca60caf.png" align="right" style="height: 400px; margin: 10px 20px 20px;" alt="text"/>
Hello, Codeforces!
ICPC World Finals Moscow will begin on [October 5, 2021 at 8:30 (UTC+3)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICPC+World+Finals+Moscow&iso=20211005T0830&p1=166&ah=5). We are thrilled to invite you to join the live broadcast of the main event of the year in the world of sports programming!
For the very first time in October 2021, Moscow will host the world’s most prestigious competition for young IT talents, the ICPC World Finals Championship. The last International Collegiate Programming Contest has hosted over 60000 students
from 3,514 universities in 115 countries that span the globe. October 5 more than 100 teams will compete in logic, mental speed, and strategic thinking at Russia’s main Manege Central Conference Hall.
Some useful links:
- [Official website of the ICPC](http://...
="height: 400px; margin: 10px 20px 20px;" alt="text"/>
63.
[Tutorial] Fully Dynamic Trees Supporting Path/Subtree Aggregates and Lazy Path/Subtree Updates Hey everyone! Usually when I post stuff on CF I just drop an external link to my blog, but this time I would like to also paste the same content natively on CF to see if it leads to more engagement. You can read the exact same article on my blog [here](https://mzhang2021.github.io/cp-blog/ds5/).
Also, special thanks to [user:alien_lover,2022-06-10] and [user:gabrielwu,2022-06-10] for proofreading.
---
## Motivation
We will solve **[this problem](https://dmoj.ca/problem/ds5)**.
## Prologue
The original name of this problem is [SONE1](https://darkbzoj.cc/problem/3153), originating from the fiery depths of Chinese OI. Amazingly, the Chinese have figured out how to augment the link/cut tree to solve this problem (ref [1](https://www.cnblogs.com/clrs97/p/4403244.html), [2](https://blog.csdn.net/iamzky/article/details/43494481)). Maintaining subtree aggregates with a LCT isn't difficult, and there's a well-known [Codeforces article](https://codeforces.com/blog/entry/67637) ...
alt="Image 1"/>, alt="Image 2"/>, alt="Image 3"/>, alt="Image 4" width
64.
A List of Useful Equations in Competitive Programming Hi, I am super excited to be back with another list. This time it is a **collection of some useful equations in Competitive Programming**.
### Motivation
Do you find it bad if you couldn’t solve a problem just because you didn’t know about a certain equation?
Do you find it difficult to take a quick look at an equation that you know exists but forgot about it while solving a problem?
Do you think that all the equations that are important in CP are just cluttered and you are too lazy to collect them in one place?
Well, then you are in the right place! I am here to solve all of the aforementioned problems. I believe you should not waste your precious time searching the internet for important equations. You should solve more problems. I am here to undertake the nasty task of collecting things.
### Payment
Everything comes with a cost. You need to do something for me. That is you need to upvote this blog. Pretty easy!
### Acknowledgement
Thanks to the following guys ...
/8771_blobheart.png" width="16px" height="16px" alt="blobheart">.
65.
Codeforces Round #843 (Div. 2) <a href="https://ibb.co/whxngNB"><img src="https://i.ibb.co/1GwCQf7/38-20230104210158.png" alt="38-20230104210158" border="0"></a>
Hello, Codeforces!
I am very glad to invite you to the [Codeforces Round #843 (Div. 2)](https://codeforces.com/contest/1775), which will take place in [contest_time:1775]. <b>This round will be rated for the participants with rating lower than 2100.</b>
My sincere thanks to:
- [user:KAN,2023-01-08] и [user:aleks5d,2023-01-08] for the great coordination of this round!
- [user:Wind_Eagle,2023-01-08], [user:BaluconisTima,2023-01-08], [user:kartel,2023-01-08] и [user:aleks5d,2023-01-08] for the tasks ideas, and also [user:Wind_Eagle,2023-01-08], [user:BaluconisTima,2023-01-08], [user:kartel,2023-01-08], [user:VEGAnn,2023-01-08] и [user:Vladik,2023-01-08] for preparing the tasks.
- [user:andrew,2023-01-08], [user:gepardo,2023-01-08], [user:244mhq,2023-01-08], [user:vilcheuski,2023-01-08] the rest of the author team, without whom this round woul...
alt="38 <https://ibb.co/whxngNB>
Announcement of Codeforces Round 843 (Div. 2)
66.
Educational Codeforces Round 109 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1525] [contest:1525] will start. **Please, note the unusual start time.**
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-05-15] Glazov, Adilbek [user:adedalic,2021-05-15] Dalabaev, Vladimir...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/e8/5b
Announcement of Educational Codeforces Round 109 (Rated for Div. 2)
67.
Codeforces Deltix Round Summer 2021 [Div.1 + Div.2] <a href="https://deltix.io/"><img alt="deltix" src="https://assets.codeforces.com/images/deltix/EcCsUtwbu1yq6Av.gif" style="float:right; height: 400px"/></a>
<p>Hi <span style="font-weight:bold">Code</span><span style="color:rgb(71,94,152);font-weight:bold">forces</span>!</p>
We are **[DELTIX](https://deltix.io/)**. Founded in 2005, DELTIX is one of the market leaders in software development for financial research and products for systematic and algorithmic trading. In 2020 DELTIX joined the EPAM family. Our mission is to turn promising ideas into breakthrough products fast.
We are experts in:
* aggregation, storage, and processing large volumes of time-series data
* data modeling
* testing and deployment of quantitative models
In our team we value such skills as:
* knowledge of algorithms
* high-performance coding
* low latency data streams processing
We are excited to announce that one of our products [TimeBase Community Edition](https://github.com/finos/...
alt="deltix" src="https://assets.codeforces.com/images/deltix
<https://deltix.io/>
68.
Educational Codeforces Round 119 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1620] [contest:1620] will start. **Please, note the unusual start time.**
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2021-12-17] Dalabaev, Vladimir [user:vovuh,2021-12-17] Petrov, Ivan...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/31/5c, alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/ca/7c
Announcement of Educational Codeforces Round 119 (Rated for Div. 2)
69.
Educational Codeforces Round 107 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1511] [contest:1511] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-04-11] Glazov, Adilbek [user:adedalic,2021-04-11] Dalabaev, Vladimir [user:vovuh,2021-04-11] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/6f/69, alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/bb/2f, alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/e4/b4
Announcement of Educational Codeforces Round 107 (Rated for Div. 2)
70.
Educational Codeforces Round 123 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1644] [contest:1644] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-02-21] Dalabaev, Vladimir [user:vovuh,2022-02-21] Petrov, Ivan [user:BledDest,2022-02-21] Androsov, Mak...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/53/0d
Announcement of Educational Codeforces Round 123 (Rated for Div. 2)
71.
Educational Codeforces Round 112 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1555] [contest:1555] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2021-07-29] Dalabaev, Vladimir [user:vovuh,2021-07-29] Petrov, Ivan [user:BledDest,2021-07-29] Androsov, Mak...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/d7/d0
Announcement of Educational Codeforces Round 112 (Rated for Div. 2)
72.
Codeforces Round #689 (Div. 2), based on Zed Code Competition 2020 <img alt="epam" src="https://d3373sevsv1jc.cloudfront.net/uploads/communities_production/page_part/46738/50534DE5F997443DBE1BBA96BC394F66.png" style="float:right; height: 200px; "/>
<p>Hi <span style="font-weight:bold">Code</span><span style="color:rgb(71,94,152);font-weight:bold">forces</span>!</p>
I am glad to announce and invite you to [contest:1461], which will be held on [contest_time:1461].
We want to offer you to solve 6 problems taken from the Zed Code Competition 2020, which was held as part of the [Adapt by Zed](http://zed.epam.com/) conference powered by [EPAM Systems](https://www.epam.com/).
**This round will be rated for the participants with rating lower than 2100.**
- The authors of the round are: Aliaksandr [user:AleXman111,2020-12-10] Kryvasheyeu, Aliaksandr [user:sdryapko,2020-12-10] Drapko, Aliaksei [user:netman,2020-12-10] Vistiazh and me.
- The round was coordinated by Vladimir [user:vovuh,2020-12-10] Petrov and Nikolay [user:KAN,2020-12-10] Kalini...
alt="epam"
src="https://d3373sevsv1jc.cloudfront.net/uploads/communities_production/page_part
Announcement of Codeforces Round 689 (Div. 2, based on Zed Code Competition)
73.
Codeforces Round #675 (Div. 2) based on Qualification Andersen Programming Contest 2020 Tryam, Codeforces!
<img alt="andersen" src="https://user-images.githubusercontent.com/1968460/94995698-b4bf1b80-05a8-11eb-8206-05370556b080.jpg" style="float:right; height: 200px; "/>
Perhaps you are waiting for us to announce the final of BSUIR championship, but for now we are only glad to invite you to [contest:1422], which will be held on [contest_time:1422]. **This round will be rated for the participants with rating lower than 2100.**
The problems were prepared for you by [user:andrew,2020-10-03], [user:hloya_ygrt,2020-10-03], [user:AleXman111,2020-10-03] and [user:Vladik,2020-10-03] together with me. We think that we have prepared good problems for [contest:297213]. After that we selected the best ones for this round.
The company [Andersen](https://contest.andersenlab.com/) has been holding a competition for the second year already, which is primarily intended to support students of regional universities in Belarus and Ukraine (starting this year).
First of all, we...
alt="andersen"
src="https://user-images.githubusercontent.com/1968460/94995698-b4bf1b80-05a8
Announcement of Codeforces Round 675 (Div. 2)
74.
ICPC World Finals Dhaka — Live Broadcast and Mirror! Hello, Codeforces!
