Codeforces Global Round 5 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/> Hey! On [contest_time:1237] we will host [contest:1237]. It is the fifth round of a new series of [Codeforces Global Rounds](https://codeforces.com/blog/entry/65002) supported by XTX Markets. The rounds are open for everybody, the rating will be updated for everybody. The round will last for 2 hours 30 minutes, 8 problems are waiting for you, and one of them will be proposed in two versions. Scoring distribution: **500 &mdash; 750 &mdash; (750 + 750) &mdash; 2000 &mdash; 2500 &mdash; 3000 &mdash; 3750 &mdash; 4000** The prizes for this round: - 30 best participants get a t-shirt. - 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive. The prizes for the 6-round series in 2019: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The fi...

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Codeforces Global Round 9 <img src="/predownloaded/2e/e2/2ee2f0f95f05aae6ca6f47812dae2dc2aabf277b.png" style="width:200px; float:right; margin: 0 1em 1em 1em"/> Hi! On [contest_time:1375] we will host [contest:1375]. It is the third round of a 2020 series of [Codeforces Global Rounds](/blog/entry/65002). The rounds are open and rated for everybody. The prizes for this round: - 30 best participants get a t-shirt. - 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive. The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the table. - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Thanks to XTX, which in 2020 supported the global rounds initiative! The problems of this round were prepared by a team of authors: [user:adamant,2020-07-01], [user:anto...

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Codeforces Round #300 (with prizes!) Hello, Codeforces! [On Sunday, April 26th at 19:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=26&month=4&year=2015&hour=19&min=0&sec=0&p1=166) the 300'th regular Codeforces Round will take place. I would like to congratulate all Codeforces members and administration on this remarkable milestone. The platform has grown hugely in size and quality since its foundation, has hosted lots of exciting competitions, and has been providing the opportunity to everyone to hone their problem solving and algorithmic mastery. For this we thank the Codeforces platform creator [user:MikeMirzayanov,2015-04-24] and all the Codeforces crew. Keep up the incredible job, guys! That being said, I'm excited to announce that the problems on the jubilee three-hundredth Codeforces Round will be set by me, Mikhail Tikhomirov ([user:Endagorion,2015-04-24]). You may remember the past rounds with my problems: [#99](http://codeforces.com/contests/138,139), [#109](http://codeforces.com/contest...

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Good Bye 2022, Hello 2023! <img src="/predownloaded/cf/40/cf40c72e68b2aee5005a91f39e1d3404d917617b.jpg" style="float:right; margin:0 1em 1em 1em;"/> Hello, Codeforces! The year 2022 is finally coming to an end. Let's be clear. It's been a terrible year. Tomorrow I will make a wish, and you can easily guess which one. I am writing these lines, and in a few minutes the Good Bye 2022 round will begin. And this inspires optimism and even pride in the community. Despite all these difficulties and troubles, we make rounds together and participate in them. Let's be grateful. And for this, let's say symbolic thanks to 2022 and a lot assistants: coordinators, problem writers, testers, participants and sponsors. We are many and we are together. Can I have a little more detail on the Codeforces team? Let me separately say thanks and words of admiration for the work of the coordinator of coordinators [user:KAN,2022-12-30] and the senior developer [user:geranazavr555,2022-12-30]. Both of you bring a lot to Cod...

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Codeforces Round #461 (Div. 2) _Hello, Codeforces! Haven't seen ya for a while :D_ Codeforces Round #461 will take place [on Wednesday, 20:15 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23461+%28Div.+2%29&iso=20180207T2015&p1=352&ah=2). Note that the round is scheduled a bit later than usual. The round will be **rated** for all division 2 participants. Division 1 is heartly welcome aswell :) My gratitude to Kolya ([user:KAN, 2018-02-04]) for round coordination, Grisha ([user:gritukan, 2018-02-04]), Oleg ([user:x3n, 2018-02-04]), AmirReza ([user:Arpa, 2018-02-04]) and Senya ([user:senek_k, 2018-02-04]) for testing and Mike ([user:MikeMirzayanov, 2018-01-01]) for awesome Codeforces and Polygon. A special thanks goes to Dima ([user:mitterr1999, 2018-02-04]) and Camille ([user:pseuda, 2018-02-04]) for sharing a problem sketch with me. The main character of this round will be **Imp** the playful monster. Yet the statements are guaranteed to be short :) ![ ](https://vk...

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Nebius Welcome Round (Div. 1 + Div. 2, rated, t-shirts!) Hello, Codeforces! [user:Zlobober,2023-03-09] and I are glad to invite you to compete in Nebius Welcome Round (Div. 1 + Div. 2) that will start on [contest_time:1804]. The round will be rated for everyone and will feature 8 problems that you will have 2 hours to solve. I feel really thrilled and excited about this round as this is the first time I put so much effort in a Codeforces contest since I quit being a round coordinator in December 2016 (wow, that was so long ago)! We conduct this round to have some fun and we also hope to find some great candidates to join Nebius team. Solving 5+ problems in our round will be a good result and will count as one of the coding interviews. Apart from that top 25 contestants and 25 random contestants placed 26-200 will receive a branded Nebius t-shirt! <img style="float: right; margin: 0 1em 0.5em 1em; width: 400px;" src="/predownloaded/40/37/403770e78d9c8962d0bc0c20a9e1c45d0e3c5df9.png"> Some information about Nebius. I have join...

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Codeforces Round #842 (Div.2) Hi Codeforces! ================== [user:Igorfardoc,2020-01-05], [user:Vladithur,2020-02-09], [user:alexdat2000,2019-08-18], [user:gluchie,2021-03-10], [user:DeMen100ns,2020-09-19], [user:Spyofgame,2021-10-03] and me (spelling "thanh-chau-n-s-2") are delighted to invite you to participate in [Codeforces Round #842 (Div. 2)](https://codeforces.com/contests/1768). **This round will be rated for all participants with a rating lower than 2100.** - Start time: [contest_time:1768] - Duration: **120 minutes**. - Number of tasks: **6**. <img align="right" src="https://media.discordapp.net/attachments/961567157622276126/1056248841348841594/received_3472327789705304.webp?width=541&height=676" width="30%" height="40%"> <spoiler summary="This contest is brought to you by"> - <a href = "https://www.facebook.com/HocvienPTIT">PTIT</a>, my university. - <a href = "https://discord.gg/codemely">Code Mely</a>, a Vietnamese fanpage for Computer Science. </spoiler> Special thanks to: ...

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Codeforces: Results of 2018 Hi Codeforces! February 2019 is already on the calendar, which means that I was late with the report for 2018. Better late than never! Let's remember last year. In 2018, [user:_kun_,2019-02-05], [user:300iq,2019-02-05] and [user:arsijo,2019-02-05] joined the team of coordinators. The work of the coordinators is headed (and is the coordinator of the coordinators) [user:KAN,2019-02-05]. I really hope that a more measured schedule of preparing rounds by a large team of coordinators will give a better insight into the contests. The main innovations in the platform are implemented by me and the developers [user:kuviman,2019-02-05], [user:fcspartakm,2019-02-05], [user:MaximShipko,2019-02-05]. Great work on the organization of events and prizes mailing was done by [user:gKseni,2019-02-05]. Special thanks to the writers of the problems and testers. It is your content that charges the community with life and unites all of us. Thank you for the problems! And now let's summarize...

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Educational Codeforces Round 40 [Rated for Div. 2] Hello Codeforces!  On [March 22, 9:05 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=22&month=3&year=2018&hour=9&min=5&sec=0&p1=166) Educational Codeforces Round 40 will start. This will be a special round, branded by VTB and the Hello India x Russia Pro...

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Educational Codeforces Round 90 [Rated for Div. 2] Hello Codeforces! On [contest_time:1373] [contest:1373] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2020-06-24] Glazov, Adilbek [user:adedalic,2020-06-24] Dalabaev, Vladimir [user:vovuh,2020-06-24] Petrov, Ivan [us...

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Editorial of Codeforces Round #752 Thanks for participating in my contest <a href="https://emoji.gg/emoji/8771_blobheart"><img src="https://emoji.gg/assets/emoji/8771_blobheart.png" width="16px" height="16px" alt="blobheart"></a>. I hope you liked the problems. I would love to hear your feedback in the comments. If you find anything wrong in the editorial which is more likely to happen because I have written a rather long editorial to make you understand the solutions better, then comment below. Also, don't forget to upvote to pay for the editorial. See you in my next contest! [tutorial:1604A] <spoiler summary="Code"> ~~~~~ #include<bits/stdc++.h> using namespace std; int main() { int t; cin >> t; while (t--) { int n; cin >> n; int ans = 0; for (int i = 1; i <= n; i++) { int k; cin >> k; ans = max(ans, k - i); } cout << ans << '\n'; } return 0; } ~~~~~ </spoiler> [tutorial:1604B] <spoiler summary="Code"> ~~~~~ #include<bits/stdc++.h> ...

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Avito Code Challenge 2018 Hi! I'm glad to invite you to take part in [contest:981] which starts on [contest_time:981]. Any participant can join the round and it will be rated for each participant. Hope to see you among the participants! Problems are prepared by me — Ildar Gainullin. This round is conducted on the initiative and support of [Avito](https://www.avito.ru/). Avito.ru is a Russian classified advertisements website with sections devoted to general good for sale, jobs, real estate, personals, cars for sale, and services. Avito.ru is the most popular classifieds site in Russia and is the third biggest classifieds site in the world after Craigslist and the Chinese website 58.com. Many thanks to Vladislav [user:winger,2018-05-24] Isenbaev, Grigory [user:gritukan,2018-05-24] Reznikov, Ivan [user:isaf27,2018-05-24] Safonov，Alexander [user:AlexFetisov,2018-05-24] Fetisov and Shiqing [user:cyand1317,2018-05-24] Lyu for the round testing, Nikolay [user:KAN,2018-05-24] Kalinin for helping me to...

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Educational Codeforces Round 163 [Rated for Div. 2] <img alt="Neapolis University Pafos" src="/predownloaded/9a/33/9a332fadbb47050ba9405057df022a6e37eaf5c0.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/> Hello Codeforces! We are pleased to announce a new long-term partnership between Codeforces and [Neapolis University Pafos](https://www.nup.ac.cy/). Now educational rounds will be supported by Neapolis University Pafos. Stay tuned and you will find out more soon. On [contest_time:1948] [contest:1948] will start. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user...

