You can use several words in query to find by all of them at the same time. In addition, if you are lucky search understands word forms and some synonyms. It supports search by title and author. Examples:

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  • "vk cup" — use quotes to find phrase as is
  • title:educational — search in title

Results

 
 
 
 
1.
By Sooke, 16 months ago, In English
Codeforces Round #635 _Riichi...Tsumo! 2 han 2000 points!_ ![ ](/predownloaded/a9/4f/a94f898a1c9c906cd81ecd483c3ec9ff5e6315c0.png) Hi! Have you ever heard of the game called _Mahjong Soul_? It is a Japanese Mahjong game that is famous for the adorable characters. We are excited to invite you to take part in [Codeforces Round #635](https://codeforces.com/contests/1336,1337), where you can help the characters in trouble. This round will be held on [contest_time:1336]. Most importantly, it is **rated** for both divisions! Each division will be given **6 problems** and you will have **2.5 hours** to solve them. An interactive problem may be found in this round. If you are not familiar with interactive problems, you can learn about them [here](https://codeforces.com/blog/entry/45307). The problems were prepared by [user:EternalAlexander,2020-04-14], [user:ustze,2020-04-14] and me [user:Sooke,2020-04-14]. We sincerely thank [user:isaf27,2020-04-14] for reviewing and coordinating the round, and ...
Codeforces Round #635, /a94f898a1c9c906cd81ecd483c3ec9ff5e6315c0.png) Hi! Have you ever heard of the game called _Mahjong Soul_? It is a Japanese Mahjong

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2.
By parveen1981, history, 2 months ago, In English
I compiled a list of almost all useful blogs ever published on Codeforces [update: till 09.06.2021] <h3 style="color:red">If there are any blogs that I have missed, please tell in the comment section. Thank you.</h3> # Mathematics Stuff - [Number Theory in Competitive Programming [Tutorial]](https://codeforces.com/blog/entry/46620) - [Number of points on Convex hull with lattice points](https://codeforces.com/blog/entry/62183) - [FFT, big modulos, precision errors.](https://codeforces.com/blog/entry/48465) - [Number of ways between two vertices](https://codeforces.com/blog/entry/19078) - [Mathematics For Competitive Programming](https://codeforces.com/blog/entry/76938) - [FFT and NTT](https://codeforces.com/blog/entry/19862) - [Burnside Lemma](https://codeforces.com/blog/entry/51272) - [Number of positive integral solutions of equation 1/x+1/y=1/n!](https://codeforces.com/blog/entry/76836) - [On burnside (again)](https://codeforces.com/blog/entry/64860) - [Simple but often unknown theorems/lemmas/formula? Do you know?](https://codeforces.com/blog/entry/55912) - [Probabili...
I compiled a list of almost all useful blogs ever published on Codeforces [update: till 09.06.2021], /entry/68616) - [Improving my Thinking Ability](https://codeforces.com/blog/entry/77493) - [AGood, ://codeforces.com/blog/entry/77616) - [A Well-known Data Structure -- Version Tree](https://codeforces.com

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3.
By McDic, history, 16 months ago, In English
Codeforces Round #633 **내가 돌아왔다!** (Hello, Codeforces!) I am thrilled to introduce you to [Codeforces Round #633](https://codeforces.com/contests/1338,1339). Followings are basic information: - This contest will take place on [contest_time:1338]. - The round is **rated for all participants** who can understand this announcement. There will be two divisions. - There are **5 problems** in each division and you will have **2 hours** to solve it. - Score distribution will be announced later. Followings are contributors: - **Authors**: [user:McDic,2020-04-10] (All Div.2 problems and Div.1 D), [user:tzuyu_chou,2020-04-10] (Div.1 E) - **Coordinator**: [user:antontrygubO_o,2020-04-10] - **Testers**: - **Phase 1** (When this round was supposed to be Div.2): [user:dorijanlendvaj,2020-04-10], [user:SoulTch,2020-04-10], [user:pajenegod,2020-04-10], [user:AryaPawn,2020-04-10], [user:Rahul,2020-04-10], [user:mcdx9524,2020-04-10], [user:300iq,2020-04-10], [user:Nemo,2020-04-10], [user:tfg,2020-04-10]...
Codeforces Round #633, **내가 돌아왔다!** (Hello, Codeforces!) I am thrilled to introduce you to [Codeforces Round #633, - [user:antontrygubO_o,2020-04-10] is the most intense coordinator I have ever met. He rejected

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4.
By AquaMoon, history, 4 weeks ago, In English
Codeforces Round #732 Hello, Codeforces! I'm glad to invite you to [contest:1545] and [contest:1546], which will be held on [contest_time:1545]. **Note the unusual start time of the round.** The round will be rated for both divisions. Each division will have **6 problems** and **2.5 hours** to solve them. There may or may not be an interactive problem, so I suggest you should read the [guide for interactive problems](https://codeforces.com/blog/entry/45307). All problems were written and prepared by [user:CoupDeGrace,2021-07-02], [user:kuangbin,2021-07-02], [user:mejiamejia,2021-07-02], [user:Heltion,2021-07-02], [user:Melacau,2021-07-02], [user:Nanako,2021-07-02], [user:GOATWU,2021-07-02], [user:Cirno_9baka,2021-07-02], [user:Suiseiseki,2021-07-02], [user:ODT,2021-07-02], [user:box,2021-07-03], [user:Ynoi,2021-07-02], [user:syh0313,2021-07-02], [user:wh0816,2021-07-02] and me. And thanks to [user:QAQAutoMaton,2021-07-02], [user:gamegame,2021-07-02], [user:starusc,2021-07-02], [user:interesting...
Codeforces Round #732, -07-04] for testing and good advice, [user:isaf27,2021-07-06] for his excellent round coordination

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5.
By AmShZ, history, 2 months ago, In English
Codeforces Round #722 Hi Codeforces! [user:Dio,2021-05-22], [user:Keshi,2021-05-22], [user:Tet,2021-05-22], [user:alireza_kaviani,2021-05-22], [user:-Zeus-,2021-05-22], [user:alishahali1382,2021-05-22] and I are delighted to invite you to participate in [contest:1528] and [contest:1529], which will be held at [contest_time:1528]. Each division will have **6 problems** and **2 hours and 15 minutes** to solve them. The curse has finally been lifted! We are proud to announce that [user:antontrygubO_o,2021-05-22] didn't reject even a single task from the Div. 1 part! Huge thanks to the following people: - [user:antontrygubO_o,2021-05-22] for being an outstanding coordinator; This round wouldn't have happened if it weren't for him. - Our ever-growing army of testers [user:gamegame,2021-05-22], [user:Amoo_Safar,2021-05-22], [user:Atreus,2021-05-22], [user:dorijanlendvaj,2021-05-22], [user:aarr,2021-05-22], [user:1-gon,2021-05-22], [user:EnEm,2021-05-22], [user:N.N_2004,2021-05-22], [user:AaParsa,20...
Codeforces Round #722, : - [user:antontrygubO_o,2021-05-22] for being an outstanding coordinator; This round wouldn't have

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6.
By MikeMirzayanov, 3 years ago, translation, In English
Hello, ITMO! <img src="https://assets.codeforces.com/images/itmo-logo.png" style="margin:1em 1em 1em 1em; float:right;"/> Hi Codeforces! For you, perhaps it was yet another Codeforces round. But not for me. [contest:1066] is the first round tested on new judging servers at ITMO University. And this is not just an update of location. Ta-dam! Now your solutions will be judged on the new Intel i3-8100 processors. And this is not all news. The number of judging servers has increased, which means fewer queues during rounds! I am pleased to announce that now I live in St. Petersburg, I work at ITMO, and Codeforces is gradually moving from the walls of dear to me Saratov University to ITMO University. The decision to move was not easy for me. My plan is that, based on ITMO, I can focus more on Codeforces development and work on the platform. The number of world champions per square meter is simply overwhelming, and working with a large team of such enthusiasts (and professionals!) of sports pro...
. A good Internet connection between SSU and ITMO is encouraging. All the planned work will adapt, ; float:right;"/> Hi Codeforces! For you, perhaps it was yet another Codeforces round. But not for me

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7.
By TeaPot, history, 4 years ago, In English
Will competitive programming ever become a real sport? I always was dreaming that one day competitive programming will become a real sport, not just activity for a small group of participants. Why? Because I don't really like working and my tries to do some science were totally unsuccessful. It would be cool to live just by doing what you like. Very childish, I know. But this blog is not about if competitive programming is important or are there any ways to make it interesting to watch to wider audience. I am just trying to understand, is it currently moving toward real sport or away from it? And I get some mixed signals about that: Bad signals: - Big onsites (like GCJ or TCO) seem to cut the number of participants and the amount of prizes. - Some onsite-finals are turning to online-finals. For example, several years ago we had Russian Code Cup onsite in Russia, currently RCC Finals is online. - Some big companies are turning away from sport programming (IBM is stopping sponsorship of ACM ICPC). Good signals: - Some ne...
Will competitive programming ever become a real sport?, away from sport programming (IBM is stopping sponsorship of ACM ICPC). Good signals: - Some

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8.
By MikeMirzayanov, 18 months ago, translation, In English
Codeforces: Results of 2019 <a style="float:right; display: inline-block; margin:0 1em 1em 2em; max-width: 60%;" href="https://codeforces.com/10years"/> <img style="max-width:100%" src="https://assets.codeforces.com/images/codeforces-10-years-300.png"/> </a> Hi Codeforces! The platform recently turned 10 years old. We accept your congratulations at <a href="https://codeforces.com/10years">https://codeforces.com/10years</a>. Please review the progress in 2019 and support the anniversary crowdfunding campaign. Your donation will be a contribution to the future of Codeforces, will help its development and work. We need resources to continue to host rounds, not to stop developing, to innovate and to maintain the existing infrastructure. In 2019, together with numerous writers the coordinators worked on problems: [user:KAN,2020-02-06], [user:300iq,2020-02-06], [user:cdkrot,2020-02-06], [user:arsijo,2020-02-06] and recently joined [user:isaf27,2020-02-06]. And this year, rounds coordinated by other exper...
had more rounds than ever before! Time to take stock of 2019. #### Partner Events We

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9.
By Ari, history, 2 months ago, In English
On Problems vs. Questions in Competitive Programming: My solution _TL;DR: The most reasonable solution to the problems vs. questions debate is to use none of the currently accepted terms._ As we have seen many times, particularly over the past few days, the task of assigning a label to the activities we perform as competitive programmers is a bigger problem than one might think at first. Time and time again we have seen people questioning what we should call our activities, often to the point of eliciting some rather harsh responses. To give some context to this discussion, I will focus on two of the terms that members of the community have adopted over the years, _problems_ and _questions_. (Sorry task lovers! You have some fine points for sure, we frequently talk about subtasks rather than subproblems or subquestions after all :P). All quotations here are posted anonymously, but if you want to claim ownership of one of them or have one removed, just tell me. If you are familiar with the arguments, feel free to skip to the final section of the...
? Well, the use of terms such as questions instead of problems, or other terms such as giving