<img alt="ICPC World Finals Dhaka Logo" src="/predownloaded/34/3e/343e3d2ae8f44d7c5225d52db21632db4bec56fe.svg" style="height: 300.0px;max-width: 100.0%;max-height: 100.0%;" align="right">
The ICPC World Finals Dhaka will begin on [November 10, 2022 at 11:00 (UTC+6)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICPC+World+Finals+Dhaka&iso=20221110T11&p1=73&ah=5). This is the culmination of the 2020-2021 ICPC season, and we have over 130 teams competing for the title of ICPC champion. Please join us on the live broadcast for the main event of the year in competitive programming; commentators will include [user:ecnerwala,2022-11-09], [user:SecondThread,2022-11-09], [user:Egor,2022-11-09], and more! There will also be a live mirror for you to solve the problems alongside the contestants!
Some useful links:
* [ICPC Homepage](https://icpc.global/)
* [World Finals Homepage](https://worldfinals.icpc.global/)
* [World Finals Schedule](https://docs....
alt="ICPC World Finals Dhaka Logo" src="/predownloaded/34/3e
75.
Educational Codeforces Round 134 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1721] [contest:1721] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-08-26] Dalabaev, Vladimir [user:vovuh,2022-08-26] Petrov, Ivan [user:BledDest,2022-08-26] Androsov, Mak...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/76/a2
Announcement of Educational Codeforces Round 134 (Rated for Div. 2)
76.
[Tutorial] Invariants and Monovariants Hello Codeforces! Some months ago I wrote tutorial about [basics of recurrent sequences](http://codeforces.com/blog/entry/54154). This blog, my second tutorial is about mine another favorite topic — Invariants and Monovariants. These are useful concepts which will help you solving problems, especially, constructive ones. Even if you are not familiar with this topics, I'm sure that you solved problems with use of invariants and monovariants without knowing it, continue reading, you will understand my point :) There will be hard problems which are based on old IMO problems, so I will try my best to explain solutions of examples.
So, what are Invariants and Monovariants? An invariant is a quantity that doesn't change. A monovariant is a quantity that changes monotically (that is, non-decreasing or non-increasing). Seems simple, yes?
Let's start with a few easy examples which you will better understand its point. I suggest you to try solving problems by your own before reading ...
alt="image" border="0">, alt="tut1" border="0">, alt="tut2" border="0">
77.
Educational Codeforces Round 128 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1680] [contest:1680] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-05-12] Dalabaev, Vladimir [user:vovuh,2022-05-12] Petrov, Ivan [user:BledDest,2022-05-12] Androsov, Mak...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/5c/f1, alt="Harbour.Space" src="https://codeforces.com/predownloaded/83/24
Announcement of Educational Codeforces Round 128 (Rated for Div. 2)
78.
Editorial for Codeforces Round #919 (Div. 2) ##Information about the round
<spoiler summary="Rating predictions (inspired by BucketPotato's editorial)">
| Person | A | B | C | D | E | F1 | F2 |
|--------------------------------------------|------|------|------|------|------|------|------|
| [user:sum,2024-01-13] | 800 | 1300 | 1500 | 1900 | 2000 | 2200 | 2900 |
| [user:oursaco,2024-01-13] | 800 | 1100 | 1300 | 1600 | 1800 | 2100 | 3100 |
| [user:omeganot,2024-01-13] | 900 | 1000 | 1400 | 1700 | 1900 | 2200 | 2800 |
| [user:sriniv,2024-01-13] | | | | 1900 | 2000 | 1900 | |
| [user:apple_method,2024-01-13] | 1000 | 1200 | 1400 | 1900 | 1600 | | |
| [user:awesomeguy856,2024-01-13] | 800 | 1100 | 1400 | 1800 | 1900 | 2000 | 2800 |
| [user:nonrice,2024-01-13] | 900 | 1000 | 1400 | 1750 | | | |
| [user:null_aw...
" alt="Image for observation" style="height: 8cm; width: auto;">
Tutorial of Codeforces Round 919 (Div. 2)
79.
Educational Codeforces Round 104 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1487] [contest:1487] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-02-14] Glazov, Adilbek [user:adedalic,2021-02-14] Dalabaev, Vladimir [user:vovuh,2021-02-14] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/82/52
Announcement of Educational Codeforces Round 104 (Rated for Div. 2)
80.
Codeforces Round #848 (Div. 2) Hello, Codeforces!
[user:adnan_toky,2023-01-23] and I are super thrilled to invite everyone to participate in [contest:1778], which will be held on [contest_time:1778].
This round is rated for the participants with ratings strictly **lower than 2100**. You will be given **6 problems** and **2 hours** to solve them. All the problems are authored and prepared by [user:adnan_toky,2023-01-25] and me. To get the 6 problems approved, we needed to propose 12 problems in total <a href="https://emoji.gg/emoji/6390-sneaky-wink-catto"><img src="https://cdn3.emoji.gg/emojis/6390-sneaky-wink-catto.png" width="16px" height="16px" alt="sneaky_wink_catto"></a>.
**UPD:** Score distribution: $500-1000-1250-1750-2250-2750$
We would like to thank:
- [user:darkkcyan,2022-02-12] for incredible coordination and help with the problem preparation
- [user:Alexdat2000,2022-07-16] for the Russian translations and precious help regarding the statements and limits
- [user:KAN,2023-01-30] for upgrad...
/6390-sneaky-wink-catto.png" width="16px" height="16px" alt="sneaky_wink_catto">
., /9131-king">alt
Announcement of Codeforces Round 848 (Div. 2)
81.
Educational Codeforces Round 76 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1257] [contest:1257] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2019-10-23] Glazov, Adilbek [user:adedalic,2019-10-23] Dalabaev, Vladimir [user:Vovuh,2019-10-23] Petrov, Ivan [user:Bl...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/76/9b
Announcement of Educational Codeforces Round 76 (Rated for Div. 2)
82.
Educational Codeforces Round 80 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1288] [contest:1288] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-01-13] Glazov, Adilbek [user:adedalic,2020-01-13] Dalabaev, Vladimir [user:Vovuh,2020-01-13] Petrov, Ivan [user:Bl...
alt="Hello Muscat" src="https://codeforces.com/predownloaded/be/34
Announcement of Educational Codeforces Round 80 (Rated for Div. 2)
83.
Educational Codeforces Round 130 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1697] [contest:1697] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-06-11] Dalabaev, Vladimir [user:vovuh,2022-06-11] Petrov, Ivan [user:BledDest,2022-06-11] Androsov, Mak...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/3c/16, alt="Harbour.Space" src="https://codeforces.com/predownloaded/59/28, Также от наших друзей и партнёров из Harbour.Space есть сообщение для вас: alt
="Harbour.Space
Announcement of Educational Codeforces Round 130 (Rated for Div. 2)
84.
Codeforces Round #678 (Div. 2) based on Final Andersen Programming Contest 2020 <img alt="andersen" src="https://user-images.githubusercontent.com/1968460/94995698-b4bf1b80-05a8-11eb-8206-05370556b080.jpg" style="float:right; height: 200px; "/>
<p>Hi <span style="font-weight:bold">Code</span><span style="color:rgb(71,94,152);font-weight:bold">forces</span>!</p>
I am glad to announce and invite you to [contest:1436], which will be held on [contest_time:1436]. A couple of weeks ago, we held [contest:1422] based on the tasks of the [contest:297213], and this time we want to offer you to solve the best 5-6 problems of the finals.
**Please note the unusual start time of the round. This round will be rated for the participants with rating lower than 2100.**
This is the second year that [Andersen](https://contest.andersenlab.com/) has been holding the competition, which is primarily intended to support students of regional Universities in Belarus and Ukraine (starting this year). This year, [60 students](http://apc2020.contest.codeforces.com/group/vBi1GNDIyR...
alt="andersen"
src="https://user-images.githubusercontent.com/1968460/94995698-b4bf1b80-05a8
Announcement of Codeforces Round 678 (Div. 2)
85.
I want to propose a feature regarding alt accounts / multi accounts **Why add anything?**
My current problem is that alt accounts mess up the rating system and rankings in the lower divisions.
**My solution:**
People create alt accounts for certain reasons. I would like to propose a feature that gives people **an alternative to regular alt accounts**. I don't want to take away alt accounts, I want to improve the experience in a meaningful way.
**Why do people participate in contests with alt accounts?**
- self assurance that their real rating is justified
- desire to participate in low Division contests as real as possible
- desire to chase a positive feedback loop (dopamine kicks)
- desire to start a new account, because the main account is hardstuck/peaked
- desire to participate in lower Division hacking
- …
**My solution in details:**
Allow people to create and manage fairAlt accounts through their main account settings.
**a fairAlt (basic):**
- can be created with 1 button click
- starts at 0 rating
- can gain ra...
I want to propose a feature regarding alt accounts / multi accounts, activity of the main account. - when creating an account, one receives a
notification that hiddenalt, **Why add anything?** My current problem is that alt accounts mess up the
rating system and, **Why do people participate in contests with alt accounts?**, I assume that the more advantages a fairAlt has over a normal alt, the more
people will use this, I enjoy using alt accounts in games, but I would not use one on Codeforces
because it is bad, My current problem is that alt accounts mess up the rating system and rankings
in the lower, People create alt accounts for certain reasons. I would like to propose a
feature that gives people
86.
Your true self **TL;DR stop making new accounts just to post blogs and post it on your main.**
Hello everyone!
I know it has been a while since I ever post a blog. I'm lazy ok? Today I want to tell you what went pretty bad recently: The existence of **alts**.
There are many type of alts which is being used for different stuffs, but let's put it in a side and talk about the most annoying type for me. Yeah, those unrated alts that appears everywhere, from recent blogs to comment sections.
If I am not wrong then every 1-2 days there would be an alt like that appear and post something like: Asking to be better at topics, talking about CP in india, or other stuffs. But what occur the most? Those who "catch" cheaters.
When **EVERY SINGLE CONTEST** that ends there would appear a blog that says "Cheater EXPOSED in Codeforces round #XYZ!" or "Google Kickstart round M code LEAKED!" from a random alt created shortly ago, drop a bunch of comments, and then some continue doing their "good" ...
Codeforces round #XYZ!" or "Google Kickstart round M code LEAKED!" from a
randomalt created shortly, am not wrong then every 1-2 days there would be an alt like that appear and
post something like, If I am not wrong then every 1-2 days there would be an alt like that appear
and post something
87.