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Codeforces Round 865 Happy Easter, Codeforces! <span style="color: white">Sadly the round will not be Easter themed :(</span> We ([user:arvindf232,2023-04-07], [user:culver0412,2023-04-07], [user:dbsic211,2023-04-07], [user:happy.potato,2023-04-07], [user:jerryliuhkg,2023-04-07]) are delighted to invite you to participate in [contest:1815] and [contest:1816], which will take place on [contest_time:1815]. Participants with a rating lower than 1900 will participate in Division 2, while participants with a rating of at least 1900 will participate in Division 1. **Notice the unusual starting time.** All the problems were authored and prepared by [user:arvindf232,2023-04-07], [user:culver0412,2023-04-07], [user:dbsic211,2023-04-07] and [user:happy.potato,2023-04-07]. Huge thanks to the following people, without whom the round would not be possible: - [user:Artyom123,2023-04-07] for excellent coordination and translation of statements. - [user:KAN,2023-04-07] for help with round preparation. - [user:j...

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XOR Hashing [TUTORIAL] This is a well known technique, but I couldn't find almost any detailed tutorial, so I'll try to help with this one. ####Motivational Problem: You have an array $A$ and $Q$ queries, which are, say if the subarray from $l$ to $r$, ($A[l]$, $A[l+1]$, $...$, $A[r]$) forms a permutation. ####Some basic observations: Only the set of elements matters, the order is irrelevant. You want to know if each element is exactly once. ####Solution: Assign a random number $randval[i]$ to each number $i$, now we can say that if the XOR of the subarray ( $randval[A[l]]$ xor $randval[A[l+1]]$ xor $...$ xor $randval[A[r]]$ ) is equal to the xor of any permutation of size $r - l + 1$ (for example $1$, $2$, $3$, ... ,$r-l+1$, which hash is $randval[1]$ xor $randval[2]$ xor $...$ xor $randval[r-l+1]$ ) the subarray is a permutation. ####Some Insights: With the XOR we have some issues, we are counting if the number of occurrences of each element is even or odd, not the real number o...

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Problems that I authored so far Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs [by](https://codeforces.com/blog/entry/108940) [user:adamant,2023-02-20] and [by](https://codeforces.com/blog/entry/108595) [user:tibinyte,2023-02-20]; I finally decided to do it after my Universal Cup contest. This is not a super-comprehensive list, I also set some problems for some local contests, but that's most of it. I want to encourage other setters to write such blogs. For me, it's very interesting to read about the backstories of some problems and also to see all the problems by some author gathered in one place (as most authors give problems to several platforms). One important point. As you will see from the comments, many of my problems were improved by other people, and I myself improved some problems by other people. I think that it's crucial to have someone to discuss your problems with (apart from the coordinator). So, here we go. | # | Date | Problem | Contest | Comment ...

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Educational Codeforces Round 96 [Rated for Div. 2] Hello Codeforces! On [contest_time:1430] [contest:1430] will start. **Note that the start time is unusual**. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user:adedalic,2020-10-10] Dalabaev, Alex [user:fcspartakm,2020-10-10] Frolov an...

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What if tourist goes rainboy mode? (Simulation) DISCLAIMER: NO TOURISTS AND RAINBOYS WERE PINGED Ah yes, two names that most people on Codeforces have heard -- <b>t<span style="color:red;">ourist</span></b> and <b><span style="color:purple;">rainboy</span></b>, one known as the CP Legend, and one as the user who does everything reverse. Such a great idea to put them together &mdash; a hypothetical user with the same ability as <b>t<span style="color:red;">ourist</span></b>, and solves problems the <b><span style="color:purple;">rainboy</span></b> way. _For those unaware of the "rainboy way", it means solving the problems in reverse order. In particular, if he cannot solve the final problem, he solves no problems in the contest._ Unfortunately, <b><span style="color:purple;">rainboy</span></b> had not yet reached red, peaking at 2398 rating. How far can this user go? We shall simulate this user through all the contests that tourist and rainboy took part in comparably, which adds up to 60 contests from [contest:745] to [cont...

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Educational Codeforces Round 85 [Rated for Div. 2] Hello Codeforces! On [contest_time:1334] [contest:1334] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2020-04-09] Glazov, Adilbek [user:adedalic,2020-04-09] Dalabaev, Vladimir [user:vovuh,2020-04-09] Petrov, Ivan [us...

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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....

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Educational Codeforces Round 111 [Rated for Div. 2] Hello Codeforces! On [contest_time:1550] [contest:1550] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user:adedalic,2021-07-13] Dalabaev, Vladimir [user:vovuh,2021-07-13] Petrov, Ivan [user:BledDest,2021-07-13] Androsov, Mak...

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Paying for College with Codeforces  ### Do You Want to Go to College? Are You Good At Writing Codeforces Rounds? If so, then read on ahead! You will learn how quick and easy it is to go to college with the help of Codeforces! <br/> <br/> ### College is Expensive. The cost of MIT, a prestigious American university, is 53,790 USD per year. Even though scholarship is usually available, the average American student ends college with 37,000 USD in student debt! [[Source](https://www.cnbc.com/2017/07/13/heres-how-much-it-costs-to-go-to-college-in-the-us-compared-to-other-countries.html)] Student loan is also very pricey, with the average loan charging 5.8% interest per year. [[Source](https://www.nerdwallet.com/article/loans/student-loans/student-loan-interest-rates)] However, Codeforces pays its problem setters big money! For a combined, Div 1+2 round, you can earn an average of approximately 400 USD. [[Source...

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Educational Codeforces Round 108 Editorial [problem:1519A] Idea: [user:adedalic,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519A] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (r, b, d) = readLine()!!.split(' ').map { it.toInt() } println(if (minOf(r, b) * (d + 1).toLong() >= maxOf(r, b)) "YES" else "NO") } } ~~~~~ </spoiler> [problem:1519B] Idea: [user:adedalic,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519B] </spoiler> <spoiler summary="Solution (adedalic)"> ~~~~~ fun main() { repeat(readLine()!!.toInt()) { val (n, m, k) = readLine()!!.split(' ').map { it.toInt() } println(if (n * m - 1 == k) "YES" else "NO") } } ~~~~~ </spoiler> [problem:1519C] Idea: [user:BledDest,2021-04-30] <spoiler summary="Tutorial"> [tutorial:1519C] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ #include <bits/stdc++.h> #define forn(i, n) for (int i = 0;...

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Codeforces Beta Round #40 Mini-Tutorial <div>I wrote this post to help my friend , Iman Movahhedi , complete <a href="http://www.codeforces.com/blog/entry/1492">this one</a>.</div><div>Round #40 was my first contest here in Codeforces and I feel I fell in love with CF just after that.<br><hr style="font-weight: bold; "></div><b>A-Translation: </b>(<a href="http://pastebin.com/YmxXqAAS">C# code</a>)<div>Many languages have built-in reverse() function for strings. we can reverse one of the strings and check if it's equal to the other one , or we can check it manually. I prefer the second.[cut]</div><div><hr></div><div><b>B-Martian Dollar:&nbsp;</b>(<a href="http://pastebin.com/EP3KPzUf">C# code</a>)</div><div>Since number of days is very small ($2 \times 10^3$) we can just iterate over all possibilities of buy-day and sell-day. This will take $\theta (n^2)$ time which is&nbsp;OK.</div><div><hr></div><div><b>C-Email Address: </b>(<a href="http://pastebin.com/mfbkckEU">C++ code</a>)</div><div>The first letter of the input string...

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Educational Codeforces Round 157 Editorial [problem:1895A] Idea: [user:BledDest,2023-11-04] <spoiler summary="Tutorial"> [tutorial:1895A] </spoiler> <spoiler summary="Solution (awoo)"> ~~~~~ for _ in range(int(input())): x, y, k = map(int, input().split()) if y < x: print(x) else: print(y + max(0, y - x - k)) ~~~~~ </spoiler> [problem:1895B] Idea: [user:fcspartakm,2023-11-04] <spoiler summary="Tutorial"> [tutorial:1895B] </spoiler> <spoiler summary="Solution (fcspartakm)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int n; vector<int> a; inline void read() { cin >> n; a.clear(); for (int i = 0; i < 2 * n; i++) { int x; cin >> x; a.pb(x); } } inline void solve() { sort(all(a)); vector<pair<int, int> > pts; for (int i = 0; i < n; i++) { pts.pb(mp(a[i], a[i + n])); } int ans = 0; for (int i = 1; i < n; i++) { ans += abs(pts[i].ft - pts[i - 1].ft) + abs(pts[i].sc - pt...

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ICPC world finals vs Codeforces rounds Codeforces rounds are shorter than the ICPC world finals (40-50% the time of ICPC contests). Yet, the ICPC world finals is not equivalent to 2 Codeforces rounds. It wouldn’t have 2 As, 2 Bs, and so on. So, an ICPC contestant will need a relatively different level of stamina than the one needed in Codeforces rounds. It seems that people who practice only over Codeforces rounds, don’t usually enjoy the same level of comfort and confidence dealing with ICPC format. There is a difference between the style of problems presented in Codeforces round, and the problems presented in ICPC world finals, and it seems that problems that fit the style of ICPC world finals are not accepted by Codeforces coordinators to be in codeforces rounds at least according to my own experience when I tried to propose a contest. Problems presented in Codeforces rounds typically have the following characteristics: - Almost no knowledge required. It has to be 100% problem solving without the need to know an...

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Educational Codeforces Round 73 Editorial [problem:1221A] Idea: [user:Roms,2019-09-20] <spoiler summary="Tutorial"> [tutorial:1221A] </spoiler> <spoiler summary="Solution (Roms)"> ~~~~~ for t in range(int(input())): n = input() l = filter(lambda x : x <= 2048, map(int, input().split()) ) print('YES' if sum(l) >= 2048 else 'NO') ~~~~~ </spoiler> [problem:1221B] Idea: [user:BledDest,2019-09-20] <spoiler summary="Tutorial"> [tutorial:1221B] </spoiler> <spoiler summary="Solution (PikMike)"> ~~~~~ n = int(input()) for i in range(n): print(''.join(['W' if (i + j) % 2 == 0 else 'B' for j in range(n)])) ~~~~~ </spoiler> [problem:1221C] Idea: [user:Roms,2019-09-20] <spoiler summary="Tutorial"> [tutorial:1221C] </spoiler> <spoiler summary="Solution 1 (BledDest)"> ~~~~~ t = int(input()) for i in range(t): c, m, x = map(int, input().split()) d = max(c, m) - min(c, m) x += d if(c > m): c -= d else: m -= d ans = min(c, m, x) c -= ans m -= ans x...