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10.
By kostka, 6 years ago, In English
Good Bye 2015! (review, pt. 1) Hey there, I couldn't sleep, so I spend almost an hour to play with some Python and answering some questions about "who was... in 2015 on Codeforces" (also checking if I still remember anything :)). So &mdash; have you ever wondered who was the best in this year on Codeforces? I will try to answer to your (and mostly mine) questions. Here is the first part (and maybe the last :)) of this year review. [cut] In this year, there were 105 contests on Codeforces, 12 of them were not on CF rules, so there were removed from the rest of review (i,e, Educational Rounds, some ACM contests and so on). ### Most problems solved | Handle | Contests | Sum of tasks solved | Average | | :---: | :---: | :---: | :--- : | | [user:xauoyero,2015-12-31] | 52 | 112 | 2.153846 | | [user:alex_bucevschi,2015-12-31] | 53 | 106 | 2.000000 | | [user:Shavkat_Aminov,2015-12-31] | 54 | 105 | 1.944444 | | [user:ershov.stanislav,2015-12-31] | 31 | 100 | 3.225806 | | [user:Endagorion,2015-12-31] |...
Good Bye 2015! (review, pt. 1), :)). So — have you ever wondered who was the best in this year on Codeforces? I will try to answer

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11.
By cip999, 9 days ago, In English
Editorial of Global Round 15 We hope you liked the problems! Before we go ahead with the editorial, let us make some general comments about this round. Problems A, B, C, D, E, F are "div 2" problems, while problems G, H, I are meant to be solved by Grandmasters. Overall, our goal was to provide a problemset that could be enjoyable for a wide range of participants and such that the winner could solve all the problems. There were three big "jumps" in the difficlty gaps between consecutive problems. Problems A and B are meant to be easy, many contestants have the skills and the techniques to attack them (and, maybe, to solve them). Problems C, D, E, F are gradually harder but the difficulty gap between C and F is not as large as usual (and this is reflected in the score distribution). The same holds for problem G, H, I; the difficulty gap between G and I is relatively small (but there is a big score difference because coding I is much harder). Sadly, we discovered 14 minutes into the round that problem I...
Editorial of Global Round 15, thoughts from cip999"> This was the first round ever that I (co-)organized, so I'm eager to share some

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12.
By Eddagdeg, history, 19 months ago, In English
30 day challenge Hello everyone ! I'm fourth year software engineering student.I've been doing CP for three years .I learned many algorithms and I solved many problems but the problem is that I cannot do my best during contests for that I'm going to set myself a 30 day challenge :making virtual participation every day in a contest and upsolve all unsolved problems. so if any one remember a good round (quality of problems,gap of difficulty between problems)please share it with me. I'll update the blog every day to post my rating in the contest and let's see if this challenge gonna make me a junior tourist ^__^. first contest:[round 422](https://codeforces.com/contest/822) [rank](https://codeforces.com/contest/822/standings/participant/31810110#p31810110):1368 second contest: [round 480](https://codeforces.com/contest/980) [rank](https://codeforces.com/contest/980/standings/participant/31837825#p31837825):1058 third contest: [round 353](https://codeforces.com/contest/675) rank:[1398...
every day in a contest and upsolve all unsolved problems. so if any one remember agood round, /contest/939/standings/participant/31935860#p31935860) (best rank I ever achieved ^___^)

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13.
By kpw29, 11 months ago, In English
Meet IT Codeforces Round Editorial Thank you very much for taking part in the contest! <spoiler summary="Contest timeline"> - -0:05. Starting the chat with the Questions Answering team: [user:tnowak,2020-11-15] and our beloved coordinator [user:antontrygubO_o,2020-11-15]. We hope that there won't be that many questions :) - -0:01. One minute to go! I hope that everything goes smoothly. I'm so afraid of posting the editorial accidentally that I moved this timeline into another blog... - 0:01. First blood in Div2! Congratulations to [user:majorro,2020-11-15]!. - 0:03. First blood in Div1 as well! Congratulations to [user:Errichto,2020-11-15], your knapsack is ready for a journey to win! - 0:04. [user:Sho10,2020-11-15] first to solve Div2B. Well done! - 0:05. We also have the first question. So far so good... - 0:06. [user:Um_nik,2020-11-15] gets the first pretests pass in Div1B. The cheaters are caught! - 0:09. [user:bandiaoz,2020-11-15] packs the first Knapsack in Div2! A difficulty spike is coming... - 0:12....
Meet IT Codeforces Round Editorial, ] first to solve Div2B. Well done! - 0:05. We also have the first question. So far sogood... - 0:06

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14.
By mohammedehab2002, 4 months ago, In English
Codeforces Round #716 (Div.2) Hi everyone! Codeforces round #716 will take place on [contest_time:1514]. It's rated for the second division, but, as usual, first division participants can take part out of competition. The problems are based on the Egyptian IOI qualification, and they were created by me and [user:mahmoudbadawy,2021-04-17]. I'd like to thank: - [user:KAN,2021-04-17] and [user:Nebuchadnezzar,2021-04-17] for their excellent coordination. - [user:antontrygubO_o,2021-04-17] for improving a problem, then rejecting all our problems without reading them, then testing the round. - [user:Yousef_Salama,2021-04-17], [user:Mohammad_Yasser,2021-04-17], [user:Noureldin,2021-04-17], and [user:Commando_,2021-04-17] for testing the official contest. - [user:74TrAkToR,2021-04-17] and [user:psevdoinsaf,2021-04-17] for testing the round. - [user:MikeMirzayanov,2021-04-17] for the great codeforces and polygon platforms. This may be the most and only balanced round I've ever set. You'll be given 5 problems...
Codeforces Round #716 (Div.2), platforms. This may be the most and only balanced round I've ever set. You'll be given 5

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15.
By cyand1317, history, 3 years ago, In English
Codeforces Round #487 (Div. 2) Editorial Selamat petang! The curtain has fallen on [contest:989]. Have you enjoyed the problems themselves? Or the stories? Or both? Neither? I hadn't ever intended to create a hard contest, believe me... (╥﹏╥) The author will try to find ways to estimate the difficulty better in the future. Also, stronger pretests, notes taken. Anyways, hope you've all enjoyed the challenges you've faced, and gained something from this round. Congratulations to those who performed well, and commiserations to those waiting for their next chance to shine (^_−)−☆ Below are the tutorials of all problems. Feel free to point out mistakes (if any) or share your ideas in the comments! I might be overcomplicating or confusing something > < [tutorial:989A] <spoiler summary="Short Ruby solution"> ~~~~~ puts gets.codepoints.each_cons(3).any?{|x,y,z|x*y*z==287430}?'Yes':'No' ~~~~~ </spoiler> [tutorial:989B] <spoiler summary="Noam's C++ solution"> ~~~~~ #include <bits/stdc++.h> #define endl '\...
Codeforces Round #487 (Div. 2) Editorial, , and gained something from this round. Congratulations to those who performed well, and commiserations, I hadn't ever intended to create a hard contest, believe me... (╥﹏╥) The author will try to find

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16.
By MikeMirzayanov, 10 years ago, translation, In English
Good news...and not so good news <p> Hi everybody! </p> <p> Okay, we've got good news and bad news. What do I start with? Okay, let's start with the bad news to finish more optimistically. </p> <p> As I was removing the results of some recent vandalism acts (i.e. contribution cheating), I also accidentally removed the results of all your votes :(. I am really sorry and this situation is very unpleasant to me too. We've managed to restore most votes from the backups but the last month has been lost for good. Let me offer my deepest apologies for the incident. I've manually returned the rating to the main page posts, but the votes for other posts and commentaries of the last months have dropped to zero. To soothe the damage somehow, I can stress the popular notion that we are all here to solve problems and discuss the programming and the contribution is not nearly as important. </p> <p> Yet every cloud has a silver lining: the incident has already inspired me to fix the daily backup system which had been malfunctioni...
Good news...and not so good news, Hi everybody! Okay, we've got good news and bad news. What do I start with? Okay

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17.
By JaySharma1048576, 4 weeks ago, In English
Codeforces Round #730 (Div. 2) Hello Codeforces! I am quite excited to invite you to my first ever round, [contest:1543] which will start on [contest_time:1543]. **The round will be rated for participants of Division 2 (having rating strictly less than 2100).** As always, Division 1 participants are welcome to participate in the round but it will be unrated for them. The problems of this round will be themed on the 2005 video game <B><I>Need For Speed: Most Wanted</I></B>. You will be given **5 problems** and **2 hours 15 minutes** to solve them. One of the problems will be **interactive**. So, it is recommended to read the [guide on interactive problems](https://codeforces.com/blog/entry/45307) before the round. I would like to thank - - [user:Aleks5d,2021-07-05] for coordinating the round and not rejecting any of my problems :) - [user:KAN,2021-07-05] for reviewing all the problems and providing invaluable suggestions throughout the round preparation. - [user:mshiladityam,2021-07-05] and [user:ya...
Codeforces Round #730 (Div. 2), Hello Codeforces! I am quite excited to invite you to my first ever round, [contest:1543] which

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18.
By MikeMirzayanov, 3 years ago, translation, In English
Educational Codeforces Round 42 (Rated for Div. 2) Hello Codeforces! On [April 10, 14:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=10&month=4&year=2018&hour=17&min=35&sec=0&p1=166) Educational Codeforces Round 42 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 Div. 2**. It will be held on extented ACM ICPC rules. After the end of the contest you will have one day 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 prepared by me and Alex [user:fcspartakm,2018-04-09] Frolov. We'd like to thank Nikolay [user:KAN,2018-04-09] Kalinin, Grigory [user:gritukan,2018-04-09] Reznikov,...
Educational Codeforces Round 42 (Rated for Div. 2), , Vladimir [user:Vovuh,2018-04-09] Petrov for the testing and help in preparing theround. Good, From the ever present in ACM World Finals city of Moscow, to the new-comer on the world stage city