[Tutorial] Intuition on Slope Trick # Introduction
As mentioned in my previous blog, I will be writing a tutorial about slope trick. Since there are already many blogs that goes through the concept of slope trick, my blog will focus more on the intuition behind coming up with the slope trick algorithm.
Hence, if you do not know slope trick yet, I suggest that you read other slope trick blogs such as https://codeforces.com/blog/entry/47821 and https://codeforces.com/blog/entry/77298 before reading my blog. In the future explanation on the example problems, I will assume that the reader already knows the big idea behind slope trick but do not know how to motivate the solution.
Great thanks to [user:errorgorn,2022-06-25] for proofreading and writing the section on convex convolution and merchant otter.
# When to use slope trick?
Most of the time, slope trick can be used to optimise dp functions in the form of $dp_{i, j} = \min(dp_{i - 1, j - 1}, dp_{i - 1, j} + A_i)$ or dp functions containing costs with abs...
" alt="Image of dp[2] pasted 3 times to form dp[3]" width="50%" style="float:
left"/>
88.
Harbour.Space Scholarship Contest 2023-2024 (Div. 1 + Div. 2) Editorial Thank you for participation and we hope you enjoy this round ヽ(^ o ^)/.
During the contest, there was a small issue in problem D. For those affected, we have skipped your duplicate submissions (if your duplicate submissions were not skipped, please let us know). We apologize again for any inconvenience caused.
In addition, we are honored to invite you to our unofficial round tomorrow (*╹▽╹*) [Invitation to TheForces Round #22 (Interesting-Forces)](https://mirror.codeforces.com/blog/entry/119771)
### [1864A-Increasing and Decreasing](https://mirror.codeforces.com/contest/1864/problem/A)
Idea : [user:wuhudsm,2023-08-27]
<spoiler summary="Tutorial">
We use the following greedy construction:
For all $i$ ($1<i<n$), set $a_i=a_{i+1}-(n-i)$. If $a_2-a_1 \geq n-1$, we've found a solution, otherwise there is no solution.
Proof. Assume there's a solution which includes an index $i$ ($1<i<n$) such that $a_{i+1}-a_i>n-i$. We can make $a_j:=a_j+\Delta$ for all $j$ ($2 \le j ...
alt="Editoral_img1.png" title, alt="Editorial_img2.png" title, alt="Editorial_img3.jpg" title
89.
Educational Codeforces Round 154 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1861] [contest:1861] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-08-30] Dalabaev, Ivan [user:BledDest,2023-08-30] Androsov, Maksim [user:Neon,2023-08-30] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/24/9f
Announcement of Educational Codeforces Round 154 (Rated for Div. 2)
90.
Educational Codeforces Round 157 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1895] [contest:1895] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-11-02] Dalabaev, Ivan [user:BledDest,2023-11-02] Androsov, Maksim [user:Neon,2023-11-02] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/55/e6
Announcement of Educational Codeforces Round 157 (Rated for Div. 2)
91.
Educational Codeforces Round 132 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1709] [contest:1709] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2022-07-20] Dalabaev, Vladimir [user:vovuh,2022-07-20] Petrov, Ivan [user:BledDest,2022-07-20] Androsov, Mak...
Our friends at Harbour.Space also have a message for you: alt="Harbour.Space"
src="https, Также от наших друзей и партнёров из Harbour.Space есть сообщение для вас: alt
="Harbour.Space
Announcement of Educational Codeforces Round 132 (Rated for Div. 2)
92.
Educational Codeforces Round 156 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1886] [contest:1886] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-10-08] Dalabaev, Ivan [user:BledDest,2023-10-08] Androsov, Maksim [user:Neon,2023-10-08] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/04/c8
Announcement of Educational Codeforces Round 156 (Rated for Div. 2)
93.
[Tutorial] XOR Segment Tree hi
Today's post continues my theme of niche but sometimes useful topics in CP. This idea was brought to my attention by [user:magnus.hegdahl,2022-08-07], so thanks to him!
### General Description
The motivation behind the technique is to solve the following problem:
Given a static array $a$ of $n$ elements (for convenience, I'll assume $n$ is a power of $2$, if not, the array can be padded with null elements), answer $q$ queries of the form $($$l$, $r$, $x$$)$ where you have to print $\sum\limits_{k = l}^r a_{k \oplus x}$. In particular, a query where $x = 0$ is just a normal segtree query. If $x$ is non-zero, the array indices that are being queried are no longer contiguous, making this impossible to solve with a normal segtree. Note: the only requirement is that the "addition" operation is associative (commutativity is not required). The solution provided in this blog solves the problem in $\mathcal{O}(n \log{} n + q \log{} n)$ with $\mathcal{O}(n \log{} n)$ memory. The mem...
alt="segtree-image-good" border="0">
94.
Invitation to NUS CS3233 Final Team Contest 2023 Mirror <img alt="logo" src="/predownloaded/7a/2d/7a2da3823042e763e0d15d6571ba0bcb38139f90.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Hello, Codeforces community!
We are happy to invite you to participate in [National University of Singapore (NUS) CS3233 Final Team Contest 2023 Mirror](https://codeforces.com/contestInvitation/3d3b392eb92ff65022128f4e22462d5eaff55a25) on [Monday, April 10, 2023, at 09:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=10&month=4&year=2023&hour=12&min=35&sec=0&p1=166). CS3233 is a course offered by NUS to prepare students in competitive problem solving.
The contest is unofficial and will be held in Codeforces Gym. Standard ICPC rules **(Unrated, ICPC Rules, Teams Preferred)** apply. **The contest is unrated**. **Note the unusual starting time**.
The problems are written and prepared by [user:user202729_,2023-04-08], [user:rama_pang,2023-04-08], and [user:pooty,2023-04-08].
We wo...
alt="logo"
src="/predownloaded/7a/2d/7a2da3823042e763e0d15d6571ba0bcb38139f90.png" style
95.
ICPC 2023 Online Challenge powered by Huawei <img src="/predownloaded/60/ed/60eddb18a54159e57dd1ffc836857f58420039bf.jpg" align="right" style="height: 280px;" alt="text"/>
#### Hello, Codeforces!
From the ICPC 2023 World Finals, we are happy to bring you an exciting online event:
**The ICPC 2023 Online Challenge powered by Huawei**，which will start on November 20, 2023 15:00 UTC (UTC+8)
In this Challenge, you will have a unique chance:
- to **compete with top programmers globally**
- to **solve 1 exciting problem** prepared by Huawei
- to **win amazing prizes** from Huawei!
**It is an individual competition.**
#### The ICPC 2023 Online Challenge powered by Huawei:
**Start:** [November 20, 2023 15:00 (UTC+8)](https://www.timeanddate.com/worldclock/fixedtime.html?day=20&month=11&year=2023&hour=10&min=0&sec=0&p1=166)
**Finish:** [December 4, 2023 15:00 (UTC+8)](https://www.timeanddate.com/worldclock/fixedtime.html?day=04&month=12&year=2023&hour=10&min=0&sec=0&p1=166)
**We hope you'll enjoy this ...
="height: 280px;" alt="text"/>
Announcement of ICPC 2023 Online Challenge powered by Huawei
96.
Serious Altitude Issue in IOI 2025 Hello, CodeForces!
Today, I would like to discuss about an issue of IOI 2025 venue.
The venue of IOI 2025 is still not officially announced, but according to [the website](https://ioi2025.bo/), IOI 2025 will be held in La Paz, Bolivia.
<img src="https://i.ibb.co/PFjkSF1/1.png" alt="1" border="0" width="40%"></img>
As you know, La Paz is one of the highest cities in the world. For example, the center of La Paz is at 3600 meters above the sea level, and [El Alto International Airport](https://en.wikipedia.org/wiki/El_Alto_International_Airport), which is the nearest large airport from La Paz, is at 4100 meters above the sea level. Therefore, **altitude sickness can be a big concern.** I think that even the following things can happen:
* 20% of the contestants collapsed at the airport, and they were even unable to reach hotels
* 30% of the contestants collapsed during hotel stay, opening ceremony, practice sessions and excursions, and they were unable to participate in the c...
alt="1" border="0" width="40%">
97.
Educational Codeforces Round 106 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1499] [contest:1499] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-03-17] Glazov, Adilbek [user:adedalic,2021-03-17] Dalabaev, Vladimir [user:vovuh,2021-03-17] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/70/4c, alt="Harbour.Space" src="https://codeforces.com/predownloaded/44/96
Announcement of Educational Codeforces Round 106 (Rated for Div. 2)
98.
Educational Codeforces Round 82 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1303] [contest:1303] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-02-11] Glazov, Adilbek [user:adedalic,2020-02-11] Dalabaev, Vladimir [user:Vovuh,2020-02-11] Petrov, Ivan [user:Bl...
alt="Hello Muscat" src="https://codeforces.com/predownloaded/39/43
Announcement of Educational Codeforces Round 82 (Rated for Div. 2)
99.
Hack me! (CF Round #262) Hey, I wanted to start new series about hacking. I think that this part of programming contests is really underrated, but can be helpful for both people solving problems (you should know what tricky cases you need to consider) and people writing problems (you should know how to write nice tests covering everything).
So in this series, which I will try to continue, I will talk over hacks at Codeforces Rounds. I will try to do some statistics and take a look at most common mistakes in passing contests.
It is my first article related to hacking (and first at all :)), so feel free to suggest something, correct me on some errors or mistakes (my English still can be much better :))
and tell about your hacks. Thanks in advance!
So let's move to [contest:460].
**Update:** added country wise statistics (at the end).
**Update:** added chart with hacks over time and first hacks.
**Update:** the handles are now full of colours, with many thanks to awesome [user:sylap97,2014-08-2...
/entry/13469#comment-183941">here): alt="Here should be graph" src="http, And my graph showing hacks over time: alt="Here should be graph" src="http
100.
Educational Codeforces Round 77 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1260] [contest:1260] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 problems** and **2 hours** to solve them.