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Codeforces Round #304 (Div.2) editorial A. Soldier and Bananas ---------------------- We can easily calculate the sum of money that we need to buy all the bananas that we want, let's name it x. If n >  = x the answer is 0, because we don't need to borrow anything. Otherwise the answer is x - n. B. Soldier and Badges --------------------- Let's count the number of badges with coolness factor 1, 2 and so on. Then, let's look at the number of badges with value equal to 1. If it's greater than 1, we have to increase a value of every of them except for one. Then, we look at number of badges with value 2, 3 and so on up to 2n - 2 (because maximum value of badge which we can achieve is 2n - 1). It is easy to see that this is the correct solution. We can implement it in O(n), but solutions that work in complexity O(n^2) also passed. C. Soldier and Cards -------------------- It's easy to count who wins and after how many "fights", but it's harder to say, that game won't end. How to do it? Firstly le...

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Codeforces round #716 editorial ### [problem:1514A] If any element is not a perfect square, the answer is yes. Otherwise, the answer is no, because $a^2*b^2*...=(a*b*...)^2$. Code link: https://pastebin.com/s83sFt3G ### [problem:1514B] Let's start with an array where every single bit in every single element is $1$. It clearly doesn't have bitwise-and equal to $0$, so for each bit, we need to turn it off (make it $0$) in at least one of the elements. However, we can't turn it off in more than one element, since the sum would then decrease for no reason. So for every bit, we should choose exactly one element and turn it off there. Since there are $k$ bits and $n$ elements, the answer is just $n^k$. Code link: https://pastebin.com/0D8yL5WW ### [problem:1514C] So first observe that the subsequence can't contain any element that **isn't** coprime with $n$. Why? Because then its product won't be coprime with $n$, so when you take it modulo $n$, it can't be $1$. In mathier words, $gcd(prod \space mod \s...

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Educational Codeforces Round 102 [Rated for Div. 2] Hello Codeforces! On [contest_time:1473] [contest:1473] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2021-01-13] Glazov, Adilbek [user:adedalic,2021-01-13] Dalabaev, Vladimir [user:vovuh,2021-01-13] Petrov, Ivan [us...

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Educational Codeforces Round 60 [Rated for Div. 2] Hello Codeforces! On [contest_time:1117] [contest:1117] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extented ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2019-02-17] Glazov, Adilbek [user:adedalic,2019-02-17] Dalabaev, Vladimir [user:Vovuh,2019-02-17] Petrov, Ivan [user:B...

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CodeCraft-21 and Codeforces Round #711 (Div. 2) Editorial [problem:1498A] ================== #### [**Video Editorial**](https://www.youtube.com/watch?v=lV5cb8wh3sE) **Author and Problemsetting:** [user:ninja_28,2021-03-29] **Editorialist:** [user:sigma_g,2021-03-29] <spoiler summary="Hint"> Can you think of the simplest properties that relate a number and its sum of digits? </spoiler> <spoiler summary="Hint 2"> Note that if $X$ is a multiple of 3, then **both** $X$ as well as the sum of digits of $X$ are a multiple of 3! Can you put this property to use here? </spoiler> <spoiler summary="Hint 3"> If $X$ is a multiple of 3, then $\texttt{gcd-sum}(X) \ge 3$. Therefore, we are guaranteed that at least every third number will satisfy the constraints required by our problem $(\texttt{gcd-sum}(X) > 1)$. </spoiler> <spoiler summary="Solution"> Therefore, for the input $n$, we can simply check which one of $n$, $n+1$, and $n+2$ has its gcd-sum $> 1$, and print the lowest of them. </spoiler> <spoi...

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List of All Open Cup Contests Open Cup has very high quality problems. I made a list for all the contests containing the standings, sources, upsolving links, statements and discuss blog in codeforces. Some materials and links of old opencup contests are missing, maybe [user:snarknews,2020-11-10] could help to fill these entries. I will update the list when new opencup stages published. Note: most of the upsolving links need the logins for yandex.contest or opentrains. ## XXI Open Cup named after E.V. Pankratiev | # | Contest | Upsolving | Materials | |:--:|:------------|:--:|:--:| | Stage 1 | [Grand Prix of Eurasia](https://official.contest.yandex.ru/opencupXXI/contest/20063/standings)<br/> [XXI All-Siberian Programming Contest. Online](https://olympic.nsu.ru/files/inet_res_2020_0.pdf) | [baekjoon](https://www.acmicpc.net/category/detail/2403)<br/> [yandex](http://official.contest.yandex.ru/opencupXXI/contest/20063) | [statement](https://yadi.sk/i/dsRvTxbgJ9fDXw) [discuss](https://codeforces.com/blog/...

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Educational Codeforces Round 19 Hello Codeforces! On [April 15, 17:35 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Educational+Codeforces+Round+19&iso=20170415T1735&p1=166) will be held Educational Codeforces Round 19. This Educational Round is held as Harbour.Space university initiative. It's the second round supported by Harbour.Space. You can read the details about the cooperation between Harbour.Space and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. <div style="text-align:center"><img src ="http://codeforces.com/predownloaded/b5/00/b500f462d444675afcbf458ed4d396607277b544.png" /></div> Some educational programs in Harbour.Space are interesting for most Codeforces users. One of them is Data Science Program. Here is few words from Sergey Nikolenko, Harbour.Space lecturer and Senior Researcher, Steklov Institute of Mathematics at St. Petersburg Russia. <iframe width="560" height="315" src="https://www.youtube.com/embed/A2hw_b_PLzk" frameborder="...

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List of All Petrozavodsk Contests Like my last blog [List of All Open Cup Contests](https://codeforces.com/blog/entry/84466). I made this list for all contests from Petrozavodsk Training Camp, containing the standings, upsolving links and statements. The upsolving links of Petrozavodsk Summer 2020 are private, yandex.contest logins are needed. I will update the link if other sources found. And thanks to the efforts of [Baekjoon Online Judge](https://www.acmicpc.net/), most contests from winter 2015 to winter 2020 can be solved without private logins. For some of the rest contests, opentrains logins are needed. And for some of the rest contests, I found several other sources to virtual participant using [Virtual Judge](https://vjudge.net/), [Codeforces gyms](https://codeforces.com/gyms) and [Programmers club of PetrSU](http://acm.petrsu.ru/). For some of the rest contests, I could not find any public sources and maybe someone could help with it (I believe problems in Warsaw U Contests are from old POI or PA). ...

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Educational Codeforces Round 164 [Rated for Div. 2] <img alt="Neapolis University Pafos" src="/predownloaded/9a/33/9a332fadbb47050ba9405057df022a6e37eaf5c0.png" style="float:right;height: 200px; margin: 10px; max-width:40%;"/> Hello Codeforces! The series of Educational Rounds continues thanks to the support of the [Neapolis University Pafos](https://www.nup.ac.cy/). On [contest_time:1954] [contest:1954] will start. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user:adedalic,2024-04-11] Dalabaev, Ivan [user:BledDest,2024-04-11] Androsov, Maksim [user:Neon,2024-04-11] Mescheryakov, Rom...

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Codeforces Round #660 Editorial [problem:1388A] Idea: [user:Denisov,2020-07-30] <spoiler summary="Tutorial"> [tutorial:1388A] </spoiler> <spoiler summary="Solution (Karavaev1101)"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main(){ ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); int q; cin >> q; while(q--){ int n; cin >> n; if(n <= 30){ cout << "NO" << endl; } else{ cout << "YES" << endl; if(n == 36 || n == 40 || n == 44){ cout << 6 << ' ' << 10 << ' ' << 15 << ' ' << n - 31 << endl; } else{ cout << 6 << ' ' << 10 << ' ' << 14 << ' ' << n - 30 << endl; } } } } ~~~~~ </spoiler> [problem:1388B] Idea: [user:Karavaev1101,2020-07-30] <spoiler summary="Tutorial"> [tutorial:1388B] </spoiler> <spoiler summary="Solution (Karavaev1101)"> ~~~~~ #include <bit...

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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...

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My winning theory in IOI 2018 & 2019 — Why I won 2 golds in IOI Dear Codeforces community.<br /> According to [IOI 2019 Results](http://stats.ioinformatics.org/results/2019), I got the 25th place and got successful gold medals twice in a row.<br /> Although it was pretty close to the gold-medal border (only 6.14pts / 600 difference) and it was lower performance than IOI 2018, which I participated when I was orange in Codeforces, I had many chances to get more points in this IOI, even for top 10. Since there are not so many people who have got two gold medals in IOI (and there were many requests like "I want [user:E869120,2019-08-14] to talk about how to get gold in IOI" like [this comment](https://codeforces.com/blog/entry/66909?#comment-510127) and [this comment](https://codeforces.com/blog/entry/66909?#comment-513129)). I want to write something about IOI, which may be useful for people who will participate in IOI next year and also some years later.<br /> <br /> <br /> ### A. First of all At...

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Tutorial CodeForces Round 289 (Div.2) (Second Winter Computer Camp Selection 2015) [problem:509A] In this problem one needed to implement what was written in the statement: create matrix (two-dimensional array) using given rules and find maximal value in the table. It is also possible to see that maximal element is always in bottom-right corner. Easier solution with recursion also was enough to get AC: ~~~~~ def elem(row, col): if row == 1 or col == 1: return 1 return elem(row - 1, col) + elem(row, col - 1) ~~~~~ One may see the [Pascal's triangle](http://en.wikipedia.org/wiki/Pascal%27s_triangle) in the given matrix and understand that answer is equal to $\binom{2n - 2}{ n - 1}$ Prepared by: [user:AlexDmitriev,2015-01-31] Author of editorial: [user:AlexDmitriev,2015-01-31] [problem:509B] Suppose there are two piles with number of pebbles differed by more than $k$, then there is no solution: $a_i = \sum_{c=1}^k b_{i, c} \le \sum_{c=1}^k (b_{j, c} + 1) = a_j + k $ Now let $M = \max a_i \le \min a_i + k = m + k$. ...

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Top 50 Voted Blog Posts in 2021 Hi. Here is the list of top-voted blog posts in 2021. Find something interesting for yourself? | # | Post | Votes | Author | | - | - | - | - | | 1 |<a href="/blog/entry/95106">The Ultimate Topic List (with Resources, Problems and Templates)</a> | 4383 | [user:YouKn0wWho,2022-01-02] | | 2 |<a href="/blog/entry/96333">Codeforces Round #752</a> | 3156 | [user:YouKn0wWho,2022-01-02] | | 3 |<a href="/blog/entry/87882">User activity in the profile! [new, Feb. 2021]</a> | 3055 | [user:geranazavr555,2022-01-02] | | 4 |<a href="/blog/entry/89227">Codeforces Round #712</a> | 2866 | [user:Monogon,2022-01-02] ...

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Educational Codeforces Round 76 [Rated for Div. 2] Hello Codeforces! On [contest_time:1257] [contest:1257] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2019-10-23] Glazov, Adilbek [user:adedalic,2019-10-23] Dalabaev, Vladimir [user:Vovuh,2019-10-23] Petrov, Ivan [user:Bl...