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19.
By YouKn0wWho, 5 days ago, In English
Editorial of Codeforces Round #735 (Div. 2) The problem names are based on my favorite characters out there. Yes, [problem:1554E] are my most favorite character UwU. I have tried to make the editorials as interactive as possible. Enjoy. [tutorial:1554A] <spoiler summary="Code(C++)"> ~~~~~ #include<bits/stdc++.h> using namespace std; int32_t main() { ios_base::sync_with_stdio(0); cin.tie(0); int t; cin >> t; while (t--) { int n; cin >> n; vector<int> a(n); for (auto &x: a) { cin >> x; } long long ans = 0; for (int i = 1; i < n; i++) { ans = max(ans, 1LL * a[i] * a[i - 1]); } cout << ans << '\n'; } return 0; } ~~~~~ </spoiler> <spoiler summary="Code(Python)"> ~~~~~ import sys input = sys.stdin.buffer.readline t = int(input()) for _ in range(t): n = int(input()) a = list(map(int, input().split())) ans = 0 for i in range(n - 1): ans = max(ans, a[i] * a[i + 1]) print(ans) ~~~~~ </spoiler> [tutorial:1554B] <sp...
Editorial of Codeforces Round #735 (Div. 2), are the best problem solver ever UwU"); return 0; } ~~~~~, in s :\"(", p.first, p.second); } } quitf(_ok, "you are the best problem solver ever UwU

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20.
By kostka, 7 years ago, In English
Hackers ranking (beta) ### FAQ **What is this?** Have you ever wondered who is the best hacker on Codeforces? Here is simple solution, which would try to answer for your problem! I would like to introduce new system of grading hackers in rounds. [cut] <p></p> <b>How does it work?</b> The whole rating system is based on <a href="http://en.wikipedia.org/wiki/Elo_rating">Elo rating</a>. The problem is how to measure user's performance in each round. **Yes, how?** The whole system is now in phase of testing, so some solutions may be changed (and probably will be changed :)). So let's consider some user during some round. Let's call him Bob. **I want to choose another name, may I?** No. **Ok.** So, let's say that Bob solved three problems: A, B and C (Bob is pretty sad), but also hacked one solution for B and had one unsuccessful hack attempt. Bob doesn't know that his solution for C won't pass system tests. How would we know if it was good or bad? At first, we will look at al...
### FAQ **What is this?** Have you ever wondered who is the best hacker on Codeforces? Here, Have you ever wondered who is the best hacker on Codeforces? Here is simple solution, which would

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21.
By Lewin, 6 years ago, In English
Codeforces Round #309 Hello Codeforces! I invite all of you to participate in regular Codeforces round #309 that will take place on [24 June, 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=24&month=6&year=2015&hour=19&min=30&sec=0&p1=166). Some of you may know me as lg5293 on Topcoder (you can see some of my past problems [here](http://community.topcoder.com/tc?module=ProblemArchive&sr=&er=&sc=&sd=&class=&cat=&div1l=&div2l=&mind1s=&mind2s=&maxd1s=&maxd2s=&wr=lg5293)), but this is my first time ever writing a Codeforces round. I've designed all the problems myself and I hope you enjoy them. I want to thank [user:ctunoku,2015-06-23] for helping me come up with stories for the problems, [user:Zlobober,2015-06-23] for his immense help with preparation for this round, [user:winger,2015-06-23] for testing the problems, [user:Delinur,2015-06-23] for translating statements, and of course [user:MikeMirzayanov,2015-06-23] for the superb Codeforces and Polygon systems. I hope to see yo...
Codeforces Round #309, time ever writing a Codeforces round. I've designed all the problems myself and I hope you enjoy

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22.
By MinakoKojima, 8 years ago, In English
Codeforces Round #172 Editorial Overview ... ================== In DIV 1, there are 3 normal tasks accompanied with 2 challenge tasks. About 40 competitors solve first three tasks during the contest and I believe there will be more if we extended the duration a little bit. Task D is a standard data-structure problem hidden behind a classical maximum cost flow model. This kind of problem are usually trick-less, but hard to implement especially under the pressure. Because of this, it becomes tonight's draw-breaker. Task E is a extended version on a classical DP && Math problem. There are many solutions to the original problem, one is giving a global view under the state transition, and using a data structure to handle it carefully. However, this one is even more harder, few people have ever tried it except [user:Jacob,2013-03-11]. (Although is wrong.) As a seasoned competitor, [user:Petr,2013-03-10] took the C-B-A order which proved to be the best choice through out the night. And after quickly solved C and...
Codeforces Round #172 Editorial, to handle it carefully. However, this one is even more harder, few people have ever tried it except

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23.
By drazil, 7 years ago, In English
Codeforces Round #272 Editorial First I want to thank all the problem solvers!<br> Hope you had or are going to have a good time with Dreamoon!<br> If you think there's something that can be improved in this editorial please let me know!<br> Definitions used in this editorial:<br> $\lceil\rceil$ stands for ceiling function.<br> $\lfloor\rfloor$ stands for floor function.<br> $\frac{a}{b}$ stands for real division.<br> For non-negative integer $a$ and positive integer $b$, $div(a,b)$ stands for integral division, $div(a,b)=\lfloor\frac{a}{b}\rfloor$.<br> For non-negative integer $a$ and positive integer $b$, $mod(a,b)$ stands for module operation, $a=div(a,b)*b + mod(a,b)$.<br> $length(string)$ is the length of $string$.<br> For non-negative integer $a \leq b$, $A[a..b]$ stands for the set of $A[a], A[a+1], A[a+2] \dots A[b-1]$ when $A$ is an array and the substring of $A$ consists of $a^{th}$ to $(b-1)^{th}$ character(inclusive) of $A$ when $A$ is a string. For such substring we have $length(A[a..b])=b-...
Codeforces Round #272 Editorial, ) + r2-r1(down\ keys) + c2(right\ keys)$. Note that this is the best answer if the HOME key isever, )$. Note that this is the best answer if the HOME key is ever pressed once, so we won’t consider

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24.
By chinmayajha, history, 4 months ago, In English
My Solution for Problem C : Consecutive Primes (Kickstart Round B 2021) This being my second Kickstart round ever, my 4th month into Competitive Programming (without any prior knowledge), and me being grey, I was proud of myself when I got an approach to Problem C, like within 20 seconds after I read it. So here goes my approach (which also happens to be similar to Kickstart's official analysis for the Test Set 3). UPD : I decided to make a YouTube video fir this question (in Hindi) : So for the solution + approach mentioned below please check the [video](https://youtu.be/oq_cKYdS0MI). #### The Solution - We're given a number N, and we've to find the maximum numnber X less than or equal to N, which should be the product of any two consecutive prime numbers (if that makes sense). - The best way would be to find two consecutive primes near the square root of N. - Let's call the required primes a1 and a2. a1 and a2 are to be assigned to floor value of sqrt(N) and to a1+1 respectively. - This way we get two numbers not necessarily prime near sqrt(N)...
My Solution for Problem C : Consecutive Primes (Kickstart Round B 2021), This being my second Kickstart round ever, my 4th month into Competitive Programming (without any

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25.
By saliii, history, 4 years ago, In English
Codeforces Round #411 Editorial We were waiting several weeks to setting this contest and hope the problem was good enough. #### Events There was a difficulty with [problem:805E]/[problem:804C]. A little bug in the checker fortunately yields accepting an incorrect solution of only one person during the contest. I should apologize all of you because of this. For this sentence, `Vertices which have the i-th (1 ≤ i ≤ m) type of ice cream form a connected subgraph.` You can find the meaning of "connected subgraph" with [connected](http://mathworld.wolfram.com/ConnectedGraph.html) and [subgraph](http://www.edmath.org/MATtours/discrete/concepts/csubgr.html), thus it can be empty as it is more logical. How ever, I should apologize all of the participants because of weak sample tests in the statement. I will write the full editorial in the few next days, now some hints and short solutions exist here. Hints ------------------ [problem:805A] <spoiler summary="hint1"> Almost half of numbers are divisible by two...
Codeforces Round #411 Editorial, We were waiting several weeks to setting this contest and hope the problem was good enough

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26.
By Lewin, history, 6 years ago, In English
Wunder Fund Round 2016 Editorials I hope you enjoyed the contest! Let me know if you find any errors below. Thanks for participating. Short solutions: - Slime Combining: You can just do what's described in the statement. Or, maybe you can do something with the binary representation of the number. - Guess the permutation: Find out where 1 should go. Then, find out where 2 should go, and so on. - Constellation: Start with a triangle and break it up. Or, choose a point and look at angles. Or, sort by x coordinate. - Hamiltonian Spanning Tree: Two cases: X > Y and X <= Y. For X > Y we can almost always avoid the spanning tree edges. For X <= Y we can do something greedy. - Robot Arm: Make a segment tree on segments. A segment is basically just a linear transformation, which can be described with three numbers. - Double Knapsack: Make the problem harder. Let's say I want a consecutive sublist of both lists that have equal sums. Then use pigeonhole principle to get an answer. - Combining Slimes: Use conditional e...
Wunder Fund Round 2016 Editorials, the lines of a "maximum path cover". Restating the problem is a good idea at this point. Here's

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27.
By hmehta, history, 5 months ago, In English
2021 Humblefool Cup w/ $600 in Prizes ### 2021 Humblefool Cup Prelims The fifth edition of the much-coveted Humblefool Cup is here. While we couldn’t host the finals of the 2020 event because of the pandemic and lockdowns during this time last year, we hope to bring you an exciting tournament this year. Topcoder and the Indian Institute of Information Technology (IIIT) Allahabad are excited to bring back the Humblefool Cup Algorithm Match in fond memory of Harsha Suryanarayana <a href="https://www.topcoder.com/members/humblefool"><font color=red><b>[humblefool]</b></font></a>. Harsha is considered to be the best coder India has ever produced. A Topcoder member since 2005, humblefool – as he is known within the coding community –  was a [TCO Finalist](https://www.topcoder.com/community/hall-of-fame/tco/08) twice. Up until his tragic death in an accident in 2014, humblefool was at the top of his game in SRMs and personally trained and motivated many other members. The Humblefool Cup is organized every year to pre...
, Allahabad. The best-ranked student in the qualifying round (not located in India) will be awarded

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28.
By lnishan, 6 years ago, In English
An awesome list for competitive programming! This is a project I started from late January 2016. My motive is that: Although there's fantastic information out there, I think they're still spread all over the place. Therefore, in my opinion it would probably be cool if there's an [awesome list](https://github.com/sindresorhus/awesome) for competitive programming! ( *It's now featured on the main list!* ) I'm actively updating the list here: [https://github.com/lnishan/awesome-competitive-programming](https://github.com/lnishan/awesome-competitive-programming) # Awesome Competitive Programming [![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38d29fed78fa85652e3a63e154dd8e8829/media/badge.svg)](https://github.com/sindresorhus/awesome) A curated list of awesome `Competitive Programming`, `Algorithm` and `Data Structure` resources. Created with a view to connecting people to information, this list below contains a complete collection of all the fantastic resources I've collected over the course of my 11...
by topics. | ☆ | Name | Description | | --- | --- | --- | | ★★★ | [Good Blog Post Resources about