The problems were invented and prepared by ZiXuan Yan [user:RDDCCD,2019-11-26], Roman [user:Roms,2019-11-26] Glazov, Adilbek [user:adedalic,2019-11-26] Dalabaev, Vladimir [user:Vo...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/76/9b
Announcement of Educational Codeforces Round 77 (Rated for Div. 2)
101.
Educational Codeforces Round 141 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1783] [contest:1783] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-01-07] Dalabaev, Vladimir [user:vovuh,2023-01-07] Petrov, Ivan [user:BledDest,2023-01-07] Androsov, Ma...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/30/fc
Announcement of Educational Codeforces Round 141 (Rated for Div. 2)
102.
ACM ICPC 2016−2017, Northeastern European Regional Contest Hello, Codeforces.
This weekend ITMO University in St. Petersburg with Barnaul, Almaty and Tbilisi will host ACM ICPC Northeastern European Regional Contest. <img src="http://codeforces.com/predownloaded/44/32/443202c5ba097f921d78177380c4048617e14d18.jpg" align="right" style="height: 280px; margin: 20px;" alt="text"/>
We have [266 teams](http://neerc.snarknews.info/index.cgi?data=macros/players&menu=index&head=index&qf=neerc&class=neerc2016&year=2016&sort1=5d&sort2=6d&sort3=7d&order5=y&order6=y&hide9=y) (thanks to [user:MikeMirzayanov,2016-12-02] and [user:snarknews,2016-12-02] for the link) competing for the chance to go to the ACM ICPC World Finals 2017 which is going to take place in South Dakota, USA.
In ITMO University site 106 teams will compete, including [ACM ICPC 2016 World Champions](https://icpc.baylor.edu/community/world-finals-champions) and the team that is leading [Opencup ranklist](http://opencup.ru/index.cgi?data=macros/results&menu=index&head=index&ncup=och&c...
/443202c5ba097f921d78177380c4048617e14d18.jpg" align="right" style="height:
280px; margin: 20px;"alt="text"/>
103.
Educational Codeforces Round 105 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1494] [contest:1494] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2021-03-01] Glazov, Adilbek [user:adedalic,2021-03-01] Dalabaev, Vladimir [user:vovuh,2021-03-01] Petrov, Ivan [us...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/5a/65, alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/cc/1a
Announcement of Educational Codeforces Round 105 (Rated for Div. 2)
104.
Codeforces Round #615 (Div. 3) <almost-copy-pasted-part>
Hello!
[contest:1294] will start at [contest_time:1294]. You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.
The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.
You will be given 6 or 7 (or 8) problems and 2 hours to solve them.
Note that **the penalty** for the wrong submission in this round (and the following Div. 3 rounds) is **10 minutes**.
[Remember] (/blog/entry/59228) that only the <i>trusted participants of the third division</i> will be included in the ...
alt="Hello Muscat" src="https://codeforces.com/predownloaded/be/34
Announcement of Codeforces Round 615 (Div. 3)
105.
SIT STAR Contest <b><i>Hello!</i></b>
<b><i>Together with colleagues [Schaffhausen Institute of Technology](https://sit.org/) we hold such an event. If you want to study in Switzerland, then perhaps this is your chance!</i></b>
<b><i>— Mike</i></b>
Hello, Codeforces!
<center>
<img alt="SIT" src="https://static.tildacdn.com/tild6536-6661-4864-b937-393639346635/sit_logo_black_short.svg" style="float:right; height: 200px; margin: 10px; max-width:50%;"/>
</center>
We are thrilled to announce a new SIT STAR Contest by the [Schaffhausen Institute of Technology in Switzerland](https://sit.org/). The winners will have a chance to get a fully-funded Master’s scholarship in Computer Science and Software Engineering.
**<font color="red">What is the SIT STAR Contest?</font>**
The goal of the SIT STAR Contest is to promote interest in the field of Computer Science and Software Engineering, give students an opportunity to demonstrate their knowledge of programming, and be considered for...
alt="SIT" src="https://static.tildacdn.com/tild6536-6661-4864-b937-393639346635
106.
Educational Codeforces Round 148 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1832] [contest:1832] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-05-11] Dalabaev, Ivan [user:BledDest,2023-05-11] Androsov, Maksim [user:Neon,2023-05-11] Mesche...
alt="Harbour.Space" src="https://mirror.codeforces.com/predownloaded/39/4d
Announcement of Educational Codeforces Round 148 (Rated for Div. 2)
107.
Инструкция к CHelper <div><div><b>1. Установка</b></div><div>Надо скачать <a href="http://code.google.com/p/idea-chelper/downloads/detail?name=chelper2.4.jar">файл плагина</a> и <a href="http://code.google.com/p/idea-chelper/downloads/detail?name=chelper.properties">файл конфигурации</a>. Файл плагина надо положить в %home_dir%\\.IntelliJIdea10\\config\\plugins (если папки plugins нету --- создать ее), а так же добавить в качестве библиотеки к модулям своего проекта (делается через Project Structure -> Dependencies -> Add Single Entry Module Library...). Затем поправить конфигурацию согласно своим нуждам, положить ее в корень проекта --- и все, можно использовать. Для работы с TopCoder необходим плагин moj для арены, инструкции и ссылка --- <a href="http://apps.topcoder.com/forums/;jsessionid=84612D3FBAD554FF37DD381DD857BC20?module=Thread&threadID=597911&start=0&mc=60">здесь</a>, инструкция на русском --- <a href="http://habrahabr.ru/blogs/sport_programming/120942/">здесь</a></div><div><i...
Tests (Alt+F5) --- opens test editor, Archive Task (Alt+F6) --- удаляет задание, сохраняя код в archiveDirectory и,
если, Copy Source (Alt+F8) --- копирует содержимое Main.java в буфер обмена. Полезно
для, Edit Tests (Alt+F5) --- открывает редактор тестов (в том числе для TopCoder), New Task (Alt+F2) --- создает новое задание в defaultDirectory и выбирает его в
108.
Yandex.Algorithm 2017, third elimination round: editorial (with challenges, bells and whistles) This time I've decided to play with spoilers to faciliate the presentation as some of the guys here did before. Tell me what you think about this write-up!
#### Problem A. Shifts
Topics: dynamic programming.
Summary: the first "hard" problem of the contest. Knowing your basic DP problems helps a lot, but coming up with the precisely correct solution may take a lot of persistence.
Solution: Suppose that we are allowed to make left circular shifts as well as right ones.
<spoiler summary="Can you solve the problem in this case?">
First of all, making a shift is effectively moving a character to a different position in the string. Clearly, moving a character more than once makes no sense since we could have just moved it to its final destination instead without wasting any operations. Also, it obvious that the number of occurences of each character should be the same in both strings since it is preserved by shifts.
Now, consider the characters that are *not* moved by ...
109.
Educational Codeforces Round 78 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1278] [contest:1278] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2019-12-18] Glazov, Adilbek [user:adedalic,2019-12-18] Dalabaev, Vladimir [user:Vovuh,2019-12-18] Petrov, Ivan [user:Bl...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/89/06
Announcement of Educational Codeforces Round 78 (Rated for Div. 2)
110.
COMPFEST 14 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred) <img alt="logo" src="/predownloaded/03/5f/035ff83d655937b478f5fe9f351f79ac0781f6d2.png" style="float: right;height: 100.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
Hello, **Codeforces**! 🤗
We are happy to invite you to participate in [COMPFEST 14 Preliminary Online Mirror (Unrated, ICPC Rules, Teams Preferred)](https://codeforces.com/contests/1725) on <a class="contest-time" contestid=1725></a>. COMPFEST is a national **ICPC-style contest** for university students in Indonesia.
The problems are written and prepared by [user:Pyqe,2022-09-02], [user:steven.novaryo,2022-09-02], [user:Nyse,2022-09-02], [user:muhammadhasan01,2022-09-02], [user:gansus,2022-09-02], [user:nandonathaniel,2022-09-02], [user:FerdiHS,2022-09-02], [user:TakeMe,2022-09-02], and [user:NeoZap,2022-09-02].
We would also like to thank:
- [user:KAN,2022-09-02] for helping to host the mirror round;
- rama_pang ([user:rama_pang,2022-09-02], [user:zappeko,2022-09-02], [user:Berted,202...
alt="logo"
src="/predownloaded/03/5f/035ff83d655937b478f5fe9f351f79ac0781f6d2.png" style
111.
Educational Codeforces Round 153 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1860] [contest:1860] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="https://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-08-15] Dalabaev, Ivan [user:BledDest,2023-08-15] Androsov, Maksim [user:Neon,2023-08-15] Mesch...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/ac/89
Announcement of Educational Codeforces Round 153 (Rated for Div. 2)
112.
Invitation for ICPC Indonesia COMPFEST 12 Multi-Provincial Contest Online Mirror Hello Codeforces Community. I would like to invite you all for [ICPC Indonesia COMPFEST 12 Multi-Provincial Contest Online Mirror](https://codeforces.com/contests/1425). I am the Person In Charge of the event.
<img alt="compfestlogo" src="/predownloaded/88/b0/88b08f638596aeda8840ec8d7e5dd9944c17286a.jpg" style="float: right;height: 200.0px;margin: 10.0px;max-width: 100.0%;max-height: 100.0%;">
I want to thank:
- Faculty of Computer Science, The University of Indonesia, for providing guidance and support for the official event.
- Our committee: [user:hocky,2020-09-24], [user:julianfernando,2020-09-24], [user:faustaadp,2020-09-24], [user:dewa251202,2020-09-24], [user:MIsForMiracle,2020-09-24], [user:faishol27,2020-09-24].
- Our testers: [user:AMnu,2020-09-24], [user:stevenwjy,2020-09-24], [user:Yehezkiel,2020-09-24]
- [user:MikeMirzayanov,2020-09-24]: for giving us the opportunity to host this online mirror. Also, for Codeforces and Polygon platform.
The online mir...
alt="compfestlogo"
src="/predownloaded/88/b0/88b08f638596aeda8840ec8d7e5dd9944c17286a.jpg
113.