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Codeforces Round 906 Editorial [problem:1890A] idea: [user:Cocoly1990,2023-10-28] <spoiler summary="Solution"> [tutorial:1890A] </spoiler> <spoiler summary="Code"> By [user:Cocoly1990,2023-10-28] ~~~~~cpp // Time complexity O(nlogn) because of map #include <bits/stdc++.h> const int MX = 100 + 5; int main() { int t; std::cin >> t; while (t--) { int n; std::cin >> n; std::map<int ,int> occ; for (int i = 1; i <= n; ++i) { int x; std::cin >> x; occ[x]++; } if (occ.size() >= 3) puts("No"); else { if (std::abs(occ.begin()->second - occ.rbegin()->second) <= 1) { puts("Yes"); } else { puts("No"); } } } return 0; } ~~~~~ </spoiler> [problem:1890B] idea: [user:Imakf,2023-10-28] <spoiler summary="Solution"> [tutorial:1890B] </spoiler> <spoiler summary="Code"> By [user:Imakf,2023-10-28] ~~~~~cpp #include <bits/stdc++.h> bool ok(std::string s) { for ...

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Codeforces Round #645 (Div. 2) _Сoronavirus work, coronavirus school, coronavirus rest, coronavirus time spending, coronavirus contest._ <p align="center"> <img src="/predownloaded/21/49/2149d863ac14b6520c81bebd44b1d0e544b44eb2.jpg"> </p> Hello, Codeforces! [contest:1358] will start at [contest_time:1358]. This round will be **rated for the participants with rating lower than 2100**. You will have **2 hours** to solve **6 problems**. Problems of this round were prepared by Alexey [user:Alexdat2000,2020-05-19] Datskovskiy, Ilian [user:ilian04,2020-05-19] Andrianov, Vsevolod [user:Sevlll,2020-05-19] Lepeshov. We have made an effort to create interesting problems, beautiful statements and strong tests. We wish you like problems and your rating increase. We would like to express our gratitude to: - [user:MikeMirzayanov,2020-05-19] for wonderful platforms Codeforces and Polygon! - [user:300iq,2020-05-19] for excellent coordination and helpful advices! - Thanks to [user:Siberian,2020-05-19], [use...

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Codeforces Round #885 (Div.2) Editorial [problem:1848A] Idea: [user:diskoteka,2023-07-16] <spoiler summary="Tutorial"> [tutorial:1848A] </spoiler> <spoiler summary="Solution"> ~~~~~ #include <bits/stdc++.h> using namespace std; #define int long long int32_t main() { int t; cin >> t; while (t--) { int n, m, k; cin >> n >> m >> k; int x, y; cin >> x >> y; string ans = "YES\n"; for (int i = 0; i < k; ++i) { int xx, yy; cin >> xx >> yy; if ((x + y) % 2 == (xx + yy) % 2) { ans = "NO\n"; } } cout << ans; } return 0; } ~~~~~ </spoiler> [problem:1848B] Idea: [user:diskoteka,2023-07-16] <spoiler summary="Tutorial"> [tutorial:1848B] </spoiler> <spoiler summary="Solution"> ~~~~~ #include <bits/stdc++.h> using namespace std; int main() { int t; cin >> t; while (t--) { int n, k; cin >> n >> ...

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Codeforces Round #219 Statistics [contest:372] and [contest:373] statistics (with images) [cut] : <pre> <code> --------------------------------------------------------------------------------------------- | Codeforces Round #219 (Div. 1) | --------------------------------------------------------------------------------------------- | | First | Sent | Pretest | Hacked | Systest | Accepted | Attempts | Success | Severity | | | | | failed | | failed | | | % | | --------------------------------------------------------------------------------------------- | A | 00:03 | 672 | 120 | 4 | 58 | 490 | 1461 | 33.5 | 1.98 | | B | 00:09 | 411 | 15 | 1 | 28 | 367 | 466 | 78.8 | 1.11 | | C | 00:23 | 237 | 68 | 0 | 12 | 157 | 428 | 36.7 | 1.66 | | D | 00:59 | 28 | 5 | 0 | 1 | 22 ...

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Codeforces Round #560 (Div. 3) I have nothing to say this time, so meet yet another Div. 3 round :) &lt;almost-copy-pasted-part&gt; Hello! [contest:1165] will start at [contest_time:1165]. You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests &mdash; just like you will be upset if many solutions fail after the contest is over. You will be given 6 or 7 (or 8) problems and 2 hours to solve them. Note that **the penalty*...

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Educational Codeforces Round 43 [Rated for Div. 2] Hello Codeforces! On [April 30, 17:35 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=30&month=4&year=2018&hour=17&min=35&sec=0&p1=166) Educational Codeforces Round 43 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 **6 problems** and **2 hours** to solve them. The problems were prepared by Mikhail [user:PikMike,2018-04-29] Piklyaev, Roman [user:Ajosteen,2018-04-29] Glazov, Adilbek [user:adedalic,2018-04-29] Dalabaev and me. We'd like to t...

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Codeforces Marathon Round 1 — discussion The Codeforces Marathon Round 1 is over ([results comment](/blog/entry/45592?#comment-301795)). As the final solutions are being tested, I think many participants will want to share ideas and learn alternative approaches. I'll start with the ideas I tried myself, both successful and not; as I've seen in the submissions, the contestants have more ideas, but I hope they will share themselves. For each of the solutions below, the numbers in square brackets are minimum, mean and maximum score when running on 1000 tests locally. I have to note in advance that the constants and technicalities in the solutions are not considered optimal: the score just shows approximate relation between ideas and may often be improved a bit. [cut] ----- ###### **Solution 1** [`4099 4159.699 4288`]: random. Just print 5000 random bits 100 times. ###### **Solution 2** [`4160 4226.294 4365`]: last bit memorization. The last checked bit is always wrong. For example, if the answer fo...

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Codeforces Round #215 & #216 Statistics Statistics of the rounds (official participants)<br/> [contest:367]<br/> [contest:368]<br/> [contest:369] [cut]:<br/> <pre> <code> --------------------------------------------------------------------------------------------- | Codeforces Round #215 (Div. 1) | --------------------------------------------------------------------------------------------- | | First | Sent | Pretest | Hacked | Systest | Accepted | Attempts | Success | Severity | | | | | failed | | failed | | | % | | --------------------------------------------------------------------------------------------- | A | 00:05 | 639 | 42 | 0 | 2 | 595 | 1170 | 50.9 | 1.83 | | B | 00:08 | 567 | 87 | 35 | 163 | 282 | 1366 | 20.6 | 2.20 | | C | 00:13 | 413 | 73 | 61 | 23 | 256 | 770 | 33.2 | 1.59 | | D | 0...

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New Code Jam interface: a step back in usability [This post](https://groups.google.com/d/topic/google-code/9SlOptq6gIc/discussion) in Code Jam group Hi all! This year, Google has again decided to change Code Jam user interface. The new interface has already been used for Code Jam to I/O for Women and Kick Start rounds, and from what I saw, it is even worse than the last year. Let's start. [](https://i.imgur.com/sACL7ko.png) This is what I saw when I opened Code Jam main page. This year it uses even longer domain name, [codingcompetitions.withgoogle.com](https://codingcompetitions.withgoogle.com/), and some text seems to be missing. After some investigation, I found that this occurs when a browser is configured to block third-party cookies. I configure my browser this way because I don't want some companies to track me around, and for nearly all sites, this causes no issues. On some sites, blocking third-party cookies causes single sign-on to stop working, but this is understandable. Code ...

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Problems that I authored so far Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs [by](https://codeforces.com/blog/entry/108940) [user:adamant,2024-03-21], [by](https://codeforces.com/blog/entry/108595) [user:tibinyte,2024-03-21], [by](https://codeforces.com/blog/entry/113093) [user:antontrygubO_o,2024-03-21] and [by](https://codeforces.com/blog/entry/113720) [user:wuhudsm,2024-03-21]. I finally decided to do it after Codeforces Round $934$. I would like to thank [user:Non-origination,2024-03-21], [user:GoatTamer,2024-03-21] and [user:KingRayuga,2024-03-21] for discussing the problems with me. For each problem, I tried to include the some interesting stuff if I could remember. I tried to avoid using spoilers for the problems. So you can look at the comments even if you have not tried the problem. | # | Date | Problem | Difficulty | Contest | Comment |----|-----------|---------------------------------|-----...

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Educational Codeforces Round 41 [Rated for Div. 2] Hello Codeforces! On [April 04, 17:05 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=4&month=4&year=2018&hour=17&min=5&sec=0&p1=166) Educational Codeforces Round 41 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 Roman [user:Ajosteen,2018-04-03] Glazov, Adilbek [user:adedalic,2018-04-03] Dalabaev and me. We'd like to thank Mikhail [user:PikMike,2018-04-03] Piklaye...

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Educational Codeforces Round 140 [Rated for Div. 2] Hello Codeforces! On [contest_time:1767] [contest:1767] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **6 or 7 problems** and **2 hours** to solve them. The problems were invented and prepared by Adilbek [user:adedalic,2022-12-15] Dalabaev, Vladimir [user:vovuh,2022-12-15] Petrov, Ivan [user:BledDest,2022-12-15] Androsov, Mak...

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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...

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Editorial for Codeforces Round #139 **A.** You should iterate over all dices from up to down and restore answer. You can easily find number of the bottom side of the 1st dice. Using known sides of the 2nd dice you can find pair of numbets on top and bottom side of the 2nd dice. If one of them equal to number on bottom of the 1st dice, you can restore all numbers on the 2n dice. Then using this idea you can try restore numbers on the 3rd dice and so on. If you restored all numbers, you should write YES. If for some dice you cannot uniquely determine order of numbers on the top and botton sides, there will be at least 2 placing of numbers. In this case you shoyld write NO. Author is ~Ripatti,2012-09-19 . **B.** Firstly you should generate all k-bonacci numbers less than $n$. For $k \le 32$ you can do it straightforward, for bigger $k$ you can see that all $k$-bonacci numbers less $10^9$ are powers of two only (and 0). So you will have no more then 100 numbers. Then you should use greedy algo. You should substract ...

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Codeforces Round #527 (Div. 3) I'm in the middle of the session but I'm still trying to prepare Div. 3 rounds. &lt;copy-pasted-part&gt; Hello! [contest:1092] will start at [contest_time:1092]. You will be offered 6 or 7 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests &mdash; just like you will be upset if many solutions fail after the contest is over. You will be given 6 or 7 problems and 2 hours to solve them. Note that **the penalty** for th...