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29.
By NALP, 9 years ago, translation, In English
Codeforces Round #106 (Div. 2) Tutorial [problem:149A] --------------- First, it is clear that if the sum of all numbers $a_i$ is less than $k$, then Peter in any case will not be able to grow a flower to the desired height, and you should output <<-1>>. Secondly, it is easy to see that if we want to choose a one month of two, in which we watered the flower, it is better to choose one where the number of $a_i$ is more. Thus, the solution is very simple: let's take months in descending order of numbers $a_i$ and in these months water flowers. As soon as the sum of the accumulated $a_i$ becomes greater than or equal to $k$ --- should stop the process, the answer is found. [problem:149B] ------------------- In this task required only the ability to work with different numeral systems. Let's try to go through numeral bases, each base to check whether it is permissible, as well as convert hours and minutes to the decimal system and compared with 24 and 60, respectively. What is maximal base, that we need to check? In...
Codeforces Round #106 (Div. 2) Tutorial, bases, each base to check whether it is permissible, as well as convert hours and minutes to the decimal

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30.
By Cirno_9baka, 22 months ago, In English
Codeforces Round #593 (Div. 2) Hello, Codeforces! I'd like to invite you to take part in [contest:1236]. It will held on [contest_time:1236]. The round will be rated for the participants with rating lower than 2100. You will be given **6 problems** and **2 hours** to solve them. Scoring distribution: **500—1000—1000—1750—2000—2500**. The problems of this round were developed by me. Thanks a lot to [user:isaf27,2019-10-16] for his excellent coordination, to Mike [user:MikeMirzayanov,2019-10-16] Mirzayanov for Codeforces and Polygon platform, and to [user:marX,2019-10-16], [user:antontrygubO_o,2019-10-16], [user:NIWIS,2019-10-16], [user:win11905,2019-10-16] for testing. This is my first round ever. I hope everyone will enjoy it. Good luck! **UPD:** The round is over! Congratulations to the winners: **Div.1 + Div.2 participants:** 1. [user:LayCurse,2019-10-17] 2. [user:nuip,2019-10-17] 3. [user:Geothermal,2019-10-17] 4. [user:liouzhou_101,2019-10-17] 5. [user:Pelmelnik2,2019-10-17] **O...
Codeforces Round #593 (Div. 2), ], [user:NIWIS,2019-10-16], [user:win11905,2019-10-16] for testing. This is my firstround ever. I hope

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31.
By Monyura, 6 years ago, translation, In English
Looksery Cup Hello everybody!<br><br> Our company wants to say thanks to Codeforces and congratulate it with the 5 years birthday:)<br><br> A year and a half ago I and the team ([user:Sfairat,2015-01-01], [user:olpetOdessaONU,2015-03-03], [user:Sklyack,2015-03-03]) met Victor Shaburov and became co-founders of [Looksery](http://looksery.com). We work in Computer Vision and Augmented Reality areas.<br> On behalf of all our collective I want to say thanks to [user:MikeMirzayanov,2015-03-03] and Codeforces team, you do a great matter, and I'm sure it will have a huge impact on the IT segment of the nearest future. To tell the truth, I don't know how we would be able to solve the problems that we had at the beginning of Looksery path if there were no Codeforces or ACM ICPC in our lives.<br> I would like to tell a few words about our organization, clarifying my opinion about popular [topic](http://codeforces.ru/blog/entry/17302) of the last few days about competitive programming and "real" job.<br...
of solving the problems, which haven't ever been solved before, are extremely required. Those

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32.
By Nickolas, 9 years ago, translation, In English
Some thoughts about Surprise/Unknown Language Rounds I'm a huge fan of Surprise/Unknown Language Round competition format. Theoretically I enjoy participating in them, but in practice I mostly run them. What's so special about them that makes me like them so much? 1. They are unusual. At some point of time (which arrived pretty soon for me) traditional competitions pall and become a blur. If I give it a thought, I can clearly remember only a couple of the 80 SRMS and CF rounds I've done. The SRM which featured MooresLaw problem (great challenge phase and my only ever room win), TCO elimination round which I passed thanks to a last-minute submission on 500pt, a GCJ round from back when it was held on TopCoder platform, when I got stuck at input parsing and never got to the actual solution... and that's all. Marathon memory is a bit better, probably because I've participated in fewer of them, and each match took more time and effort. But unusual competitions leave the most lasting and vivid impression. 2. They fit my skills....
only ever room win), TCO elimination round which I passed thanks to a last-minute submission, participation (Befunge round, the best one ever, had 340 participants --- any Div2 beats that). However, I, to prepare (which is hard on its own) and less participation (Befunge round, thebest one ever, had

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33.
By Edvard, history, 6 years ago, translation, In English
Educational Codeforces Round 4 Hi, Codeforces! Educational Codeforces Round 4 will take place on [25 December 2015 at 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+4&iso=20151225T1500) for the first and second divisions. You can read about educational rounds [here](http://codeforces.com/blog/entry/21496) and [here](http://codeforces.com/blog/entry/21565). This time a little time has passed since the previous round. Although we planned this round at Monday, we forgot to include it to schedule, so it was appeared only now. So it is the fourth and the last educational round this year. \<Maybe this paragraph will not be changed ever\> The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally. \</Maybe this paragraph will not be changed ever\> This time t...
Educational Codeforces Round 4, round this year. \ever\> The round will be unrated

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34.
By Endagorion, history, 4 years ago, In English
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 ...
Yandex.Algorithm 2017, third elimination round: editorial (with challenges, bells and whistles), . Solution: Suppose that we are allowed to make left circular shifts as well as right ones.

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35.
By hmehta, history, 17 months ago, In English
2020 Humblefool Cup - Prelims Topcoder and the Indian Institute of Information Technology (IIIT) Allahabad are excited to bring back the fourth edition of Humblefool Cup Algorithm Match in fond memory of Harsha Suryanarayana <a href="https://www.topcoder.com/members/humblefool"><font color=red><b>humblefool</b></a>. [Learn More](https://www.topcoder.com/2020-humblefool-cup/) Harsha is considered to be the best coder India has ever produced. A Topcoder member since 2005, humblefool – as he is known within the coding community – was a TCO Finalist twice. Up until his tragic death in an accident in 2014, Humblefool was at the top of his game in SRMs and personally trained and motivated many other members. The Humblefool Cup is organized every year to preserve his legacy and contribution to the Community. 2020 Humblefool Cup Prelims is scheduled to start at [12:00 UTC-5 on March 4, 2020.](https://www.timeanddate.com/worldclock/fixedtime.html?msg=2020+Humblefool+Cup+Prelims&iso=20200304T12&p1=98) Re...
. - The best-ranked _student_ in the qualifying round (_not located in India_) will be awarded $100 prize

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36.
By highonjuice, history, 42 hours ago, In English
Today was the day Practice makes perfect, and blue feels better than green. (Skip to the end if you don't wanna hear an interesting story) A while ago, I made a post about almost being specialist. After a month of getting stuck on pupil, I was starting to think I was not fit to advance in my competitive programming journey. Doubts fell like droplets on a rainy day... But I still practiced... Day after day I would do my daily dose of problems, learning cool new algorithms along the way. Maybe DSU? BFS? DP? Probabilities? Every day I was equipping my toolbelt for the journey. Every day I would challenge myself to a slightly harder task. Although I had to admit, in the back of my head, I was wondering when I will ever use these Data Structures and Algorithms. Then the day came. In today's contest (Round #736 Div1+Div2), I briskly solved A (as I usually do) and took my time on B. (it was implementation, so it was a little annoying). Then I met C. C was an interesting graph problem. I was thi...
when I will ever use these Data Structures and Algorithms. Then the day came. In today's contest

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37.
By low_, history, 2 years ago, In English
First season HNOI Civil War conclusion _Dear Codeforces community,_ Lately, we have successfully organized a high-schoolers' contest: HNOI Civil War. The contest was born as a "rivalry" between two of the best Hanoi-based gifted high schools: Hanoi-Amsterdam High School and Nguyen Hue High School. 3-people organizing committee includes: Trung Lan Nguyen ([user:lantrungseo,2019-07-21]) &mdash; as the Head Organizer, Bao Quoc Ngo ([user:b21quocbao,2019-07-21]) &mdash; as the Head Problemsetter and coach for Nguyen Hue informatics team for this contest, and me, Dung Tuan To [user:low_,2019-07-21] &mdash; as the Head Coordinator and coach for Hanoi-Amsterdam team. ![ ](/predownloaded/0d/47/0d47e43a3a1c387fae35fbfff1e4f54234f72fec.jpg) [cut] . The competition consists of two contests: an Individual-based OI-formatted round and a Team-based ACM-formatted round. You can visit the rounds as information listed below: - **Individual Round One** _(July 14)_: written by low_ and lantrungseo, consists of 4 OI problems:...
: HNOI Civil War. The contest was born as a "rivalry" between two of the best Hanoi-based gifted high

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38.
By stefdasca, history, 3 years ago, In English
Suggestions about Educational Rounds Hello Codeforces! I've been a member of this community for about 1 year and i'm very glad of how things go there, with a single exception: Educational Rounds. Ever since they became rated for div2 users, despite of their rather interesting format, they've proved to be a trap for many users, because of hacking period and contest format(extended ICPC). Basically, as a result, in 99% of situations, problem A, which is supposed to be the easiest one, becomes the most important problem, and this is not exactly good, because in many situations, people who have, let's say ABCD and a rather good penalty, end up getting only BCD but with a bad penalty for 3 problems, just because of a single mere error, while in any other contest they would only have gotten a small drop in standings. Thus, my humble suggestion is to rethink a bit how Educational Rounds(and any ICPC style contest in CF with sorted difficulty problems, like div3 rounds) are working. One of my ideas is to add weight ...
things go there, with a single exception: Educational Rounds. Ever since they became rated, Ever since they became rated for div2 users, despite of their rather interesting format, they've

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39.
By RomeoFantastik, history, 17 months ago, In English
Coronavirus — Overcome the Psychological Stress by Coding My video on the topic: [Shameless Self-Promotion](https://www.youtube.com/watch?v=CFagJwWW7ys) Have you ever noticed how disasters have a weird way of making things better, once the initial problem is contained? Yes, the virus is unpredictable, has deadly potential, and should be of great concern to just about every human on the planet. So, what could possibly be a positive consequence of a life-threatening disease? #### _**1. Code (and live) for the present, not for that offer**_ Yes, these are not the best of times, but a time to reflect on who we are and what is most important in life. For some countries, economy is at risk. But most of Software Engineer jobs give you the opportunity to work remote/from home. Either you have or not a job at the moment, you are not so pressured by this thought anymore. Maybe you come to the conclusion programming is not what you want to do in life anymore. Maybe it's photography, cooking or pottery (Brad Pitt pff..). Or maybe th...
) Have you ever noticed how disasters have a weird way of making things better, once the initial