Grakn Forces 2020 “Codeforces… assemble!”
<center>
<img alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right; height: 50px; margin: 10px; max-width:10%;"/>
</center>
We are thrilled to announce **Grakn Forces 2020**; hosted by Codeforces and sponsored by [Grakn Labs](https://vaticle.com/). Thank you to Codeforces for providing a world-class competition structure to partner with. We can’t wait to see what you all are capable of. This international competition consists of 1 round, lasting 2.5 hours. The contest will comprise 7-9 problems and will be in accordance with classic Codeforces rules.
**Prizes:**
- 1st place = 500 euros
- 2nd place = 250 euros
- 3rd place = 100 euros
**Additional Prizes:**
Top 50 receive:
_Grakn Labs swag pack:_
- Stickers
- Grakn Labs t-shirt
Random 50 from 51-250 receive:
_Grakn Labs swag pack:_
- Stickers
- Grakn Labs t-shirt
**About Grakn Labs**
[Grakn Labs](https://github.com/graknlabs) is a team...
alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right;
height
Announcement of Grakn Forces 2020
114.
VNOI Cup 2022 Round 1 [Mirror invitation] Hello Codeforces!
<!-- Short sentence for invitation -->
We are glad to invite you to take part in mirror round of [the first round of VNOI Cup](https://oj.vnoi.info/contest/vnoicup22_r1_mirror), which will take place [at 13:00 UTC, on this Saturday, 18th June](https://www.timeanddate.com/worldclock/fixedtime.html?msg=%5BMirror%5D%20VNOI%20Cup%202022%20-%20Round%201&iso=2022-06-18T13:00:00), and it is hosted on our builtin platform — [VNOJ](https://oj.vnoi.info/)!
<center>
<img src="/predownloaded/5a/27/5a27775a5a9c31eea4eb942d31bdd4ade1ef35e7.png" alt="round1-poster" />
</center>
<!-- Ask qualified participants to take part in the official round -->
**If you are Vietnamese and _qualified_ according to these rules mentioned on [this post](https://cup.vnoi.info/rule/)**, please consider taking part in [the official round](https://oj.vnoi.info/contest/vnoicup22_r1)!
<!-- Introduce VNOI -->
VNOI Cup is a Competitive Programming competition held by VNOI (Vietnam Oly...
alt="round1
115.
Register for the Montgomery Blair Informatics Tournament (mBIT) 2020 Fall Round! If you are interested in participating in the **Montgomery Blair Informatics Tournament (mBIT)**, which will be held online from [12:00-4:00 PM EST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Montgomery+Blair+Informatics+Tournament+%28mBIT%29+Fall+2020+Round&iso=20201114T12&p1=263&ah=4) on **Saturday, November 14 (11/14/20)**, please register at https://mbit.mbhs.edu/. The contest will be hosted on our personal servers at https://mbit.live/. All problems were written by the [Montgomery Blair HS Computer Team](https://codeforces.com/ratings/organization/2457), including [user:12tqian,2020-10-28], [user:gabrielwu,2020-10-28], [user:galen_colin,2020-10-28], [user:smax,2020-10-28], [user:meiron03,2020-10-28], [user:Blastman,2020-10-28], [user:czhang2718,2020-10-28], and [user:csytrn,2020-10-28]. Special thanks to [user:balbit,2020-11-12] for spending hours test solving our hardest problems!
mBIT is split into two divisions: **Standard** and **Advanced**. Teams may choose ...
/logosb996403a2cdde30a.png" alt="logosb996403a2cdde30a.png" border="0" />, alt="mbit_fall_poster.png
116.
Looking for developers willing to build a simulated codeforces stock exchange. Hello Competitors!
I'm looking to build a simulated exchange with intrinsic value based on codeforces rating, taking inspirations from the problems and solutions from real-world exchanges.
If you're interested in financial markets and you want to gain a better understanding of the kind of work they do there, this is an easy project to work on to get a ground-up understanding of markets and trading.
You're not required to have any previous financial background. You need to have an interest in learning and enjoy finding and critiquing different solutions to interesting mathematical problems. I recommend applying irrespective of your experience level, I believe there is a lot to learn in the development of a trading system.
I'm looking for 10-15 people to fill 3 types of roles(closed).
#### Stock Exchange Developer
You will develop the back end orderbooks to keep track of all orders and fill them as fast and efficiently as possible. You will learn about the actual i...
117.
Educational Codeforces Round 160 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1913] [contest:1913] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours to solve them**.
The problems were invented and prepared by Adilbek [user:adedalic,2023-12-17] Dalabaev, Mikhail [user:awoo,2023-12-17] Piklyaev, Maksim [user:Neon,2023-12-17] Mescheryakov, Rom...
alt="Harbour.Space" src="/predownloaded/af/83
Announcement of Educational Codeforces Round 160 (Rated for Div. 2)
118.
2020 ICPC Graph Mining Challenge — Powered by Huawei: Battle of the Connected Brains [<img src="/predownloaded/aa/57/aa577c257884a5ae68792513c31d9f64fd7bff5f.png" align="right" style="height: 300px; margin: 10px 30px 20px;" alt="text"/>](https://challenge.icpc.global/)
**UPD:** You can predownload tests as an encrypted zip-archive by the links https://test1.codeforces.com/icpc-challenge-2020-tests.zip or https://test4.codeforces.com/icpc-challenge-2020-tests.zip (~80MB). The password is `64e00d81811bbc463e1e636af`.
Hello everyone!
<a href="https://u.icpc.global/" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(207, 56, 34);color: white;">Live broadcast</a>
Announcing the **ICPC Graph Mining Challenge**, Powered by Huawei and brought to you by [ICPC U](https://u.icpc.global/). Graphs are a powerful mechanism for representing many aspects of our daily lives, from mobile call routing to disease tracking. Answering various graph-related questions enables solutions to some of the most challenging, modern problems. The ICPC Challenge prese...
="height: 300px; margin: 10px 30px 20px;" alt
="text"/>](https://challenge.icpc.global/)
Announcement of ICPC Challenge 2020: Practice
Announcement of ICPC Challenge 2020
119.
Atcoder Beginner Contest 174 — Unofficial English Editorial Hi all, [Atcoder Beginner Contest 174](https://atcoder.jp/contests/abc174) was today. I wrote an unofficial English editorial. Hope it helps!
### [A: Air Conditioner](https://atcoder.jp/contests/abc174/tasks/abc174_a)
We simply write an if statement.
Runtime: $\mathcal{O}(1)$.
<spoiler summary="Sample code">
~~~~~
int x = in.nextInt();
out.println(x >= 30 ? "Yes" : "No");
~~~~~
</spoiler>
### [B: Distance](https://atcoder.jp/contests/abc174/tasks/abc174_b)
We can loop through all the points, and test each one. To avoid potential rounding errors, it's simplest to check $x^2 + y^2 \le D^2$, so we can keep everything in integers.
Runtime: $\mathcal{O}(N)$.
<spoiler summary="Sample code">
~~~~~
int n = in.nextInt();
long d = in.nextInt();
d = d * d;
Point[] points = Point.readPoints(in, n);
int answer = 0;
for (Point p : points) {
if (p.x * p.x + p.y * p.y <= d)
answer++;
}
out.println(answer);
~~~~~
</spoiler>
### [C: Repsept](h...
120.
[Rated, Prizes!] DYTECHLAB Cup 2022 Round Announcement [Div.1 + Div.2] <img src="/predownloaded/ff/85/ff85322f740c69d9497bd061c096bad892766f13.png" align="right" style="height: 400px;" alt="text"/>
> Hello Codeforces. Hoping you're having a wonderful day! ^_^
# DYTECHLAB Cup 2022
This October, we invite you to the **first ever [contest:1737]** that will start on [contest_time:1737]. The problems were prepared by members of our company who _share a passion for Competitive Programming_. It is an open and rated round for both divisions.
The round will consist of **7 problems** and will be **150 minutes** long. We wish everyone good luck and have a positive delta!
### Prizes
- 1st place: **US$200** cash prize
- 2nd place: **US$100** cash prize
- 3rd place: **US$50** cash prize
Also, we understand that contestants like dope **MERCHANDISE**, so we are giving away lots of them!
- **Top 20** will get a merchandise package which will include: a t-shirt **with your Codeforces handle on it**, a notebook, 2 pens, and a sports bag.
- **3...
="height: 250px;" alt="text"/> , ="height: 300px;margin:10px" alt="text"/>, ="height: 400px;" alt="text"/>
Announcement of Dytechlab Cup 2022
121.
Educational Codeforces Round 164 [Rated for Div. 2] <img alt="Neapolis University Pafos" src="/predownloaded/9a/33/9a332fadbb47050ba9405057df022a6e37eaf5c0.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/>
Hello Codeforces!
The series of Educational Rounds continues thanks to the support of the [Neapolis University Pafos](https://www.nup.ac.cy/).
On [contest_time:1954] [contest:1954] will start.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2024-04-11] Dalabaev, Ivan [user:BledDest,2024-04-11] Androsov, Maksim [user:Neon,2024-04-11] Mescheryakov, Rom...
alt="Neapolis University Pafos" src="/predownloaded/9a/33
Announcement of Educational Codeforces Round 164 (Rated for Div. 2)
122.
Educational Codeforces Round 81 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1295] [contest:1295] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-01-13] Glazov, Adilbek [user:adedalic,2020-01-13] Dalabaev, Vladimir [user:Vovuh,2020-01-13] Petrov, Ivan [user:Bl...
alt="Hello Muscat" src="https://codeforces.com/predownloaded/39/43
Announcement of Educational Codeforces Round 81 (Rated for Div. 2)
123.
AlgoWiki: A wiki dedicated to competitive programming <img align="right" src="https://wiki.algo.is/img/logo.png" alt="AlgoWiki logo" />
Hi everyone. Over the past couple of years I've been collecting problems,
articles, and competitive programming resources that I find interesting. It's
already grown to dozens of sheets in multiple Google Sheet documents, and is a
pretty bad mess. As an effort to organize this list and make it public, I
decided to turn it into an online wiki dedicated to competitive programming:
[AlgoWiki](https://wiki.algo.is/).