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ALL CodeForces Rounds Tutorial <html> <body> <br /><br /> >>>>>>>**Hi I just Say Really Sorry For Delay in UPD This Blog...!**<br /><br /><br /> <u>This is not Complete</u> , but i try to find <b>all Tutorial codeforces round</b> and posted here , thanks in advance :D <br /><br />This post will <b> <span class="Apple-style-span" style="border-collapse: collapse;color: rgb(255,0,0);font-family: verdana , arial , sans-serif;font-size: 12.0px;"> UPD</span></span></b> after each contest . <span>If anyone have or writes any editorial that's</span> <b> <span> <span class="Apple-style-span" style="border-collapse: collapse;color: rgb(255,0,0);font-family: verdana , arial , sans-serif;font-size: 12.0px;"> not in here</span></span></b> , Plz post here for ALL . <br /><br /><b>UPD </b> &nbsp;: Table1 updated : in Future!!! <br /><br /><b>UPD </b>&nbsp;: Table2 updated : CF # 118 ...to... CF # 169 added .<br /><br /> </p><hr /><br /></p> <div align="justify"> <br /><br /><b><s...

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Educational Codeforces Round 74 [Rated for Div. 2] Hello Codeforces! On [contest_time:1238] [contest:1238] will start. Series of Educational Rounds continue being held as [Harbour.Space University](https://harbour.space/) initiative! You can read the details about the cooperation between [Harbour.Space University](https://harbour.space/) and Codeforces in the <a href="http://codeforces.com/blog/entry/51208">blog post</a>. This round will be **rated for the participants with rating lower than 2100**. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally. You will be given **7 problems** and **2 hours** to solve them. The problems were invented and prepared by Roman [user:Roms,2019-10-07] Glazov, Adilbek [user:adedalic,2019-10-07] Dalabaev, Vladimir [user:Vovuh,2019-10-08] Petrov, Ivan [user:Bl...

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Codeforces Round #506 (Div. 3) &lt;copy-pasted-part&gt; Hello! [contest:1029] will start at [contest_time:1029]. You will be offered 6 or 7 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests &mdash; just like you will be upset if many solutions fail after the contest is over. You will be given 6 or 7 problems and 2 hours to solve them. Note that **the penalty** for the wrong submission in this round (and the following Div. 3 rounds) is **10 minutes*...

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A Recap of My First Year in CodeForces Hello all on Codeforces! ------------------ It’s been just over a full year since I created my Codeforces account. Since then a lot has happened on my Codeforces journey so far. With everything that’s happened I want to look back at how I got to my current point, share what I learned in the process, recap some of my best moments, and laugh at whatever I was thinking on a few of these contests, because a lot happened. The only issue is that there’s no way I’m going to detail all **60** contests I took part in 2022. Instead I’ve chosen to “award” the 9 most memorable contests, wheter it be because I did exceedingly well or self destructed in almost hilarious fashion. A few notes before I begin: No full solutions for any problems are shown in this post but there are code snippets and discussions that are spoilers for these problems. I apologize in advance. ### First Contest &mdash; [Hello 2022](https://codeforces.com/contest/1621) This was the first contest held in 2022, ...

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Codeforces Beta Round #39 <div>I invite you all to take part in the next Codeforces Round!</div><div><br>This time the problems are written by me and&nbsp;<span class="Apple-style-span" style="border-collapse: collapse; font-family: verdana, arial, sans-serif; font-size: 13px; "><a href="http://codeforces.com/profile/sdya" title="Lieutenant colonel sdya" class="rated-user user-red" style="font-family: arial; text-decoration: none !important; font-weight: bold; color: rgb(0, 0, 204); ">sdya</a></span>. Some information about us: we both are second year students of The Faculty of Mechanics and Mathematics of Kharkiv National University named after V.N. Karazin, and we are twin brothers. We began studying programming in the 10th form, about 2.5 years ago. We do not have any significant achievements in programming competitions yet, but we hope we still have time to get some <span style="COLOR: rgb(0,95,255); FONT-WEIGHT: bold">:)</span></div><div><font class="Apple-style-span" color="#005FFF"><b><br></b>...

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Lexington Informatics Tournament 2023 **Final update**: The contest has finished! This year, since it was prepared using Polygon, it is available for upsolving in the [Codeforces gym](https://codeforces.com/gym/104511). Thanks everyone for participating! And congratulations to the top teams: | Place | Team | Points | Penalty | | ----- | ---- | ------ | ------- | | 1 | [user:Golovanov399,2023-08-09], [user:andreysergunin,2023-08-09], [user:amethyst0,2023-08-09] | 850 | 177:51 | | 2 | [user:hyforces,2023-08-09], [user:lunchbox,2023-08-09], [user:oursaco,2023-08-09] | 850 | 179:52 | | 3 | [user:GusterGoose27,2023-08-09], [user:Ritwin,2023-08-09], [user:skittles1412,2023-08-09] | 830 | 171:40 | | 4 | [user:null_awe,2023-08-09], [user:PurpleCrayon,2023-08-09], [user:penguinhacker,2023-08-09] | 830 | 178:43 | | 5 | [user:antontrygubO_o,2023-08-09], [user:244mhq,2023-08-09] | 800 | 169:11 | **Update update**: Both the [Standard Round](https://lit.lhsmathcs.org) 5-day window and CTF Round have started. GOOD LUCK HA...

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Bayan Contest Warm Up round + 50 tshirts! <img src="http://bayanbox.ir/id/2486223970916195531?view" style="width: 40%; float: right;"> - Bayan **warm-up** round will be held on Sunday, [October 5th 2014, 13:00 (UTC)](http://www.timeanddate.com/worldclock/fixedtime.html?day=5&month=10&year=2014&hour=13&min=00&sec=0) and as indicated before, it will be held on Codeforces. Warm-up round is not a required round but top 50 are going to win t-shirts and it is going to be rated for both divisions. - Problems have been prepared by [user:mruxim,2014-10-02], [user:mR.ilchi,2014-10-02], [user:havaliza,2014-10-02] . We have tried our best to make the problem-set interesting and competitive and we hope you enjoy it. - It is necessary to have a complete profile on [contest.bayan.ir](http://contest.bayan.ir/en/) before the warm-up round! And please do make sure you have selected the correct t-shirt size! - We have upgraded our contest platform, and we've made sure everything is stable, tuned and robust now. Thanks to all those ...

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Happy New Year! <div style="float:right;margin:0 0.5em 0.5em 0.5em;width:450px;"> <img src="http://assets.codeforces.com/2012/hex-calendar-2013.png" style="width:450px;"/> <center><small>Calendar: (c) 2011 Anatoly Rr</small></center> </div> The Codeforces project wishes all its users a successful New Year. May all your handles change the colors only towards red, may all your solutions go well without debugging and may you enjoy many times the coveted **Accepted** at each contest! We wish you good luck in everything you do next year &mdash; isn't that great to have luck on your side! Traditionally, the Codeforces enables the users to change their handles. Note that this is a one-time change and you won't be able to return to the previous handle. Analyze all 'for' and 'against' carefully as the handle is what you are going to be often called by the numerous participants of the Codeforces contests. We've got more good news. We've decided to increase the list of people who can get the role o...

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Yandex.Algorithm 2017, third elimination round Hi! It is my pleasure to inform you that today, [on June 4 at 15:00 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Round%203&iso=20170604T1200&ah=1&am=40) the third and final elimination round of the Yandex.Algorithm 2017 championship will take place. I'm equally pleased to tell that the problems of the round were prepared by me, Mikhail Tikhomirov. I worked for Yandex for three years, and had a great time in a friendly and professional team. Cheers to Yandex! This round wouldn't take place if not for the work of these great people: - Lidia [user:lperovskaya,2017-06-04] Perovskaya and her team who are responsible for the [Yandex.Contest](https://contest.yandex.ru/) system, - Maxim [user:Zlobober,2017-06-04] Akhmedov, previously a vigilant Codeforces coordinator, and currently a vigilant Yandex.Algorithm coordinator, - Mike [user:MikeMirzayanov,2017-06-04] Mirzayanov and the Codeforces crew who support the [Polygon](https://polygon.codeforces.com/) problem...

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Codeforces Global Rounds 2020: Final Results In 2020, with the support of XTX Markets, 6 rounds of the Codeforces Global Rounds were held. Each round was common for both divisions. All such rounds were rated for all participants. At each such round, 50 brand T-shirts were handed out, and we gave T-shirts to all problem writers! I say a big thank you to XTX Markets (and personally to Yuri Bedny and Alexander Gerko) for supporting Global Rounds. Without your help, we could not host them! I sincerely admire companies like these who come to support and develop the community that some of their employees come from. It will be great if other companies follow the example and also offer their help. We need it! The prizes for the 6-round series in 2020: - In each round, top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get...

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Codeforces Round #262 — #264 Statistics (Brief) Brief stats for rounds<br/> [contest:460]<br/> [contest:461]<br/> [contest:462]<br/> [contest:463] [cut] : ## Codeforces Round #262 (Div. 2) #### First accepted: **A** (00:01) [user:Birjik,2014-08-19] [user:E.K.Goharshady,2014-08-19] [user:Mihai22e,2014-08-19] [user:Slyusar,2014-08-19] [user:VladaMG98,2014-08-19] [user:add1ctus,2014-08-19] [user:dcms2,2014-08-19] [user:linjek,2014-08-19] <br/> **B** (00:07) [user:linjek,2014-08-19] [user:wao.uchiha,2014-08-19] <br/> **C** (00:11) [user:GFW_sb,2014-08-19] <br/> **D** (01:03) [user:quanbuwolaifuze,2014-08-19] <br/> **E** (01:34) [user:jellygendut,2014-08-19] <br/> #### Total hack attempts: +598:-274 #### Top-5 hackers: **1000** [user:Honour_00,2014-08-19] +10:-0 <br/> **1000** [user:VladaMG98,2014-08-19] +11:-2 <br/> **850** [user:linjek,2014-08-19] +10:-3 <br/> **800** [user:KingTon,2014-08-19] +8:-0 <br/> **800** [user:pk.,2014-08-19] +8:-0 <br/> ![ ](https://lh4.googleusercontent.com/-7WamkVz2llM/VAtzu1nF...

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Problemsetting Goal Since goals are very important in any individual's life, I decided to **set** a goal for myself. The target is to **set** 100 problems until I quit cp. Current progress: **40** | # | Date | <center>Problem</center> | <center>Contest</center> | <center>Difficulty</center> | Comments | Feedback | |----|---------------|----------------------------------------------------------------------------------------------|-----------------------------------------------------------------|-----------------------------------------------...