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40.
By Noureldin, history, 14 months ago, In English
some dull CF statistics: vanishing rating points things to do in quarantine <ul> <li> <s>train to be better at CP</s> </li> <li> <s>get some work done</s> </li> <li> generate some CF statistics </li> </ul> #### vanishing rating points so I ran a python script that collected all rating changes of every rated round and I found some <s>interesting</s> stuff which can be found at the end of blog, however the thing that caught my attention is that rating points are vanishing at a rate of ~5.483 points/round/contestant!!! the average rating change is negative ~ -5.483 points/contestant/round which is weired, you would expect that number to be around zero since the rating system <a href='https://codeforces.com/blog/entry/102'>scales everything</a> so that the sum of ratings of contestants after each round remains the same as it was before the round, maybe a side effect of rounding ? to verify this I compared the sum of rating of all rated accounts against what it should be, there are 258434 accounts that competed in at le...
so I ran a python script that collected all rating changes of every rated round and I found some

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41.
By CheaterCheater, history, 3 weeks ago, In English
The Final Solution | CCB **Having seen too many cheating blogs, it is hard to keep track of all the names and also it annoys people. So how about this, we maintain a common blog for all the cheats ever ?!** **I will update this blog on say a biweekly basis, till then you guys can comment or dm me. Make this blog so famous that even companies/corporates look upto this blog to find if the candidate cheats or not.** **So I have decided to make this a common cheating blog where you will find the list of all the cheaters who ever cheated starting from Round 732. I am determined to cleanse this site and make a little bit of difference are you too ?** **My only request to the reader is too please not treat this blog "as yet another cheating blog" because it is not. It is a collective effort of the community to put a stop to cheating on this site.** **UPD** : **Keeping in mind the blog section of CF and not making look "common cheat blog" which is the first thing you see as it ticks off many people inc...
the cheaters who ever cheated starting from Round 732. I am determined to cleanse this site and make a little

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42.
By neal, 3 years ago, In English
How randomized solutions can be hacked, and how to make your solution unhackable Hi Codeforces! In Round 507 earlier today, a large number of "mostly correct" randomized solutions on [problem:1039B] were hacked. I wanted to write a quick explanation of how it's possible to hack these, as well as a guide on how to write your code so that you aren't vulnerable to getting hacked. First to go over the solution quickly (skip down a few paragraphs if you already know the solution): one can use binary search to reduce the range of possible locations for the train to a constant multiple of $K$, such as $6K$. Just make sure to expand out both ends of the range by $K$ after every iteration. Once the range is at most $6K$, one can repeat the following: 1) Make a random guess out of the remaining numbers. The probability of success is at least $\frac{1}{6K}$. 2) Binary search again until the range is at most $6K$ again. It turns out this only takes one query, since after our previous guess our $6K$ range will become an $8K$ range, and a single query will reduce this t...
Hi Codeforces! In Round 507 earlier today, a large number of "mostly correct" randomized solutions

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43.
By Nickolas, 9 years ago, translation, In English
Surprise Language Round #6: editorial Roco is a very simple language. On one hand, it's esoteric, so everything you need to know about it fits in two pages. On the other hand, it's powerful enough to enable writing rather complicated programs in it without racking one's brains over each elementary operation (like in Brainfuck). Being able to refer variables using names (numerical, but names nevertheless) is already a gift to the programmer :-) #### [problem:188A] As usual, the first problem tests the competitor's understanding of basic arithmetic operations. The solution is very similar to the example. ~~~ iin [0] mul [1] [0] 2 dec [1] mul [1] [1] [0] iout [1] ac ~~~ Starting with the second one, the problems need learning the main feature of the language --- the coroutines. [cut] A coroutine is a named piece of code executed in an endless loop. Something in between a procedure (without input parameters and variables, but with a name used for calling it) and a loop (without loop counter or break cond...
Surprise Language Round #6: editorial, to add the second number to it ever since the example). There are two ways to do this: either read, to it ever since the example). There are two ways to do this: either read the number as a sequence

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44.
By ko_osaga, history, 4 years ago, In English
Facebook Hacker Cup 2017 Final Round ![ ](/predownloaded/88/d0/88d0ee9433d1160fc97487edb5c61e82c9f06e78.jpg) Round : https://www.facebook.com/hackercup/scoreboard/1799632126966939/ Time : https://www.timeanddate.com/worldclock/fixedtime.html?msg=2017%20Facebook%20Hacker%20Cup%20Finals&iso=20170614T1330&p1=234&ah=4 List of Participants : http://codeforces.com/blog/entry/50089 (Note that actual participants slightly differ from that list) I'm pretty flattered for my first ever onsite competition (beside IOI) :D Good luck and have fun!
Facebook Hacker Cup 2017 Final Round, from that list) I'm pretty flattered for my first ever onsite competition (beside IOI) :DGood, I'm pretty flattered for my first ever onsite competition (beside IOI) :D Good luck and have fun!

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45.
By Nisiyama_Suzune, 4 years ago, In English
[Tutorial] Math note — Möbius inversion If you've ever taken some lessons on competitive programming, chances are that you have already heard about one of the most famous formula: the Möbius inversion. This article is aimed to provide some basic insight on what is the Möbius inversion, as well as how to apply it in various programming tasks. Prequisite ================== If you are not familiar with the linear sieve and multiplicative functions, it is recommended that you read about them first [here](http://codeforces.com/blog/entry/54090). I will introduce some frequently used notations and lemmas first. Notation ------------------ 1. $[P]$ refers to the boolean expression, i.e. $[P]=1$ when $P$ is true, and $0$ otherwise. 2. $\lfloor x \rfloor$ refers to rounding $x$ down to the nearest integer. Thus $\lfloor \frac{q}{p} \rfloor$ refers to the integer division. 3. $d|n$ means that d can divide n (without a remainder). The following functions are all multiplicative functions, where $p$ is a prime numbe...
If you've ever taken some lessons on competitive programming, chances are that you have already

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46.
By Nickolas, 9 years ago, translation, In English
What is it like to be a problem writer? A couple of days ago I was asked to answer the question "What is it like to be a problem writer for programming competitions?" at Quora web-site. My first idea of the answer had only one word, but then I've thought of a more detailed one, and then of a story I must include, hmm, and I should definitely mention this... Around the second page I realized that this is becoming more than an answer, and at the third one I decided to share this article with a qualified audience --- that would be you. So, what is it like to be a problem writer for programming competitions? In one word (the one I've thought of at first), it's "awesome". In a bit more detail, "hard, sometimes unrewarding, but anyways fascinating job". In even more detail... [cut] First of all, inventing problems is more interesting than solving problems invented by other people --- otherwise problems for tournaments and regular contests would be written by contest organizers only :-) The author is more important for th...
, and conversations about which round is mine and is it at all became routine, but it lasted for agood

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47.
By SecondThread, history, 13 months ago, In English
CFNotifications.com: Hear verdicts to your submissions! (no set up required) CF Notifications ================== Want an easy-to-use tool to notify you when you get a problem correct? Looking for an inspirational jingle to celebrate when you AC? Wish you could just move on to problem B immediately after submitting A and had someone to let you know in case you got it wrong? Now you can! [CFNotifications.com](http://cfnotifications.com) is a simple website that does this for you. All you have to do is type in your handle and click login. ![ ](http://wumbogames.github.io/cfPictures/CFNotificationsLoginScreen.png) It works on all CF rounds, and also other submissions if you are upsolving, practicing, or running a VP on your own. Personally, I just leave it on a second computer with the volume turned up and then I don't have to worry about it ever. ### How it works It rechecks Codeforces every 4 seconds for new submissions, or every 1 second if you have a submission that is judging. It uses the CF API and I did my best to make sure it is as low-impa...
it on a second computer with the volume turned up and then I don't have to worry about itever

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48.
By Sazzon, 5 years ago, In English
A Competitive Paradox. Hi everyone! Recently I've been taking notes on my behavior during contests (It can be some round here in Codeforces, Hackerrank or even at ACM-ICPC sub-regionals) and trying to come up with a way to setup my brain to perform well. Sad thing is: **I get too nervous** . My first attempt in a competitive envoriment was in 2014, an Brazillian ACM-ICPC sub-regional (not a very intense envorioment as you may guess). I was there, me and my colleages. No hopes on getting a good place. Just for fun. Trying my best to prove something to someone, I don't know. For our surprise, we came in 4º out of 31 teams. That was a great result for our first try! But one year later, with other teammates (better ones, in my opinion!) and after one entire year of intense studying (I was definetly more prepared) we came in 5º place. I was personally devastated. I couldn't pass even the easy ones, my teammates helped a lot and basicly carried me entirely. Also I'm on a streak of highs and lows on contes...
round here in Codeforces, Hackerrank or even at ACM-ICPC sub-regionals) and trying to come up with a way

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49.
By aryanc403, 6 weeks ago, In English
Power series on sets? (Added one example) Update 2 &mdash; Thanks ~adamant,2021-06-25 for his [Subset convolution interpretation](https://codeforces.com/blog/entry/92153) blog. It does simplifies a lot of things. Update 1 - Let's consider this problem - We have a function `subset_convolution(A,B)` it gives us [Subset Sum Convolution](https://codeforces.com/blog/entry/72488) of two sets $A, B$. Let's say we array $A$ with $A[0]=1$ and we want to find `A^K` defined as $A$ convoluted with itself $K$ times. `A^2 = subset_convolution(A,A)` `A^3 = subset_convolution(A^2,A)` ... `A^k = subset_convolution(A^{k-1},A)` The best I can think right now is using something on lines of fast exponential to achieve $O(log K*N^2*2^N)$ time where $2^N$ is the size of A. Also, there exist some solutions $O(N^3*2^N)$ using the fact that the majority of the multiplications will be with A[0] and permutations & combinations. But it can be done in $O(N^2*2^N)$ using tricks well known at some pla...
= subset_convolution(A^{k-1},A)` The best I can think right now is using something on lines of fast

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50.
By zerocold, 8 years ago, In English
FaceBook Qualification Round Solutions 2014 **1. Square Detector (20 Points)** When facing a problem in a programming contest there are three main things to consider when planning your solution. In order of importance: **Is the algorithm correct.** **Is the algorithm fast enough.** **Is the algorithm easy to implement.** In this particular problem the first two points are rather straightforward, the task is conceptually simple and with the small input size efficiency is not a big concern. The third point however deserves some consideration, I'm sure you are well aware that it's easy to make bugs in any piece of code you write, and chances for having bugs increase sharply with the code lengths and complexity. That's why it's worth to spend couple extra minutes to think about an approach that yields the least complicated code. One clever way of solving this is to realize that if you take the bounding box of all the black cells all you need to check is that it's a square and that all the cells inside it are black. Si...
FaceBook Qualification Round Solutions 2014, consideration, I'm sure you are well aware that it's easy to make bugs in any piece of code you