The url is **wiki.algo.is**, so it should be
easy to remember.
I'm far from done migrating stuff into the wiki, but I think there's already
quite a bit of useful information in there. I tried to prioritize
algorithms/data structures/techniques that are less known, and then listed
problems and articles that I thought were especially useful for
learning/practicing the given topic. In some cases I've additionally
extracted/written content about the given topic, with notes that po...
alt="AlgoWiki logo" />
124.
Northern Eurasia Finals 2020: Offline <img src="/predownloaded/c0/fe/c0fe3f2c5397274930f617ee822bdaecd5966927.jpg" align="right" style="height: 255px; margin: 10px;" alt="text"/>
Hello everyone!
After all online qualifiers, we are pleased to announce that the **Northern Eurasia Finals** and ICPC 2021 semi-final offline stage will take place this weekend on **April 3-4**!
<a href="https://youtu.be/65oO4Zauvgc" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(240, 170, 10);color: white;">ICPCLive broadcast</a>
<a href="http://nerc.itmo.ru/archive/2020/standings.html" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(76, 131, 195);color: white;">Standings</a>
<a href="https://codeforces.com/contests/1510" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(76, 131, 195);color: white;">Mirror</a>
<a href="http://nerc.itmo.ru/archive/2020/problems.pdf" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(76, 131, 195);color: white;">Problems</...
="height: 255px; margin: 10px;" alt="text"/>
125.
Unofficial Div 4 Round #2 Editorial This is the editorial for the [contest:102873].
We hope everyone had fun and enjoyed the contest!
[Video Editorial](https://youtu.be/FRWYFwSoiZw) by [user:demoralizer,2020-11-26]
Problem A — Catching the Impostor.
<spoiler summary="Tutorial">
Solution using frequency array:
Initialize an array of length $n$ with all the elements 0. This will be our frequency array. For every element we have in our list, we increase its frequency by one in the frequency array, $freq[arr[i]]+=1$. After we do this, we iterate through the frequency array and see how many elements have a frequency higher than 0 (it means they were mentioned in the list), let this number be $cnt$. Now if $cnt = n-1$ them we know for sure that who is the impostor, because all the other people are mentioned in the list. If $cnt ≠ n-1$ then we can't for sure know who is the impostor, so the answer is no.
Solution using set:
We introduce all the elements of the list in a set. A property of a set is th...
alt
Tutorial of Unofficial Div 4 Round #2 by ssense SlavicG
126.
Educational Codeforces Round 87 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1354] [contest:1354] will start.
**Please notice the unusual time.**
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Roman [user:Roms,2020-05-15] Glazov, Adilbek [user:adedalic,2020-05-15] Dalabaev, Vladimir [...
alt="Codeforces and Harbour.Space"
src="https://codeforces.com/predownloaded/2d/74
Announcement of Educational Codeforces Round 87 (Rated for Div. 2)
127.
ICPC NERC Huawei Challenge — Cloud Scheduling Challenge <img src="/predownloaded/50/6e/506e22d11e9f49d4ad8882c6c1877b5989589e60.png" align="right" style="height: 290px; margin: 10px;" alt="text"/>
Hello everyone!
We are thrilled to invite you to the great event — **ICPC NERC Challenge powered by Huawei 12 — 20 December 2020**.
<center style="margin: 2em"> <a href="https://codeforces.com/contests/1460" style="font-size: 15.0px;padding: 8.0px 14.0px;background-color: rgb(226, 36, 14);color: white;">Join to Challenge</a></center>
This contest is based on some real problems from Huawei Cloud team. The task is simplified, but still very challenging. You need to find a schedule for a variety of realistic problem instances, where the goal will be minimizing two different cost functions. There is a non-trivial tradeoff, decision you have to make, on how to choose what is best for a particular case. You will be provided with examples that can help you to tackle the problem. A good solution may also require diving deeper into ...
="height: 130px; margin: 10px;" alt="text"/>, ="height: 260px; margin: 10px;" alt="text"/>](https://youtu.be/29_RwCFtHFw), ="height: 290px; margin: 10px;" alt="text"/>
Announcement of NERC Challenge 2020: Marathon
128.
About DYNAMIC TECHNOLOGY LAB, Pte Ltd. <img src="/predownloaded/d0/25/d025e190ddafe382106a5faf70b723d41bd25dbf.png" align="right" style="height: 100px;" alt="DYNAMIC TECHNOLOGY LAB, PTE LTD LOGO"/>
### Hi Codeforces!
**We are [Dynamic Technology Lab, Pte Ltd. (DTL)](https://www.dytechlab.com)**, a _quantitative hedge fund_ engaging in global securities trading with multiple asset classes. Since our founding in 2009, from humble beginnings in a home garage, we are now a _sizable well-established financial institution_ with offices in **Singapore, Shanghai, Beijing, and Hanoi**. Our success is fueled by some of the most curious minds who are relentless in their _pursuit of innovation_.
As a **tech-focused Licensed Fund Management Company** under the Monetary Authority of Singapore, DTL is dedicated to producing _strong consistent returns_ for its investors by relying on mathematical and statistical models to drive its investment process.
## What is Quantitative Trading
<img src="/predownloaded/a8/89/a8891eb7ea5...
alt
129.
[Tuωutoωoial] Convex Polygon Counting Hi everyone, today I'm back with another blog that sadly, [user:nor,2023-10-19] won't have to spend 45 minutes GPT-ing my anime and kaomoji propaganda to read it. ૮₍ ˃ ⤙ ˂ ₎ა 👅
---
Not sure whether there is another blog explaining this technique in a "so many visualizations" manner.
There are so many paper about these problems in particular. So please put your opinions and any other similar techniques you know in the comment section 📃📃📜. I think this is a "very known technique" for <span class="rated-user user-red">GM</span>s, so you guys might want to skip reading this blog.
I also do expect this is a "very common geometry problem" in China or something but, here is my attempt on explaining it.
Here is a cute quote by me oωo
> When it comes to polygon problems, sometimes you have to see 🐦 🎀 𝓈𝑒𝑔𝓂𝑒𝓃𝓉 🎀 🐦 in...
alt="image
130.
Lattice paths and Lindström–Gessel–Viennot lemma In August 2022, I had a talk concerning lattice paths at a summer programming school in Khust, Ukraine. After, I realised that some aspects of my talk aren't well-known in the CP community and, in this blogpost, I'd like to very briefly and untidily (so feel free to ask for additional explanations by comments) share the main points of that talk.
I hope that ideas presented in the blog will help you sometime.
**1. Lattice paths**
**1.1. Walks without restrictions.**
**1.1.1.** We start from a rudimentary example. Consider a $N\times M$ grid and a robot (or a chip, or a ship, or anything else you wish) at $(0,0)$ (not a cell, an intersection point) which can move in the east unit direction and in the north unit direction. A route that the robot is able to make is said to be northeastern. How many northeastern paths are there? In fact, We can bijectively code any path with a corresponding string of the form $\uparrow\rightarrow\rightarrow\rightarrow\uparrow\rightarrow\dots$ o...
alt="drawing
131.
[Tutorial] Recurrent Sequences — Application of combinatorics in DP (basics) Hello Codeforces community! I decided to write tutorial about recurrent sequences, tutorial is about very basics of that topic. If you have little combinatorics knowledge, you will understand this tutorial easily. This is my first tutorial, so this can be easy for you and there can be mistakes. Probably all Div1 users knows all things in this tutorial :) Hope this tutorial will help you. If you have any questions/suggestions please write in comments.
**Recurrent Sequences — Application of combinatorics in DP**
Let’s start with a problem to this topic.
**Problem.** In how many different ways you can write 8 (+) and 5 (-) signs consecutively such that no two (-) signs are adjacent are adjacent.
Solution of problem is easy. Let’s write (+) signs after 9 `m`s:
`m + m + m + m + m + m + m + m + m`
Now let's change 5 of `m`s to (-) sign. Actually, problem has been solved, no 2 (-) signs are consecutive. So, answer is $\binom{9}{5}$ (because there are 9 `m`s and we h...
alt="tutorial" border="0">, alt="tutorial1" border="0">
132.
VK Cup 2018 — анонс и регистрация Привет, Codeforces!
Мы с радостью сообщаем вам, что компания [ВКонтакте](http://vk.com/) совместно с площадкой Codeforces вновь проводит чемпионат VK Cup. К участию в VK Cup 2018 допускаются команды до двух человек, так как практика <i>парного программирования</i> широко распространена во всем мире, в том числе и ВКонтакте. За призы и звание победителя приглашается побороться русскоязычным молодым специалистам, студентам, школьникам и просто любителям алгоритмов и программирования.
Лучшие 20 команд по результатам отборочных интернет-этапов будут приглашены в финал соревнования, который состоится 10 — 13 августа 2018-го года в прекрасном городе Санкт-Петербурге. Компания ВКонтакте покроет расходы на проезд и проживание финалистов, которые будут бороться не только за звание лучших из лучших, но и призовой фонд чемпионата. Как и в прошлом году призы соревнования связаны с круглыми числами в двоичной системе счисления:
- **1 место — 1048576 рублей**
- 2 местo — 524288 рубле...
> alt <https://vk.com/vkcup>
133.
Codeforces Global Round 17 Editorial ###[problem:1610A]
Idea: [user:Anti-Light,2021-11-24], Preparation: [user:DeadlyCritic,2021-11-24]
<spoiler summary="Hints">
<spoiler summary="Hint 1">
$ans \le 2$
</spoiler>
<spoiler summary="Hint 2">
If $n = 1$ and $m = 1$ then $ans = 0$. <a href="https://emoji.gg/emoji/5500-thosewhoknow"><img src="https://emoji.gg/assets/emoji/5500-thosewhoknow.png" width="20px" height="20px" alt="ThoseWhoKnow"></a>
</spoiler>
</spoiler>
<spoiler summary="Solution">
[tutorial:1610A]
</spoiler>
<spoiler summary="Implementation">
~~~~~
#include <bits/stdc++.h>
using namespace std;
int main()
{
ios::sync_with_stdio(false);
cin.tie();
cout.tie();
int t;
cin >> t;
while(t--){
int n, m;
cin >> n >> m;
if(n == 1 && m == 1){
cout << "0\n";
}
else if(min(n, m) == 1){
cout << "1\n";
}
else cout << "2\n";
}
}
~~~~~
</spoiler>
###[p...