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Problems that I authored so far UPD after one year! Only a periodic summary. It will be updated continuously. I'll be glad if someone gets inspired/gives feedback :) | # | Date | Problem | Contest | Comment | | -------- | -------- | -------- | -------- | -------- | | 1 | Aug 2022 | [Ring Game](https://www.codechef.com/problems/RING_GAME) |[Codechef Starters 53](https://www.codechef.com/START53) | One of the simplest | | 2 | Aug 2022 | [Rocket Pack](https://www.codechef.com/problems/ROCKET_PACK) | [Codechef Starters 53](https://www.codechef.com/START53) | | | 3 | Sep 2022 | [Energetic Node](https://www.codechef.com/problems/ENODE_HARD) | [Codechef Starters 56](https://www.codechef.com/START56) | | | 4 | Oct 2022 | [Collinear Points](https://www.codechef.com/problems/COLLINEAR) | [Codechef Starters 59](https://www.codechef.com/START59) | Highly recommend :)| | 5 | Oct 2022 | [Maximun Sum](https://www.codechef.com/problems/MAXIMUM_SUM) | [Codechef Starters 60](https://www.codechef.com/...

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Hack me! (Codeforces Round #281 (Div. 2)) <s>While waiting for [API](http://codeforces.com/api/contest.hacks?contestId=494) to update,</s> (it has been updated already) let's look at hacks in [contest:493]. That was really good round (even I had some hacks :)). Previous posts can be found [here](http://codeforces.com/search?query=hackme). [cut] <h3>Stats</h3> Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:493A] </small> | 18 (22.50%) | 20 (25.00%)| 42 (52.50%) | 80 | 249 (13.16%) | 1643 (86.84%) | 1892 | <small> [problem:493B] </small> | 456 (62.81%) | 178 (24.52%)| 92 (12.67%) | 726 | 509 (29.84%) | 1197 (70.16%) | 1706 | <small> [problem:493C] </small> | 161 (47.35%) | 100 (29.41%)| 79 (23.24%) | 340 | 715 (58.56%) | 506 (41.44%) | 1221 | <small> [problem:493D] </small> | 22 (59.46%...

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Codeforces Global Rounds 2019: Final Results In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds were held. Each round was common for both divisions and had 7–9 problems. The duration of the rounds was 2-3 hours, depending on the number and complexity of the problems. All such rounds were rated for all participants. At each such round, 50 brand T-shirts were handed out, and we gave T-shirts to all authors and problem testers as well. The prizes for the 6-round series in 2019: - In each round, top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Final results: [cut]<br/> | Place | Contestant | = | Round 1 | Round 2| Round 3 | Round 4 | Round 5 | Round 6 | | - | - | - | - | - | - | - | - | - | | 1 | [user:tourist,2019-12-17] | <b> 2987 </b> | ...

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My cheating incident on today's contest (round #381 DIV 2) I’m going to share with you my story in today’s contest. After the system test and getting my A B C problems accepted, I was surprised of being removed from the standings board and having my problems skipped. Thanks to Mike Mirzayanov, I knew that there was a cheating incident on my profile, as my solution for problem A was identical to pashka921’s. - My solution: [http://codeforces.com/contest/740/submission/22428028](http://codeforces.com/contest/740/submission/22428028) (19:39:33) - Solution of pashka921: [http://codeforces.com/contest/740/submission/22428017](http://codeforces.com/contest/740/submission/22428017) (19:39:28) The 2 solutions are completely IDENTICAL and There is no probability that this situation happened by coincidence. FYI, his submission was before mine by 5 seconds exactly. **First, I’m going to prove that pashka921 is cheating:** 1. At every page of submission on his profile ([http://codeforces.com/submissions/pashka921](http://codeforces.com/submi...

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square869120Contest #6 in AtCoder! Hello, Codeforces!<br /> <br /> Finally, the season of square869120Contest comes. I am filled with deep emotion when I think of the dawn of this contest :)<br /> <br /> On [April 14th, 20:00 JST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20190414T2000&p1=248), an innovative contest, [square869120Contest #6](https://atcoder.jp/contests/s8pc-6) will be held. As usual, I'll invite everyone includes non-Japanese participants, and in previous contest, 20 non-Japanese participants joined in the contest. Hope in this year, much more will join :)<br /> <br /> square869120Contest is a competition which is held by a twins: [user:E869120,2019-04-09] and [user:square1001,2019-04-09]. This round is our sixth voluntary contest, counting from from our first round when we were 7-th grader. Now we are 11-th grader, but we are making much efforts to achieve continuous-growing of the contest, including some experience of writing problems of AtCoder Beginner Contests and others.<br /...

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Survey on Competitive Programming Hello! I would like to conduct a survey about competitive programming in general, including when you started, how you practice and more. There are ten questions, and it should not take more than three minutes to finish it. You can click [this link](https://docs.google.com/forms/d/e/1FAIpQLSeBHPIyQZrG7a3NZfwXNpdvjNerE31Fs9l9AXJ6t94PMhB-8g/viewform?usp=sf_link) to complete the survey. Thanks for helping! **Update 1:** One of the questions, "How confident are you on being a red coder?" now allows decimals (from 1.0 to 5.0) as responses! Also you can submit more than once now. **Update 2:** A new question is added: "Which category do you belong to on Codeforces?" (sorry for not adding it previously) **Update 3:** The survey will be accepting responses until [Thursday, October 22, 2020 at 00:55 (UTC)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Deadline+of+Survey+Responses&iso=20201022T0055). Results will be out in a few days. **Update 4:** The survey is n...

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Meta Hacker Cup Finals Meta Hacker Cup Finals ================== Good morning! The Meta Hacker Cup Finals are coming up in a few weeks, and will be held on December 10th. The contest will be 4 hours long, starting at [6:30 AM, PST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Meta+Hacker+Cup+Finals&iso=20221210T0630&p1=234&ah=4), with a streamed scoreboard reveal at [11:00 AM, 30 minutes after the contest ends](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20221210T11&am=40). In the first ever Meta Hacker Cup Finals, the top 25 programmers of the over 16,000 entrants who competed in the first 4 rounds will battle it out on the hardest problem set of the season for a $20,000 grand prize. Contestants will have 4 hours to solve as many of programming challenges as they can of the 5 to 8 algorithmic tasks which will be revealed when the contest starts. The scoreboard reveal will be streamed to the the [Hacker Cup Facebook page](https://www.facebook.com/hackercup/), with commentar...

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LOVE BABBAR and ANUJ BHAIYA Exposed!!! Lets first give the introduction of these two **DUMBOS**. **BABBAR:** Runs a YouTube channel having 300K+ subscribers **ANUJ BHAIYA:** Runs a YouTube channel having 170k+ subs. **Who am I?** _Ans_: I am also among one of the YouTubers who belong to the company Amazon. **Why am I writing this post?** _Ans_: I am wanting to clear the misconception that they have spread about the company, and how they are misusing there wrong doings to wrongly influence people to do wrong tasks. **Background**: Recently Babbar posted that he will be resigning Amazon. Next Anuj posts that Amazon asked him to choose YouTube or Amazon, and he makes a video that he left Amazon for students. The moment Anuj released the video, Babbar felt he will loose out on fame, so within an hour, he posted on Linkedin that he also stood with 3L students over Amazon. The screenshots of these things are below..  ![ ]...

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Hack me! (Codeforces Round #284 (Div. 2)) And statistics from [contest:499] (this round should be named after [user:dreamoon,2014-12-24]). Previous posts can be found [here](http://codeforces.com/search?query=hackme), including [post for div. 1](/blog/entry/15413). [cut] <h3>Stats</h3> We had only 21 successful hacks for this round (pretests were pretty good). Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other* | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>|<small>Hackers efficiency**</small>| :---:|:---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:499A] </small> | 13 (18.06%) | 39 (54.17%)| 20 (27.78%) | 72 | 108 (5.03%) | 2041 (94.97%) | 2149 | 10.74% <small> [problem:499B] </small> | 2 (2.47%) | 15 (18.52%)| 64 (79.01%) | 81 | 3 (0.14%) | 2118 (99.86%) | 2121 | 40.00% <small> [problem:499C] </small> | 6 (11.54%) | 40 (76.92%)| 6 (11.54%) | 52 | 156 (20.29%) | 613 (79.71%) | 769...

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Problems that I authored so far Since competitive programming is dying, and I'm almost retired, so it's time to review the problems I authored. Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs, [by](https://codeforces.com/blog/entry/113093) [user:antontrygubO_o,2023-02-25], [by](https://codeforces.com/blog/entry/108940) [user:adamant,2023-02-25] and [by](https://codeforces.com/blog/entry/108595) [user:tibinyte,2023-02-25]. This is not a super-comprehensive list. I set many shit problems that I don't want to share for some local contests. It can be long, and I'm not sure if I have finished half of them yet. The number of asterisks after the label indicates the recommendation levels. One asterisk means this problem is worth reading. Two asterisks mean this problem is one of my favorite problems, Three asterisks mean this problem is one of my best problems. | # | Date | Problem | Contest | Comment | | ---- | ----------- | --------------------------------------------...

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Div.1 Round Registrants & Participants Consider the following Div. 1 rounds:<br/><br/> [contest:403]<br/> [contest:406]<br/> [contest:407]<br/> <pre> Registrants Participants #236: 1011 616 (61%) #238: 1052 608 (58%) #239: 774 538 (70%) </pre> At least, **30%** of registered users didn't participate in the rounds.<br/> Do you wonder, what they really do? Do they read the problem statements or not?<br/><br/> [cut] <br/> #### Intro It was interesting for me, and I've analyzed the following information:<br/> - round registrants list <br/> - last visit time of each round registrant during round (polling interval was **5 minutes**)<br/> - official participants list <br/> In other words, ~1000 http-requests were made each 5 minutes.<br/> Dear Codeforces, I beg your pardon, if it was to much :) <br/> **I don't plan to acquire this kind of statistics anymore**.<br/> #### Brief results <pre> round userColor registrants participants neverVisited silentlyVi...

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[GYM] The 2019 “Orz Panda” Cup Programming Contest (Online Mirror) Hello, Our training round in Xidian University, named _The 2019 “Orz Panda” Cup Programming Contest_ will start on Aug 20, 2019. There are some people who wish to participate in the round but they can not reach the campus at time. So as the contest manager I decide to mirror the round on Codeforces. The problem set is prepared by Xi Ruoyao (me, [user:loujunjie,2019-08-19]). Thanks Jing Linxiao ([user:jl0x62,2019-08-19]) and Liu Sen ([user:ls961006,2019-08-19]) for testing the round. Thanks Wei Yanming ([user:wym6912,2019-08-19]) for providing IT support for the round. And thanks [user:MikeMirzayanov,2019-08-19] for Polygon and Codeforces. The online mirror will start at [contest_time:102309], one hour after the onsite round starts. Unfortunately I can't make the mirror public now, because some participant of the onsite round has Codeforces coach rights (for example [user:wang9897,2019-08-19] and [user:qkoqhh,2019-08-19]). Most participants of the “Orz Panda” Cup ar...