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51.
By imachug, history, 2 months ago, translation, In English
Let's face it, Polygon is horrible ![image](https://i.ibb.co/rs7PwmM/7Cu9Z.jpg) Polygon is not world's greatest evil. Polygon doesn't even have a particular defect that makes it horrible. You can't say what's exactly wrong with Polygon. Polygon seems to work, it seems like every feature is supported, but if you touch it here it will fall apart, and if you touch it there a problem (pun not intended) will appear. Or not, depending on your luck. Polygon is like PHP. For those who haven't read the famous rant, I'll cite it for you: > I can't even say what's wrong with PHP, because-- okay. Imagine you have uh, a toolbox. A set of tools. Looks okay, standard stuff in there. > > You pull out a screwdriver, and you see it's one of those weird tri-headed things. Okay, well, that's not very useful to you, but you guess it comes in handy sometimes. > > You pull out the hammer, but to your dismay, it has the claw part on both sides. Still serviceable though, I mean, you can hit nails with the middle of the head holding it...
one of those weird tri-headed things. Okay, well, that's not very useful to you, but you guess

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52.
By Nickolas, 16 months ago, translation, In English
April Fools Day Contest 2020: editorial _This was the most well-attended April Fools Day Contest in the whole history of them: 10343 participants solved at least one problem! It was also fairly well-balanced: while each problem has been solved by at least 200 participants, only 17 of them solved all 8 problems._ ##[problem:1331A] This was the consolation problem of the contest, and still a lot of participants asked me for hints on this problem &mdash; some even before the beginning of the round! If you're still not sure how to solve it, the contest announcement itself promised that the contest is not rated, so the answer is a resolute ``NO'' (case insensitive, quotes for clarity only) :-) ##[problem:1331B] Unusually for this type of contests, the second problem had an actual problem statement! The real task was hidden in it using Steganography 101 &mdash; the first letters of the lines spelled out "TWO FACTORS". [cut] A quick look at the examples confirmed that you needed to factor the given number and print ...
_This was the most well-attended April Fools Day Contest in the whole history of them: 10343

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53.
By manishbisht, history, 5 years ago, In English
Google Code Jam 2016 (Registrations Started) ![ ](http://www.letsintern.com/blog/wp-content/uploads/2016/03/Code-Jam-2015.jpg) Google Code Jam is back !! For the 13th year, they are calling all programmers to put their skills to the test in multiple online rounds of intense, algorithmic puzzles. And for the second time, they are looking for those who want to code in a distributed environment, too. Distributed Code Jam is back and better than ever, with an additional online round and larger grand prize. Do you have what it takes? **Code Jam 2016 Registration is now open!** [Register](https://code.google.com/codejam/contest/registration) before the Online Qualification Round on April 8 at [23:00 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?p1=0&year=2016&month=4&day=8&hour=23&min=0&sec=0). What’s involved in Code Jam: - A 27-hour Online Qualification Round taking place on April 8, 2016 @ [23:00 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?p1=0&year=2016&month=4&day=8&hour=23&min=0&sec=0). - Mu...
is back and better than ever, with an additional online round and larger grand prize. Do you have what, than ever, with an additional online round and larger grand prize. Do you have what it takes

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54.
By BYN, 7 years ago, In English
Elimination Round — Bayan programming Contest 2014-2015 Elimination Round will start today, [14:30 (UTC)](http://www.timeanddate.com/worldclock/fixedtime.html?day=19&month=10&year=2014&hour=14&min=30&sec=0) and only contestants who have passed Qualification Round will be eligible to participate. Score for each solved problem is calculated based on these values: - n = No. of accepted submissions - t = Contestant's submission time - p = Number of contestant's wrong attempts ![ ](http://bayanbox.ir/id/946335599772681293?view) To receive the latest news fast, follow us on twitter: [@bayan](http://twitter.com/bayan) **Update 1:** The Elimination round is over, and let's face it: It was far from good! Yes, we're aware of all the issues, and we know that nothing is more nerve-racking than facing those issues during a competitive contest. So, first thing first, we'd like to sincerely apologize for all the inconveniences caused. In last hours, we thought that the contest has become too hard, so we made a major wrong decisi...
Elimination Round — Bayan programming Contest 2014-2015, :** The Elimination round is over, and let's face it: It was far from good! Yes, we're aware of all

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55.
By Psyho, history, 6 years ago, In English
Slides from my BubbleCup presentation: "How to extract maximum value out of competitive programming?" Last week there was a [BubbleCup contest](http://codeforces.com/blog/entry/19957), where I was invited as a guest and gave a presentation. AFAIK the presentation was recorded, but I have no idea if it's going to be released (or when). The presentation itself, is probably the worst presentation I ever gave. I talked mostly about how confusing it's going to be, but I was the one confused there :) Anyway, here's the [link](https://www.dropbox.com/s/h4urgpxldfdp00y/Psyho%20presentation.pdf?dl=1) to the slides. I still think it might be useful for some people, since it touches something that is very rarely talked about. The presentation itself was made to counterbalance all of the simple answers to the old question of "How to get better in competitive programming?". My main points (that I don't think were made clear enough): - It's better to train to be an all-rounder than to have a narrow specialization. Especially in the long-term. People very often change the area of interest. ...
ever gave. I talked mostly about how confusing it's going to be, but I was the one confused

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56.
By SecondThread, 12 months ago, In English
1<<12 Sub Live Stream! TLDR: [Stream at this time](https://www.timeanddate.com/worldclock/fixedtime.html?day=8&month=8&year=2020&hour=12&min=30&sec=0)! See you there! Hi everyone! I very recently reached 1<<12 subscribers on Youtube! To celebrate, I'm going to be doing my first ever livestream! I'll be on Youtube only this time (maybe I'll do both youtube and twitch later if there's demand for it). The stream will include looking at and trying to solve Code Jam Finals problems, which will be going on at the same time. **In general, live-streaming participation in a contest is considered cheating and is very bad. Do not do this for any public contests!** To be careful not to leak solutions or anything: 1. I will significantly delay my start of the round. 2. I will spend the beginning of the contest (where my participation overlaps with the real thing) reading all problems instead of solving. 3. I will not explain solution ideas of any problems until the round is over. That way, this isn't any mo...
subscribers on Youtube! To celebrate, I'm going to be doing my first ever livestream! I'll be on Youtube only

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57.
By Pancake, 8 years ago, In English
CodeForces Improvement : Should tutorials be obligatory ? Hello CodeForces Community. There's no doubt about the importance of having a good problems' analysis after programming contests. I am disappointed about the Rounds Tutorials (and I think many others are) because of the following reasons : - They don't necessarily exist for some recent contests :-/ - If they existed , then in many cases I encountered the following situations : 1. Written partially or totally in Russian. 2. Written in ambiguous English. 3. Written "unofficially" , i.e some user who participated in the contest decided to share his ideas. This might be inconvenient because the methods he used can be different from the intended solutions which are generally more elegant. 4. Not complete. Solutions for some problems are missing with a promise of adding it "soon". This "soon" often turns into "never". - If none of the previous problems occurred , then sometimes I feel that the tutorial is disappointing because it's not discussing any of t...
of the best competitive programming platforms ever created , and I enjoy participating. While I think, the website. I think CF is one of the best competitive programming platforms ever created , and I enjoy

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58.
By Shisuko, history, 2 years ago, In English
The Intuition Behind NIM and Grundy Numbers in Combinatorial Game Theory There are already many wonderful resources online for learning the basics to combinatorial game theory, but the intention I have for _this_ guide in particular is to try to make them more intuitive. Why does XOR work for Nim? Why does mex produce the Grundy numbers? When it was taught to me, it was more or less just as 'magic' to memorize, but now I think I have a decent understanding of why they are true, so now that I have a grasp of the intuition behind it, I decided I should record my thoughts into a blog. Nim games ================== Suppose we are playing a Nim game. As we know, Nim games usually follow this sort of template: - There are $n$ piles of stones, and each pile contains $p_1, p_2, p_3, \cdots p_n$ stones, where each of the $p_i$ is some nonnegative integer. This collection of piles defines our game state. - There are two players who take turns removing stones. The current turn player may remove as many stones as they wish, so long as all the stones come f...
one pile at a time, so it seems like a good idea to get some information from each pile, then find

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59.
By yevhenii_kanivets, history, 4 months ago, In English
Codeforces WatchR 1.9.0 (Doyle): Authentication flow Hey, Codeforces! Since the last November, we've been off, but now we are back with a lot of cool stuff, so here is the update on what's new in Codeforces WatchR apps in [App Store](https://apps.apple.com/us/app/codeforces-watchr-contests/id1495591299) and [Google Play](https://play.google.com/store/apps/details?id=com.bogdan.codeforceswatcher). ![ ](/predownloaded/77/80/77803e14639f3d3035be0c2e82cfdadf85c91cea.png) Business-logic is moving to backend ----------------------------------- We introduced the backend two milestones ago, but only the "Newsfeed" feature was implemented before now. Other features were still handled directly by mobile apps using [Codeforces API](https://codeforces.com/apiHelp), which made them complicated and unstable in some cases. In particular, fetching followed users rating updates required many requests (one per user) whenever the user tried to refresh the list. It wasn't really scalable and stable enough, so the user experience was rather daun...
as well (Google, Facebook, Apple, etc.). Please, note that it's not your Codeforces account, and we

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60.
By cpforfunCmnt, history, 6 months ago, In English
RATING MATTER OR NOT!!! Why cheating has increased in recent times?? Short answer:**NO** _Long answer_ : Hey coders if you are new to programming then I let you know `competitive programming is a sport ` which people do for fun . Now come to the biggest issue `CHEATING IN CODING CONTESTS!! and thirst for High rating` **Youtubers and many people ** are making beginners believe that good rating and high star will make your chance higher for getting into xyz companies. **But is this reality?** **No...Actually a big no** Never ever has high rating benifited you in placements.Yeah some people will tell you that high rating will provide you referals ,but if you are freshers then referal is going to do nothing help in your hiring rounds. **Okk now so Why coding? What is the perks of doing cp??** First of all cp is not for those who want to _showoff their rating among friends_ Cp is fun.Whenever I give contest and get AC on comparatively harder question,it give me big dopamine boost.And this is not the only reason for me to do cp.Li...
** are making beginners believe that good rating and high star will make your chance higher for getting