" height="20px" alt="ThoseWhoKnow">
Tutorial of Codeforces Global Round 17
134.
Microsoft Q# Coding Contest – Summer 2020 — Warmup: editorial The warmup round is over; I hope you enjoyed it and learned something new in the process!
Here are the explanations for the contest problems and pointers some extra resources that can help you learn more about the respective topics before the main contest. You should also be able to see the solutions of the contest participants and to solve the problems in practice mode.
## A: "Distinguishing Unitaries" problems
Here is the editorial for the problems: https://assets.codeforces.com/rounds/1356/A1-A5.pdf.
> These problems are [published in the Quantum Katas](https://github.com/microsoft/QuantumKatas/tree/master/DistinguishUnitaries), so that you can see the testing harness used for the problems and use it for testing your solutions in the main contest.
## B: Reversible computing
Reversible computing is a branch of quantum computing that deals with expressing classical computations in a reversible manner (i.e., so that the computation has a unique input state for each ou...
alt="D1 training data" width="45%"/>
135.
ICPC 2023 Online Spring Challenge powered by Huawei <img src="/predownloaded/af/22/af228fee1abb015217d8c524de74898aeff36419.png" align="right" style="height: 280px;" alt="text"/>
Hello, Codeforces!
**UPD:** Challenge is over. You can find results [in this post](https://codeforces.com/blog/entry/115695)
We are happy to invite you to an exciting online event: ICPC 2023 Online Spring Challenge powered by Huawei, which will start on [April 13, 2023, 11:00 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICPC+2023+Online+Spring+Challenge+powered+by+Huawei&iso=20230413T11&p1=1440).
In this Challenge, you will have a unique chance:
- to compete during 14 days online challenge
- to solve 1 exciting problem prepared by Huawei
- to win amazing prizes from Huawei!
As a special prize, Huawei together with ICPC Foundation will provide the travel trip to the 46th Annual ICPC World Finals in a guest role!
Everyone is welcome to participate. It is an individual competition.
**ICPC 2023 Online Spring Challenge p...
="height: 280px;" alt="text"/>
Announcement of ICPC 2023 Online Spring Challenge powered by Huawei
136.
TypeDB Forces 2023 (Div. 1 + Div. 2, Rated, Prizes!) Greetings, CodeForces!
[user:jiangtaizhe001,2023-01-27], [user:qzhwlzy,2023-01-27] and I [user:rsj,2023-01-27] are more than excited to invite you to participate in [contest:1787], which starts on [contest_time:1787].
The round is open and rated for everyone. You are given **9** problems, no subtasks or interactive problems, and you have **3** hours to solve them. It is recommended to read all problems. The statements were made as briefly and clearly as we could. Enjoy the contest!
**UPD:** Score distribution: $500-1000-1750-2000-2250-2500-3250-3500-3750$
Sincere thanks to:
- [user:74TrAkToR,2023-01-27], for a long-term, tough and perfect coordination.
- [user:qzhwlzy,2023-01-27], for writing and polishing statements and tutorials, and sparky ideas.
- [user:jiangtaizhe001,2023-01-27], for helping me a lot in preparation.
- [user:275307894a,2023-01-27] and [user:A_zjzj,2023-01-27], for providing wonderful problems and solutions.
- [user:carnation13,2023-01-27], [user:...
alt="TypeDB" src="https://codeforces.com/predownloaded/5b/53
Announcement of TypeDB Forces 2023 (Div. 1 + Div. 2, Rated, Prizes!)
137.
Codeforces Round #777 Editorial Задача A. Идея [user:FairyWinx,2022-03-11]
<spoiler summary="Подсказка 1">
В оптимальном ответе максимальное количество цифр, так что нужно использовать только цифры $1,2$.
</spoiler>
<spoiler summary="Подсказка 2">
Чередуйте эти цифры, чтобы не было соседних одиннаковых цифр.
</spoiler>
<spoiler summary="Решение">
Так как мы хотим максимизировать нужное нам число, найдем сначало самое длинное подходящее число. Очевидно, что для этого лучше использовать только цифры $1$ и $2$. Поэтому ответ всегда имеет вид $2121\ldots$ или $1212\ldots$. Первый вариант оптимален, когда $n$ имеет остаток $2$ или $0$ по модулю $3$, в противном случае оптимален второй вариант.
Ниже приведен пример аккуратной реализации.
</spoiler>
<spoiler summary="Реализация">
~~~~~
#include <bits/stdc++.h>
using namespace std;
void solve() {
int n;
cin >> n;
int type;
if (n % 3 == 1)
type = 1;
else
type = 2;
int sum = 0;
while (sum != ...
" alt="dw_smiley"> , .gif" alt="dw_smiley">
Tutorial of Codeforces Round 777 (Div. 2)
138.
A Step-by-step Guide to Configure Topcoder Competitive Environment <h3><b>Step 1: Get a Topcoder account if you don't already have one.</b></h3>
Address: http://www.topcoder.com/talent/
<img alt=" " src="/predownloaded/3d/4b/3d4b2c0adc4d14af81a96fd61ca41e5836a5e1fb.png" style="max-width: 100.0%;max-height: 100.0%;" /></p>
Click on the "JOIN TOPCODER" button, and fill in the form to register.
<img alt=" " src="/predownloaded/00/7f/007f49a53c95b30b66ba6bdd76453256665b35cb.png
" style="max-width: 100.0%;max-height: 100.0%;" /></p>
<h3><b>Step 2: Download and install Java Runtime Environment.</b></h3>
Address: https://www.java.com/en/download/manual.jsp
<h3><b>Step 3: Download the topcoder applet.</b></h3>
Address: https://www.topcoder.com/contest/arena/ContestAppletProd.jnlp
I strongly recommend you to put the above jnlp into the same folder of executable file "javaws" (Java Web Start Luncher).
<img alt=" " src="/predownloaded/65/c4/65c4d4e5471e3ca6f9ca812f946f885cf2a35815.png" style="max-width: 100.0%;max-height: 100.0%;" ...
alt=" " src="/predownloaded/00/7f/007f49a53c95b30b66ba6bdd76453256665b35cb.png
" style="max, alt=" " src="/predownloaded/07/87/07876393cc59d618efde16cab4b879688d2491cf.png"
style="max, alt=" " src="/predownloaded/1e/59/1e5927a64d29c0ebc64dacb51df9a7caf9c25dde.png"
style="max, alt=" " src="/predownloaded/3d/4b/3d4b2c0adc4d14af81a96fd61ca41e5836a5e1fb.png"
style="max, alt=" " src="/predownloaded/43/69/4369e703939617beec15977181674420d1726718.png"
style="max, alt=" " src="/predownloaded/4b/e2/4be20cb07c20c49042e514386373610caa614f32.png"
style="max, alt=" " src="/predownloaded/54/3d/543d9979290f6ce3232eb742819e96144a2d6112.png"
style="max, alt=" " src="/predownloaded/65/c4/65c4d4e5471e3ca6f9ca812f946f885cf2a35815.png"
style="max, alt=" " src="/predownloaded/84/a5/84a535ed3853f1a0d01ae95956630d3dab49aaef.png"
style="max, alt=" " src="/predownloaded/9b/9d/9b9d60092c7c9650fd214aace6cc2637de719537.png"
style="max, alt=" " src="/predownloaded/a2/af/a2af535fe9522b5cbd350c477f9f93a9aa6a6cc4.png"
style="max, alt=" " src="/predownloaded/a9/7a/a97af3249bb410acdb22d68efe7210fb5c937279.png"
style="max, alt=" " src="/predownloaded/bf/93/bf939ba4f03be9854c05219a5520050d002d45fb.png"
style="max, alt=" " src="/predownloaded/cb/94/cb946846da6fecef64047308d4b94fcc4db2d45b.png"
style="max, alt=" " src="/predownloaded/e9/ef/e9ef1adc5c329e107b07da73062971e95cb10617.png"
style="max, alt=" " src="https://images.ctfassets.net/piwi0eufbb2g/78KiAR7o4p2VJQmZfxPvTj
139.
Operating Systems Notes If you are struggling with the right track and a 10-min read for Operating systems from beginning to end, you're at the right place. Even I am not sure where to start, but we would figure it and if you are reading this, I have successfully completed these notes or at least am on right track.
Let's start our struggle for OS:
### The Track
I found many resources to learn, let's just list all:
(Galvin Concise PPTs)[https://www.os-book.com/OS9/slide-dir/index.html]: These were great but I felt that these are a little bit too much, so here are the chapters we would do:
1. Processes
2. Threads
3. Process Synchronization
4. CPU Scheduling Algorithms
5. Deadlocks
6. Main memory
7. Virtual memory
8. Virtual Machines
> I am skipping the introduction of OS for now as it was not that important, this is going to be a fast article that works like a last night dose.
<spoiler summary="A simple introduction(May skip if you are already familiar)">
An Operating system is like a...
140.
ICPC 2022 Online Challenge powered by HUAWEI <img src="/predownloaded/af/22/af228fee1abb015217d8c524de74898aeff36419.png" align="right" style="height: 300px;" alt="text"/>
Hello, Codeforces!
We are happy to invite you to an exciting online event: **ICPC 2022 Online Challenge powered by HUAWEI**，which will start on **[September 15, 2022, 00:00 UTC (UTC+0)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=ICPC+2022+Online+Challenge+powered+by+HUAWEI&iso=20220915T00).**
In this Challenge, you will have a unique chance:
- to compete for **2 weeks online** during the challenge
- to solve **1 or 2 problems** prepared by different business domains of HUAWEI
- to win amazing prizes from HUAWEI!