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Best contest I have participated in Yesterday I saw the announcement of the contest [Code Mutants](https://codeforces.com/blog/entry/65336) on Codeforces, it said contest will take place today (19th February). I went through the announcement, it said: **"Top 3 contestants will be rewarded with 250 Laddus!! from CodeChef.Some of the top contestants will be selected for onsite round where prizes worth 10,000 INR are waiting for you!!"** I thought: "Cool! I definitely should try it, I feel inspired!" So I felt inspired and went to the CodeChef. In announcement there, I saw the following:  Hoping to get to onsite, I filled in this form! Then, the contest started. Tasks turned out to be very interesting! Even more impressive was innovative Tex formatting:  After I solved the first task, I tried to submit it and clicked **Submit**. However, it was testing too...

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Surprise Language Round #6 The contest is over; the editorial is [here](http://codeforces.com/blog/entry/4633). I've mis-estimated the complexity of the problems --- but how could I possibly guess who will arrive and finish everything in 40 minutes :-) Congratulations to the winners --- the slowest and the most relaxed of them took under an hour to solve all the problems. ----- Today's round features Roco --- a little-known esoteric language with a special approach to loops and subroutines. The programs written in it look a bit bulky, especially when compared to Befunge, but this is compensated by their relative simplicity and readability. Here is a program which calculates the sum of two given numbers: ~~~ iin [0] iin [1] add [2] [1] [0] iout [2] ac ~~~ There is little information about this language on the web --- the only two sources known to me are [the author's site](http://lodev.org/esolangs/roco/) and [Progopedia article](http://progopedia.com/language/roco/) with commented sampl...

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[Tutorial] Hacking a weak hash Hello everyone, yesterday I hacked the following submission: [submission:195599340]. It wasn't trivial for me (I found it more difficult than solving the problem itself), but it doesn't require any weird mathematical knowledge. So, if you've never hacked before, you may want to try to hack that submission by yourself. Anyway, I wanted to share the hack as a tutorial (since I have not found similar blogs on Codeforces). Here is the "solution": Solution ------------------ Let's read the submission. It calculates two hashes (stored in `val[x]`). We would like to generate a collision (= two non-isomorphic subtrees that have the same hashes). Let's notice some details: - The hash is deterministic (it doesn't rely on random variables), so it's potentially vulnerable. - The hash of small trees looks "manageable" (= it doesn't grow very fast), so it may be possible to find a collision just using small trees. So, let's start printing the hashes of small trees. Actually it doesn't...

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List of Iranian Codeforces competitors <div align="center"><img src="http://earthquake-report.com/wp-content/uploads/300px-Flag_of_Iran_in_map.svg_.png"><br></div><div align="center" style="text-align: -webkit-auto;">[cut]</div>This list is not complete (contains only people I know) and may contain errors. Please write in the comments for adding new people or fixing a typo.<br><div><br></div><div><meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8"> <title></title> <meta name="GENERATOR" content="OpenOffice.org 3.2 (Linux)"> <style type="text/css"> <!-- @page { margin: 0.79in } TD P { margin-bottom: 0in } P { margin-bottom: 0.08in } A:link { so-language: zxx } --> </style> <table width="100%" cellpadding="4" cellspacing="0"> <colgroup><col width="19*"> <col width="54*"> <col width="41*"> <col width="43*"> <col width="36*"> <col width="28*"> <col width="35*"> </colgroup><tbody><tr> <td width="7%" style="border-top: 1px solid #000000; border-bottom: 1px solid #000...

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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.  [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:...

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Codeforces Global Rounds 2021: Final Results (GR13-GR18) Tomorrow will be the first global round of this year. And we are happy to sum up the results of last season. We announce the results! We remind you that the global rounds are a joint initiative of XTX and Codeforces. We are happy to announce that they continue into the new year. We hold 6 such rounds per year. All of them are open to both divisions. At each such round, 50 brand T-shirts were handed out, and we are happy to give T-shirts to all problem authors. The prizes for the 6-round series are: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. The final standings after six rounds (sorted by total points in four best placed rounds): | Place | Contestant | = | GR 13 | GR 14 | GR 15 | GR 16 | GR 17 | GR 18| |--...

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[Tutorial] Common Mistakes in Competitive Programming and How to Avoid Them One thing is for sure. You do make mistakes. I also make miskates and that's what makes us human. But what we can surely do is &mdash; to try to minimize the errors that we make throughout our life. I have compiled some of the mistakes that I made in my early Competitive Programming phase. I also mentioned how to avoid them. Also, in most cases, I will give you a chance to find out what the bug is before I reveal the culprit as I tried to make this blog interactive. The codes that I have used in this blog have been written in C++ as it is the most used language for CP. **So, if you are new to CP, stick with me as you might don't wanna repeat the mistakes that I made when I was a beginner.** #### Mistake 1 Check out the following code: <spoiler summary="Code"> ~~~~~ #include<bits/stdc++.h> using namespace std; int main() { int a = 1000'000'000,b = 1000'000'000; long long product = a * b; cout << product << '\n'; return 0; } ~~~~~ </spoiler> The outp...

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Heavy Cheating in Educational Codeforces Round 115 !!! **I did not give today's contest today but accidently I looked at the scoreboard and found a lot of submissions for problem A, B, C , D which were much higher than usual.** <a href="https://ibb.co/FzYVxxR"><img src="https://i.ibb.co/0r9tDDH/Screenshot-2021-10-10-at-4-40-05-PM.png" alt="Screenshot-2021-10-10-at-4-40-05-PM" border="0"></a> Hence, I looked online and found that all the solutions for the first 4 problems were leaked.. HERE are the screenshots. I don't want to share the link of the website , it's just for reporting <a href="https://ibb.co/nBPYk2D"><img src="https://i.ibb.co/BGnQsDg/Screenshot-2021-10-10-at-4-29-17-PM.png" alt="Screenshot-2021-10-10-at-4-29-17-PM" border="0"></a> PROBLEM &mdash; D **Training Session Solution** <a href="https://ibb.co/kmQvk0S"><img src="https://i.ibb.co/cYDVMtr/Screenshot-2021-10-10-at-4-28-11-PM.png" alt="Screenshot-2021-10-10-at-4-28-11-PM" border="0"></a> PROBLEM &mdash; C **Delete Two Elements Solution** <a href...

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[Contest] Statement Not Found: Season 2 #### Do you think you can solve CP problems without reading the problem statements? Let's find out! On [August 28, 2022 (Sunday) 19:30-22:00 GMT+8](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Statement+Not+Found+-+Season+2&iso=20220828T1930&p1=122&ah=2&am=30), I will hold an unofficial fun contest called Statement Not Found. As you can deduce from the title, there will be no problem statements (except title and samples). Your goal is to collect as many points as possible within 2.5 hours :) Obviously, this round is **unrated**. It is somewhere between April Fools contest and a legitimate contest. The contest will be OI-style, meaning there will be no time penalty. You are allowed to use any resources online to help solve the problems. There will be **12** problems. **Scoring Distribution:** 200-400-700-700-700-800-800-900-1100-1100-1100-1500 (Total: 10000) **Please read all problems** as problem difficulty is very subjective and a 1100-point problem might b...

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Codeforces Global Rounds 2019: Current Results In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. <i>At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.</i> The prizes for the 6-round series in 2019: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after two rounds: | Place | Contestant | = | Round 1 | Round 2| | - | - | - | - | - | | 1 | [user:tourist,2019-06-01] | 1706 | 1000 | 706 | | 2 | [us...

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Screencast & Editorial of Codeforces Round 898 (Div. 4) I participated in [contest:1873] and, surprisingly, solved all problems. You can watch the solutions (please, not during the contest!): <table> <tr> <th>Problem</th> <th>Screencast</th> <th>Editorial</th> </tr> <tr> <td>[problem:1873A]</td> <td><a href="https://youtu.be/43xFpkkgX4I?t=175">02:55</a></td> <td><a href="https://youtu.be/43xFpkkgX4I?t=3280">54:40</a></td> </tr> <tr> <td>[problem:1873B]</td> <td><a href="https://youtu.be/43xFpkkgX4I?t=268">04:28</a></td> <td><a href="https://youtu.be/43xFpkkgX4I?t=3388">56:28</a></td> </tr> <tr> <td>[problem:1873C]</td> <td><a href="https://youtu.be/43xFpkkgX4I?t=400">06:40</a></td> <td><a href="https://youtu.be/43xFpkkgX4I?t=3528">58:48</a></td> </tr> <tr> <td>[problem:1873D]</td> <td><a href="https://youtu.be/43xFpkkgX4I?t=543">09:03</a></td> <td><a href="https://youtu.be/43xFpkkgX4I?t=3717">1:01:57</a></td> </tr> <tr> <td...

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2 Hours Contest vs 3 Hours Contest I have been with codeforces for a long long time. It has been always my thought that why codeforces rounds are only 2 hours (usually). The things that I am sharing right now are just my opinions. I think a CF contest's difficulty is chosen by looking at the very topmost population. Maybe like 5% of the population. They should complete or almost complete the problemset within the contest time. Well, that's fair I guess. But from the top, 50% or even maybe from the top 25% would feel that they could solve another one if there was more time. That's true for everyone else too I guess. Let's say a usual codeforces round is now 3 hours. What are the pros? Most of the contestants will get 1 extra hour to think with 1 or 2 more problems that they don't get to solve within 2 hours. Speedforces effect should be reduced at least a bit. A slow but knowledgeable contestant might end up higher on some fast contestant who used to be on top of him most of the time. Doesn't everyone want to be s...

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Round #40 (Div. 2) + Special Prizes Hello, Codeforces! We are going to host a new contest at [csacademy.com](http://csacademy.com). [Round #40](https://csacademy.com/contest/round-40/) will take place on [Wednesday, August/02/2017 15:00 (UTC)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CS+Academy+Round+%2340&iso=20170802T15&p1=1440&ah=2). This round will be a Div. 2, affecting users with a rating below **1675**. #### Special prizes This round will have 3 special prizes consisting of private coaching lessons with our contest coordinator, [user:wefgef,2017-07-31]. Each lesson will be conducted on Skype and will last for 1 hour and 30 minutes. You can find out more details on the contest page. #### Contest format: - You will have to solve **5** tasks in **2** hours. - There will be full feedback throughout the entire contest. - Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style). - Tasks will have dynamic scores. According to the n...