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61.
By Karan2116, history, 5 years ago, In English
Everything About Dynamic Programming **I decided to gather some good material on the web related to DP and found some good explanation by svg on topcoder forums..Hence wrote this blog.Will format it when i get time.** ![ ](http://codeforces.com/predownloaded/2c/af/2caf058ab9cf6db0f875c573fb0d6e73de572122.png) **Problem:** About 25% of all SRM problems have the "Dynamic Programming" category tag. The DP problems are popular among problemsetters because each DP problem is original in some sense and you have to think hard to invent the solution for it. Since dynamic programming is so popular, it is perhaps the most important method to master in algorithm competitions. The easiest way to learn the DP principle is by examples. The current recipe contains a few DP examples, but unexperienced reader is advised to refer to other DP tutorials to make the understanding easier. You can find a lot of DP examples and explanations in an excellent tutorial Dynamic Programming: From novice to advanced by Dumitru. The purpose ...
**I decided to gather some good material on the web related to DP and found some good explanation

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62.
By Lost_Arrow, 9 months ago, In English
C++20 — Features and Introduction Some of you may remember me from a [recent blog](https://codeforces.com/blog/entry/84162) of mine regarding the request for the addition of the [GCC 10.2.0](http://winlibs.com/) compiler for the partial support of [C++20](https://www.wikiwand.com/en/C%2B%2B20). I mentioned in the blog that if enough people wanted to know more then I'd write a simple tutorial on it, and so here it is! Thank you to everyone who reached out on PMs and my friends on Discord. Keep in mind that I'm not very experienced with all aspects of C++20 or even pre-C++20 to be able to show the usage of every possible feature and probable effects on CP. I'm learning and discovering new things everyday and you can consider this as my personal overview and summary of it; which beginners like myself can make good use of to explore new concepts in programming. Feel free to add comments about anything I've missed (which is undoubtedly a lot) and I'll update the blog to summarise as much as I can (ofcourse, with your ...
consider this as my personal overview and summary of it; which beginners like myself can makegood use

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63.
By ItsNear, 10 years ago, translation, In English
TCO 2011, days 2 and 3 <p>TopCoder Open 2011 keeps going.<br /><br />Yesterday we were supposed to hold a poker tournament with a grand prize MacBook Air. There were a lot of people willing to participate, which forced us to split the tournament into two elimination rounds and one final. Out of 16 people who registered for the tournament, 8 were russian-speaking, and all of them appeared to be in the same elimination round. Petr and MikhaelOK advanced from that round, while 7ania7 and theycallhimtom advanced from another one, which was non-russian-speaking. Unfortunately I don't have any pictures of the elimination rounds, however, we played more poker that day, in the same place, so this picture gives you pretty good understanding of how it looked like (during the elimination round it was a little bit more crowded though):<br /> <span> <img alt="" border="0" height="449" src="http://content.foto.mail.ru/bk/shd/_blogs/i-626.jpg" width="600" /> </span> <br /><br />Last time I didn't publi...
to the onsite round, in which people were offered to come up with an idea of a good event for competitors, good understanding of how it looked like (during the elimination round it was a little bit more

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64.
By myblog, 8 years ago, In English
toms online Many amateur won't instantly comprehend the necessity for selecting the right list of gambling fight sneakers. However, when you are getting more pragmatic information, you will end up conscious the stress using your calves increases your present need to rich person sneakers that has a respected clutches. This particular form is vital to possess without shedding mobility or knowledge to come up with quick, rapid techniques. You'll be needing these sneakers to offer you helping jointly comfort, like you can inside a unique form of sporting activities shoe. You may also ought to keep added troubles involving safety in your thoughts overly. Whenever you last comprehend the main benefit of having efficaciously the installation of wrestle shoes and also footwear, then you'll definitely be able to find the suitable shoes or boots for the following opt for. ![ ](http://www.tomsaustralia.net/images/tomsaustralia/Stripe%20Classics(M)/stripe-classics-mens-navy_2.jpg) Despite the fact ...
" border="0"> Among the many all round capabilities just about exhausting grapple footwear aswell

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65.
By Nickolas, 9 years ago, translation, In English
Challenge24 2012 — Finals Challenge24 finals are finally over, and as usual, I hurry to share my impressions about them. The impressions are sponsored by team Progopedia (Andrii Maksay a.k.a. [user:maksay,2012-05-03], Sergii Dymchenko a.k.a. [user:kit1980,2012-05-03] and me). Such things are the best to write immediately after the contest, while the emotions still invade you. Of course, one can start writing them while still in the competition (and last year I did so --- I was pretty useless at night anyways), but this year we felt alert and fought for the points till the last minutes of the contest, so the blog post was postponed. The main part of Challenge 24 took a bit less than 48 hours: registration and optional sightseeing on Friday, the round itself from Saturday morning to Sunday morning, and winners announcement and closing ceremony (for the toughest contestants who don't really need all that sleep) on Sunday noon. [cut] We arrived on Friday mid-afternoon, and went to the university immediatel...
keeps, the online round won't be easy anymore, and a team without three reds in it might aswell save

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66.
By AnshAryan, history, 15 months ago, In English
Scaler Academy: Our side of the story: AMA Hello folks, My name is Anshuman and I am the co-founder of Scaler Academy and InterviewBit. I am a competitive coder myself, since 2006, been a part of Codeforces since 2009, when Beta rounds were happening. Been to ACM ICPC World Finals twice. Ex-Facebook where I was one of tech leads on the messages and messenger team. I believe every company/program gets criticism and it should only be taken constructively. While most of the blogs here on Scaler Academy have been very far from truth, I never came to respond here because it’s hard to reason with anonymous fake accounts. However, the past few days, these folks have started harassing and abusing current Scaler Academy students and mentors. They created a phishing website clone of ours to steal student credentials. They have bullied anyone who has tried to express their opinion if it was positive towards scaler. **That, in my dictionary, is online bullying and very unethical.** Attaching images of students and mentors wh...
speaking very openly against us. Ask him if he ever got a negative message from our end

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67.
By Nickolas, 10 years ago, translation, In English
TCO 2011 as seen by a blogger, p.2 <a href="http://codeforces.ru/blog/entry/2788">Part 1</a> <br /><br /> My further narration becomes less sequential and consistent than the first part. This is mostly due to the fact that competition rounds themselves are covered in the official blog (not to mention that I haven't followed all of them from start to finish), so I'll focus on the interesting things which were happening between the rounds, after them and sometimes even instead of them :-) <br /><br /> At the end of July TopCoder Studio ran a <a href="http://studio.topcoder.com/?module=ViewContestDetails&amp;ct=30022930">contest</a> to get some ideas of how to entertain people at the onsites. The voting for the ideas had a very poor interface (I wonder whether there was a single person who has read all the ideas before voting?), but still it allowed to choose four ideas: <br /> [cut] <br /> 1. Football game. Originally it was supposed to be a real football game, but it turned out to be tricky implementation-wise, so it was...
it was replaced with an Xbox game. The best thing I can say about this idea is to stay silent about

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68.
By MikeMirzayanov, 7 years ago, translation, In English
ACM-ICPC World Finals 2014: Before Opening Ceremony Oh yes! Only a few days left before the Championship finals! The teams have already gathered in Yekaterinburg, most of them have registered and are watching a game between Russia and Belgium. I want to start from some history and remember that the tradition to publish travel notes about Saratov State University's trips to finals started back in 2005. The regular pattern is that almost every year when we made notes, our team won a medal. I won't try my luck, so here are some of the first impressions of this year. [cut] The Codeforces community knows this year's team very well, its members are: * [user:Gerald,2014-06-23] &mdash; Gerald Agapov, a person who coordinates Codeforces problems. He has been the key person collaborating with problem authors for Codeforces rounds since 2012. Oh yes, if something goes wrong with problems, he is the one I beaker at, but the guy is great and we hardly ever hae any problems :-) Gerald isn't only into programming. He loves maths, magnifi...
impressions of this year. [cut] The Codeforces community knows this year's team verywell, its

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69.
By Xellos, 8 years ago, In English
Codeforces Trainings Season 1 Episode 10: Editorial #### **Welcome to The Editorial!** <img src="http://th04.deviantart.net/fs70/PRE/f/2013/078/b/f/mi_super_saiyan_god_remasterizado_by_salvamakoto-d5ymxyi.png" height="50%" width="50%" /> **Keep the upvotes piling up! muhehe** IZ.COMPLETE. ### A. Rasheda And The Zeriba [cut] $\ $ (difficulty: medium) The first question is: When is it possible to construct a (convex) polygon from sticks of given lengths $L_i$? This question is answered by what's sometimes known as Polygon inequality theorem, which states that the sufficient and necessary condition is for every $L_i$ to be strictly less than the sum of all other $L_i$. You can imagine that it works because for the endpoints of every side, the shortest path between them (equal to the length of that side) must be smaller than any other path, including the other one along the perimeter of the polygon; constructing such a polygon, even a convex one, is pretty easy, just imagine it as having sticks linked to each other that...
involving maximum/minimum edges, it's best to use a union-find data structure. That's because if we sort

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70.
By SebasJM, history, 3 years ago, In English
Advice about where you compile your code Today, the CF Round #465 ocurried. Imagine you have some time to participate in a contest but you are not using the computer you always use (for example, a work's borrowed laptop). You enter to Ideone and code your solutions. Suppose you solve some problems. It seems to be a regular round. When the contest is over you receive one message: ![ ](https://i.imgur.com/cpViHHn.jpg) **So, "what happened??" I thought.** Well, some mediocre person was updating the "Recent Codes" page of Ideone, looking for solutions to steal from a distracted and naive guy. This is the cheater's profile/submissions: http://codeforces.com/profile/iwillwintoday As you can see, he copied identically my today's two submissions: http://codeforces.com/submissions/SebasJM You can see that I've been using this template since months ago. This post is not about excuses, but about lessons. So, I have two things to say: **To the community:** This is a basic and well known advice, but is always goo...
Today, the CF Round #465 ocurried. Imagine you have some time to participate in a contest

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71.
By MikeMirzayanov, 12 years ago, translation, In English
Memories: ACM-ICPC World Finals 2009 <p> <img src="http://lh6.ggpht.com/_mSdPzSw5zAo/S2KKSsTdWyI/AAAAAAAADGE/vpMUDSuenS0/IMG_0494.JPG" style="float: left;margin: 1.0em;"> The World Finals of the 33rd International Collegiate Programming Contest for was held in the capital of Sweden, Stockholm. The contest was held in Europe for the third time: in 1999 it was held in Eindhoven (the Netherlands), in 2004 - in Prague (the Czech Republic). It was the first time the key role in the competition had been played by the University: it was held in the library of the Royal Technological University. One hundred best teams of the world took part in the final, while the preliminary rounds saw 7109 teams from 1838 Universities and 88 countries competing. It was the sixth time the Saratov State University had took part in ACM-ICPC World Finals. </p> <p> The participants were placed in two hotels in the historic centre of Stockholm, Gamla Stan district. Our team was placed in the Gran...
hundred best teams of the world took part in the final, while the preliminary rounds saw 7109