As a special prize, HUAWEI together with ICPC Foundation will provide the travel trip to the 46th Annual ICPC World Finals in a guest role to the 2 winners (1 winner for each problem)!
**Everyone is welcome to participate. It is an individual competition.**
**ICPC 2022 Online Challenge powered by HUAWEI** (open to t...
="height: 150px;margin: 10px 20px 20px;" alt="text"/>, ="height: 300px;" alt="text"/>
Announcement of ICPC 2022 Online Challenge powered by HUAWEI - Problem 1
Announcement of ICPC 2022 Online Challenge powered by HUAWEI - Problem 2
141.
There is a rating inflation abuser who controls hundreds of alts. What the hell is going on?
Someone is making intended rating inflation with hundreds of alts.
Please ban those accounts, and make some policy to save rating atmosphere from abusers.
So far, I found at least 200 dummy accounts in today round's registrants list.
142.
VK Cup 2015 — анонс и регистрация Добрый день, Codeforces!
Мы рады сообщить вам, что в этом году компания [ВКонтакте](http://vk.com/) совместно с площадкой Codeforces проведет обновленный VK Cup. Во многих IT-компаниях, в том числе и ВКонтакте, широко применяется практика <i>парного программирования</i>. VK Cup 2015 предлагает участникам попробовать именно такой формат, допуская к участию команды до двух человек. За призы и звание победителя приглашается побороться русскоязычным молодым специалистам, студентам, школьникам и просто любителям алгоритмов и программирования.
Лучшие 20 команд по результатам отборочных интернет-этапов будут приглашены в финал соревнования, который состоится в июле 2015-го года в Санкт-Петербурге. Компания ВКонтакте покроет расходы на проезд и проживание финалистов, которые будут бороться не только за звание лучших из лучших, но и призовой фонд чемпионата. В этом году мы сделали призы соревнования круглыми числами в двоичной системе счисления:
* **1 место — 1048576 рублей**...
> alt <https://vk.com/vkcup>
143.
Teamscode Spring 2023 Editorial This is the editorial for a recent contest [Teamscode](https://www.teamscode.org/). The problems are open for upsolving on [this gym](https://codeforces.com/gym/104287). Problems were prepared by [user:oursaco,2023-04-06], [user:dutin,2023-04-06], [user:thehunterjames,2023-04-06], [user:Bossologist,2023-04-06], [user:Esomer,2023-04-06], and me.
### [A. What do you do when the contest starts? Are you busy? Will you solve Bingo?](https://codeforces.com/gym/104287/problem/A)
<spoiler summary = "Editorial">
<spoiler summary = "Are you busy?">
1. WorldEnd/SukaSuka
2. Bocchi the Rock
</spoiler>
<spoiler summary = "No Sweep">
1. Thomas
</spoiler>
<spoiler summary = "Multiplication Table">
1. Lycoris Recoil
</spoiler>
<spoiler summary = "Greatest Common Multiple">
1. Bokuben
</spoiler>
<spoiler summary = "A Certain Scientific Tree Problem">
1. A Certain Scientific Railgun
</spoiler>
<spoiler summary = "Two and Three">
1. Quintessential Quintluplets...
int ind = N - i - 1; alt = a[ind];
Tutorial of Teamscode Spring 2023 Contest
144.
Hack me! — Good Bye 2014! Still in buoyant humour after [contest:500]? While waiting for the editorial, maybe you would like to know why there were so many hacks in the last round of this year?
As always, please share you thoughts, ideas or maybe hacks :)
Previous posts can be found [here](http://codeforces.com/search?query=hackme).
[cut]
<h3>Stats</h3>
Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other* | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>|<small>Hackers efficiency**</small>|
:---:|:---:|:---:|:---:|:---:|:---:|:---:|
<small> [problem:500A] </small> | 199 (40.61%) | 124 (25.31%)| 167 (34.08%) | 490 | 375 (9.32%) | 3650 (90.68%) | 4025 | 34.67%
<small> [problem:500B] </small> | 738 (67.40%) | 214 (19.54%)| 143 (13.06%) | 1095 | 573 (24.89%) | 1729 (75.11%) | 2302 | 56.29%
<small> [problem:500C] </small> | 0 (0.00%) | 9 (75.00%)| 3 (25.00%) | 12 | 23 (1.08%) |...
alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500A.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500B.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500C.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500D.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500E.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500F.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500G.png, alt="Here should be graph." src="http://www.test.weaselcrow.com/cfhacks/500L.png
145.
Invitation to TOKI Regular Open Contest #28 (Div. 2 Only, based on BNPC-HS 2022 Elimination Round) <p><img src="https://media.discordapp.net/attachments/976314385721077762/1032912348178030642/header.png" alt="" width="700" /></p>
We are excited to invite you to [TOKI Regular Open Contest #28 (Div. 2 Only, based on BNPC-HS 2022 Elimination Round)](https://tlx.toki.id/contests/troc-28-div-2) on [Sunday, October 23rd 2022 19:05 UTC+7](https://www.timeanddate.com/worldclock/fixedtime.html?msg=TOKI+Regular+Open+Contest+%2328+%28Div.+2+Only%2C+based+on+BNPC-HS+2022+Elimination+Round%29&iso=20221023T1905&p1=3909)
Your rating should **be less than 2000 or not yet rated** in TLX to participate in this contest.
The contest will be **2 hours long** and will feature **6 problems**. Note that you should participate in the contest **individually**.
The problems were written by [user:vioalbert,2022-10-21], [user:rfpermen,2022-10-21], [user:Tyroflex,2022-10-21], [user:Trainerherp,2022-10-21], [user:Kresna,2022-10-21], [user:ConvexHull89,2022-10-21], [user:felix_suharjo,2022-10-21].
P...
/header.png" alt="" width="700" />
146.
Hack me! (CF Round #263, Div. 2) Welcome again!
I decided to split statistics for both division. Post for first division <strike>will be added later</strike> is <a href="http://codeforces.com/blog/entry/13572">here</a>.
So, let's look at hacks in [contest:462].
<small><strike>Some statistics are missing — I have some problems with downloading all data (Codeforces seems little crowded today). They will be also added later.</strike></small>
**Update**: Europe went asleep, so I added missing stats.
[cut]
<h3>Stats</h3>
Problem | Successful hacks | Unsuccessful hacks | Other | Sum |
:---:|:---:|:---:|:---:|:---:|
[problem:462A] | 5 (17%) | 25 (83%) | 0 (0%) | 30 |
[problem:462B] | 1193 (71%) | 188 (11%) | 306 (18%) | 1687 |
[problem:462C] | 0 (0%) | 55 (36%) | 98 (64%) | 153 |
### Fastest hackers
Problem | Time | Hacker | Defender | Hack
:---:|:---:|:---:|:---:|:---:|
[problem:462A] | 00:50:08 | [user:ak.bewildered,2014-08-26] | [user:abdohammam95,2014-08-26] | <a href="http://codefo...
alt="Here should be graph." src="http://www.weaselcrow.com/cfhacks/462b.png"
width
147.
Longest subsequence which is a union of K increasing subsequences I was reading [user:mango_lassi,2022-03-24]'s [blog](https://codeforces.com/blog/entry/98167) and in one of the [paper](https://www.sciencedirect.com/science/article/pii/0001870874900310) referred in his blog, I found a $O(N^2)$ algorithm for constructing a longest k-increasing subsequence (a subsequence of maximum length which is a union of k increasing subsequences). While implementing it, [user:koosaga,2022-03-24] told me about the problem E in "AMPPZ-2015 MIPT-2015 ACM-ICPC Workshop Round 1" (id #6275 in opentrain) where the problem asks to construct such subsequence with constraint $N \le 2 \cdot 10^5$ and $K \le 20$.
The official solution runs in $O(N \cdot K \cdot (K + \log(N)))$. The first half seems to be doing the RSK mapping, but I couldn't figure out why the second half works. It seems to be unrolling the mapping from the back, and maintaining $K$ intervals for each row in the tableau. And the editorial only explains the first half. Can someone please explain why it work...
alt <https://ibb.co/qdjMBpk>
148.
VK Cup 2016 — анонс и регистрация Привет, Codeforces!
Мы с радостью сообщаем вам, что компания [ВКонтакте](http://vk.com/) совместно с площадкой Codeforces вновь проводит чемпионат VK Cup. К участию в VK Cup 2016 допускаются команды до двух человек, так как практика <i>парного программирования</i> широко распространена во всем мире, в том числе и ВКонтакте. За призы и звание победителя приглашается побороться русскоязычным молодым специалистам, студентам, школьникам и просто любителям алгоритмов и программирования.
Лучшие 20 команд по результатам отборочных интернет-этапов будут приглашены в финал соревнования, который состоится в июле 2016-го года в прекрасном городе Санкт-Петербурге. Компания ВКонтакте покроет расходы на проезд и проживание финалистов, которые будут бороться не только за звание лучших из лучших, но и призовой фонд чемпионата. Как и в прошлом году призы соревнования связаны с круглыми числами в двоичной системе счисления:
- **1 место — 1048576 рублей**
- 2 местo — 524288 рублей
- 3 местo — ...
> alt <https://vk.com/vkcup>
149.
Educational Codeforces Round 149 [Rated for Div. 2] Hello Codeforces!
On [contest_time:1837] [contest:1837] will start.
Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://mirror.codeforces.com/blog/entry/51208">blog post</a>.
This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.
You will be given **6 or 7 problems** and **2 hours** to solve them.
The problems were invented and prepared by Adilbek [user:adedalic,2023-05-24] Dalabaev, Ivan [user:BledDest,2023-05-24] Androsov, Maksim [user:Neon,2023-05-24] Mesche...
alt="Harbour.Space" src="https://codeforces.com/predownloaded/56/04
Announcement of Educational Codeforces Round 149 (Rated for Div. 2)
Codeforces (c) Copyright 2010-2024 Mike Mirzayanov
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