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72.
By beka00, history, 3 years ago, In English
An awesome list for competitive programming! This is a project I started from late January 2016. My motive is that: Although there's fantastic information out there, I think they're still spread all over the place. Therefore, in my opinion it would probably be cool if there's an awesome list for competitive programming! ( It's now featured on the main list! ) I'm actively updating the list here: https://github.com/lnishan/awesome-competitive-programming Awesome Competitive Programming Awesome A curated list of awesome Competitive Programming, Algorithm and Data Structure resources. Created with a view to connecting people to information, this list below contains a complete collection of all the fantastic resources I've collected over the course of my 11-year competitive programming career. I hope you'll find it useful :) What is competitive programming? — Quora Contributing Please kindly follow CONTRIBUTING.md to get started. You can also contribute by sharing! Share the list with your classmates, your friends and eve...
. One of the most well-crafted team notebooks (contest libraries) I've ever seen. ★★☆ jaehyunp

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73.
By Xellos, 7 years ago, In English
USACO 2013/14: March Contest Note that this weekend (Friday 7.3. to Monday 10.3. inclusive, $\pm$ time zone), this year's last round of USACO (before US Open) takes place. You'll be able to access the contest from [the USACO page](http://usaco.org/). Registration is required. Feel free to discuss the problems here [after the contest ends](http://www.timeanddate.com/worldclock/fixedtime.html?iso=20140311T16) <s>(which is, btw, not very clear, because there are no official start/end times posted &mdash; around Tuesday afternoon in UTC)</s>. I'll probably also post my solutions here. Also notice how similar this is to my blog post about COCI :D. This is one of the usual Crazy Weekends &mdash; there's COCI, USACO and start of the Codechef Long Challenge. It's like the contest organizers do this on purpose... <b>UPD: The [results](http://usaco.org/index.php?page=mar14results) are up now! **UPD**: Negative votes... trolls growing strong here! **UPD^2**: Trolls are gone now. Lol. **UPD ** ### Solu...
round of USACO (before US Open) takes place. You'll be able to access the contest from [the USACO

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74.
By Tarrus, history, 3 years ago, In English
Invitation to Exun 2018 Programming Prelims Greetings!
 Delhi Public School R.K. Puram is hosting Exun 2018, the 23rd iteration of the annual tech festival on October 27 and October 28 this year. The event is being hosted under the aegis of the Digital India initiative and will be national for the first time ever! We will be providing free accommodation to participants (and accompanying teachers) from 27th to 28th of October. To get more details regarding the same, you can visit our [website](https://www.exunclan.com/). The preliminary round for the programming event will take place on 3rd October on the codechef platform from 5 pm to 8 pm. The contest will be unrated and will consist of 5 problems, with difficulty ranging from Easy to Medium-Hard. A rough idea of the topics covered can be obtained from the [Advanced CodeChef Scholarship Syllabus](https://www.codechef.com/certification/prepare#advanced-syllabus). In order to be eligible for the onsite finals, one must register [here](https://exunclan.com/reg/crossreg.php). ...
of the Digital India initiative and will be national for the first time ever! We will be providing free

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75.
By dotorya, history, 4 years ago, In English
Round #421 was awesome! It was my best round in Codeforces **"EVER"!**
Round #421 was awesome!, It was my best round in Codeforces **"EVER"!**

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76.
By Archazey, 6 years ago, In English
CF round 292 - Weird rating update Hey,I took part in round 292 div 2 and luckily I got a good place (for me) ,and this is 246. But sadly when I looked 1 hour ago on rating update,I saw that my rating was lower,and it says that I took place 500+ as you can see on my profile. Here is my proof : http://tinypic.com/view.php?pic=3538l8k&s=8 , or you can look on standings page 3 (places ranging from 200 to 299). I want to know if anyone has ever had this problem and if this can be solved... Thank you :D
CF round 292 - Weird rating update, Hey,I took part in round 292 div 2 and luckily I got a good place (for me) ,and this is 246

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77.
By jjang36524, history, 23 months ago, In English
I suggest some type of contest. If there are these types of the contest, I think codeforces would be more interesting. 1. hackforces. This type of contest has absolutely zero pretest and weak system test. Some wrong code may get right if there is no hack. (Maybe no uphacking update would be good) 2. the G takes it all. The point of the problem would grow like 100 400 1600 6400 25600 102400. Exponentially. Who only barely solved g wins against who solved a~f in fast time. 3.Speed! The point of the problem reduces by half in 30 minutes. The first to the tenth solver of each problem would get the increased point. 4. The shortest round ever. Contest time would be 30 minutes, no reducing points for time, and LOTS of implementation problem! Who is the fastest typer in the world? Dear [user:MikeMirzayanov,2019-08-23]
. The shortest round ever. Contest time would be 30 minutes, no reducing points for time, and LOTS

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78.
By fizzywater, 9 years ago, In English
It's Time to Practice! For the last few years I've been getting involved in the ICPC at both of my universities (UC Davis and UC San Diego). Since I was born in 1990, the 2013 ACM ICPC is the last regional competition I'll ever be eligible for, and I've decided to give it my all! I've committed to practicing a little bit each week, which honestly fun in it of itself, so why not? So far I've competed in two contests on CodeForces and one on TopCoder. In CodeForces round 150, division 2, I solved a whopping 1 problem. Why? I made the wrong choice of diving at problem D rather than trying to solve problems B and C, which were considerably easier. Well, oh well. In 151 division 2, I solved A, B, and D, and timed out on problem C. I went back and coded C more intelligently this morning, and alas &mdash; it works! I often know when naive algorithms are the right approach &mdash; I just need to pick the appropriate level of naivety in my solution :). I've decided to keep a TIL file where I slowly acquir...
ever be eligible for, and I've decided to give it my all! I've committed to practicing a little bit

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79.
By farmersrice, history, 3 years ago, In English
Hacking problems on codeforces It seems there are a significant number of hacks on Codeforces &mdash; and not the type where halyavin nukes your solution. Just recently there were those 2 chinese guys who got accounts hacked ([here](https://codeforces.com/blog/entry/61474)). Roughly a year before that there was this one round where a bunch of well-known reds had their submissions hacked and submitted by a horde of random accounts. And now this post ([here](https://codeforces.com/blog/entry/62588)). Are there any updates on these? How did they happen? Are the bugs fixed? I don't think I ever saw anything except "ok, we got hacked but 3 days later we got accounts back, problem solved". I'm not trying to say nothing is being done, of course, there is probably a lot of good work going on behind the scenes, but it seems nobody knows what exactly is happening.
round where a bunch of well-known reds had their submissions hacked and submitted by a horde of random

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80.
By Nickolas, 10 years ago, translation, In English
TCO11 as seen by a blogger, p.1 <p>TCO11 - is the second (and hopefully not the last) finals I've visited as a blogger. I hope that not everybody here followed <a href="http://community.topcoder.com/tco11/blog/">the official blog</a>, and thus my story of this trip will be read as an original art work :-) <br /><br /> </p><h3>Day -1. Arrival</h3> <br /> I arrived one day earlier than most of the finalists, on Friday evening local time. How does one do this? Long story short, you just don't rely on Barbara's choice, and (when filling travel info) write something like &quot;I like this flight, and I'm in SWISS mileage program, and I absolutely love Z&uuml;rich&quot;. Disclaimer: if everybody uses this hack, it might stop working, so beware. <br /><br />[cut] The flight to Florida was short (well, short compared to the flight to Las Vegas) and nice (a lot of movies to see and ice-cream). But most of my joy dissolved into nothing in Miami airport, when I didn't find the promised taxi. In the end my drive to the hotel ...
working, so beware. [cut] The flight to Florida was short (well, short compared

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81.
By Alex_KPR, 10 years ago, translation, In English
Duck tales — the Second Song about the Finals <p><em>Translated by Maria Belova </em></p> <p>I continue the narration about the ACM-ICPC 2011 finals.</p> <p></p> <table align="center" border="0" cellpadding="0" cellspacing="0" width="100%"> <tbody><tr> <td nowrap="nowrap" width="0%"><img src="http://codeforces.ru/renderer/7c5837c1e1d68cdbf764a6719fbe37e33fd7047c.png" height="240" width="320"></td> <td nowrap="nowrap" width="10">&nbsp;</td> <td><p>At last we got to the championship's opening :). A classic breakfast slowly but surely transferred into Bill Poucher's speech. Besides inviting his numerous colleagues to the microphone to say a couple of words, he made all the teams, volunteers and organizers stand up for greetings. In other words, he was having fun in every possible way. </p> <p>Soon all the participants were gathered by the Plaza International Hall where the contest's trial rounds and the main round were held. Yes, remarkable as it is, there were as much as two trial tests! ;) </p> <p...
and the main round were held. Yes, remarkable as it is, there were as much as two trial tests! ;)

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82.
By vexorian, 11 years ago, In English
Just lost rating for this lame bug. <blockquote>So sad, I would have solved C in round 8 since I noticed how to make my memo solution work in time (by making it forcefully consume the first element that is still in the bitmask) but... So what I did was that when I encode the used pairs, I use (x,N) for a "pair" that is just a single element, that's what generated the mistake:<br></blockquote><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; int x = mem2[mask]/100;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; int y = mem2[mask]%100;<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if(y!=N) {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cout&lt;&lt; "0 "&lt;&lt;(x+1)&lt;&lt;" "&lt;&lt;(y+1)&lt;&lt;" ";<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; } else {<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cout&lt;&lt; "0 "&lt;&lt;(x+1)&lt;&lt...
So sad, I would have solved C in round 8 since I noticed how to make my memo solution

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83.
By samiemad, history, 5 years ago, In English
THIS IS VERY UNFAIR!!! Today I participated in [contest:669], I managed to solve the first three problems in a very good time. I started with problem D. didn't take long to figure out the idea (I like it very much BTW :). I submitted and got TLE on pretest 11. I knew it was because of huge input so I added ~~~~~ ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); ~~~~~ I know that with these three lines cin/cout becomes almost as fast as scanf/printf. so I resubmitted the problem and got **pretests passed**. I have about 40 minutes left so I move to the last problem. So the system test finishes, and I am shocked that my solution for D got **TLE** on test 29!!! Although it runs in O(n) complexity!!! After five long hours of waiting till I can submit again -_- ... I just changed cin/cout to printf/scanf and get **ACCEPTED**! problem link: [problem:669D] TL submission: [submission:17493329] AC submission: [submission:17500406] I don't think there is another _unwanted_ solution...
:) I am wondering if anyone else ever had the same problem? this time or in anotherround?? I

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