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Codeforces Global Rounds 2021: Current Results (GR13-GR17) In 2021 (as in 2019 and 2020), with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds are held: common rounds for both divisions of 7–9 problems each. The duration of the rounds is 2-3 hours, depending on the number and complexity of the problems. All such rounds are rated for all participants. <i>At each such round, 50 brand T-shirts are handed out, and we are happy to give T-shirts to all problem authors.</i> The prizes for the 6-round series in 2021: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the five rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after five rounds (sorted by total points in four best placed rounds): | Place | Contestant | = | GR 13 | GR 14 | GR 15 | GR 16 | GR 17| | - | - | - | - | - | - | - | - | | ...

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Codeforces Popularity Ranking Hello Codeforces! There has been several blogs similar to this. I know about [TOP 15 most popular users on codeforces](http://codeforces.com/blog/entry/49122) and [Who is the most popular?](http://codeforces.com/blog/entry/21041). But as none of these are updated, I thought this might be helpful. I have just calculated the most popular handles in Codeforces. I only considered those handles which have at least one rated contest. Begging my pardon to them who hasn't participated in any rated round. And here, the popularity depends simply on the number of people you are friend of. The complete standings can be found [here](https://docs.google.com/spreadsheets/d/1ADlF-bd6pBYCap75yzf-pUnVwI9f9YmPkiYNW3lD-xo/edit?usp=sharing)(This may took a while to load at the bottom). Anyway here is Top 200 handles. | Rank | Handle | Follower | |---|---|---| 1. | [user:tourist,2018-08-22] | 14082 | 2. | [user:Petr,2018-08-22] | 6430 | 3. | [user:OO0OOO00O0OOO0O00OOO0OO,2018-08-22] | 420...

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Educationals Rounds Link (From Starting) I saw on Codeforces on a regular basis, that there are a lot of questions and answers about practicing and practicing more. Although It is my opinion that the Educationals Rounds are best for this, at least for people like me. They learn from it and the problems are very nice and interesting. There are many Educationals Rounds will come and I will also try my best to keep this blog update. Although if you want to generate these links <s>at any time</s> locally you can find the code on my GitHub repo: https://github.com/adshin21/Codeforces-Contest-Selector-By-Div-s So I've collected the links for all the educationals rounds that has happened. <table class = "bordertable" align="center"> <tbody> <tr> <td>Educational Round 1 </td> <td> <a href= " http://codeforces.com/contest/598" >http://codeforces.com/contest/598</a></td> <tr> <tr> <td>Educational Round 2 </td> <td> <a href= " http://codeforces.com/contest/600" >http://codeforces.com/contest/600</a></td> <tr> <tr> ...

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Hack me! (Codeforces Round #278 (Div. 1)) Waiting for next round, let's take some time and look at hacks in [contest:487]. That was really good round for hackers :) Previous posts (including post for Div. 2.) can be found [here](http://codeforces.com/search?query=hackme). [cut] <h3>Stats</h3> Yeah, everyone saw that there were plenty of hacks for problem A. How many exactly? Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other* | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:487A] </small> | <strong>460 (80.70%)</strong> | 96 (16.84%)| 14 (2.46%) | 570 | 58 (11.09%) | 465 (88.91%) | 523 | <small> [problem:487B] </small> | 8 (42.11%) | 8 (42.11%)| 3 (15.79%) | 19 | 99 (27.58%) | 260 (72.42%) | 359 | <small> [problem:487C] </small> | 67 (90.54%) | 5 (6.76%)| 2 (2.70%) | 74 | 45 (28.66%) | 112 (71.34%) | 157 | <small> [problem:487D] </sm...

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Is the Problem Rating System broken...? Hello, fellow Codeforces fans! During my training I select problems by their Problem Rating. But recently I noticed something peculiar about this feature. Namely, problems that have the same ratings may actually differ in hardness! The difference in hardness cannot be, in my opinion, explained by the rounding-to-the-nearest-100 rule, as my percieved difference should be sometimes in the order of 200-250. In my opinion this is connected to the Divisions system. Suppose that I want to solve a 1900 rated problem from the Problemset. I noticed that in such situation I'm able to solve such a problem in around 15 mins if it comes from Div3, around 30 mins if it comes from Div2 and up to 50 mins for Div1 problems. Those times include implementation time. My explaination for that is that a 1900 rated problem in Div3 is either F or G, in Div2 it's D or E and in Div1 it's A or B. If most participants solve problems in the A,B,C,... order, div3 participants have to solve 5 or 6 problems ...

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Codeforces Global Rounds 2020: Current Results (GR7-GR10) In 2020 (as in 2019), with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. <i>At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all problem authors and problem testers.</i> The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after four rounds (sorted by total points in four rounds): | Place | Contestant | = | GR 7 | GR 8 | GR 9 | GR 10| |--|--|--|--|--...

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Codeforces Global Rounds 2020: Current Results (GR7-GR9) In 2020 (as in 2019), with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. <i>At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all problem authors and problem testers.</i> The prizes for the 6-round series in 2020: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after three rounds (sorted by total points in three rounds): | Place | Contestant | = | GR 7 | GR 8 | GR 9| |--|--|--|--|--|--| ...

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All Div3's Links This is for boosting the speed and have good commonds with the tricky implementations There are many Div. 3 will come and I will also try my best to keep this blog update. Although if you want to generate these links at any time locally you can find the code on my GitHub repo: https://github.com/adshin21/Codeforces-Contest-Selector-By-Div-s So I've collected the links for all the Div. 3's that has happened. <table class = "bordertable"> <tbody> <tr> <td> Div3 Round 1 </td> <td> <a href=http://codeforces.com/contest/977>http://codeforces.com/contest/977</a></td> </tr> <tr> <td> Div3 Round 2 </td> <td> <a href=http://codeforces.com/contest/978>http://codeforces.com/contest/978</a></td> </tr> <tr> <td> Div3 Round 3 </td> <td> <a href=http://codeforces.com/contest/988>http://codeforces.com/contest/988</a></td> </tr> <tr> <td> Div3 Round 4 </td> <td> <a href=http://codeforces.com/contest/999>http://codeforces.com/contest/999</a></td> </tr> <tr> <td> Div3 Round 5 </td> <t...

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Codeforces Global Rounds 2019: Current Results After Five Rounds In 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. <i>At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.</i> The prizes for the 6-round series in 2019: - In each round top-100 participants get points according to the [table](https://pastebin.com/QT5sXEaT). - The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest. - The best 20 participants over all series get sweatshirts and place certificates. Current standings after five rounds: | Place | Contestant | = | Round 1 | Round 2| Round 3 | Round 4 | Round 5 | | - | - | - | - | - | - | - | - | | 1 | [user:tourist,201...

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Hacks became useless? DISCLAIMER: sorry for my poor english, hope you can understand this text :) Hello! Firstly: Codeforces is a beautiful platform, sure. In my mind hacks became useless. Why? Ok, see: Many easy problems (D1AB/D2ABCD) are "multitest" problems. It is really hard to hack them, because pretests are very strong. But what if I want to hack some hard problems? Hm, i tried to hack some hard problems, but in div2 rooms are very small, and i discovered that there were only 2-3 people who solved some hard problems. Anyway, i saw that [user:MiFaFaOvO,2020-04-16] in one of his screencasts was very annoyed about it too. But if i will try to hack D2B for example, i would find roughly 10 people, and the chance of succes hack is very small, so it is useless to spend time on it. So, it is really hard to hack someone, and we can see that the quantity of hacks is very small in some previous rounds! - What is my solution? Ok, lets make rooms bigger from 40 to 80. Wha...

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Being destroyed by today's Div2 Contest Hello, Codeforces community! Today's contest was a nightmare for me. Let me tell you what happened. First of all, I was 2 minutes late due to the networking issue. When I start the contest, 1000+ contestants already solved A. This made me extremely stressed. I eventually calmed down, and passed both A and B in 15 minutes. The next problem is C, which looks very trivial. However, I did not expect that I got stuck and could not figure out the solution in 20 minutes! So I had no choice but to go and look at other problems. My English is not that good. So I chose problem E, the one with the shortest problem statement. I found it unbelievably easy and solved it in just 10~15 minutes. Now I still have 75 minutes left. I looked at D. Very easy, I can just use some STL (std::map and std::set) and binary search to solve it. However, it might took me a while (like 20~30 minutes?). I looked at F. Seems not so difficult as well. By the time, around 2000 contestant...

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Codeforces Contest Rules This is a detailed and formal version of the Codeforces contest rules. If you just want to learn the rules, we recommend that you first read the post [Codeforces Contests](http://codeforces.com/blog/entry/456). The organizers may slightly modify the rules for specific rounds, then this information is contained in the announcement of the round. The following rules should be regarded as default rules. ### General information about a round 1. You need to register to participate in a round. The registration opens six hours before the start of the contest and closes 5 minutes before it, unless the information about the round states otherwise. 1. The system of conducting contests has two interface languages available: Russian and English. The contestants can switch between these two languages. 1. A round continues for 2 hours, unless the information about the round states other duration time. 1. Contestants are given 5 problems to solve, unless the information about the ...

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Codeforces Round #256 & #257 Statistics (Brief) [contest:448], [contest:449] and [contest:450] brief round statistics [cut] : [contest:448]:<br/> ### #256 (Div. 2) #### First accepted: **A** (00:02) [user:Bubbler,2014-07-16] [user:Misaka_916852,2014-07-16] [user:Shark,2014-07-16] [user:TAT,2014-07-16] [user:ZuoWeiYiGeZhangZhe,2014-07-16] [user:alan.amanov,2014-07-16] [user:himanshujaju,2014-07-16] [user:iSlava,2014-07-16] [user:mirceadino,2014-07-16] [user:rureggaeton,2014-07-16] [user:sea5,2014-07-16] <br/> **B** (00:09) [user:alan.amanov,2014-07-16] [user:felix,2014-07-16] <br/> **C** (00:12) [user:wwt10086,2014-07-16] <br/> **D** (00:06) [user:sillyhook03,2014-07-16] <br/> **E** (00:40) [user:sillyhook03,2014-07-16] <br/> #### Total hack attempts: +53:-137 #### Top-8 hackers: **350** [user:yash.15296,2014-07-16] +4:-1 <br/> **300** [user:TAT,2014-07-16] +3:-0 <br/> **250** [user:chenrui9551,2014-07-16] +3:-1 <br/> **200** [user:himanshujaju,2014-07-16] +2:-0 <br/> **200** [user:Empress,2014-07-16] +2:-0 <b...

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Every Problem I've Ever Set As some of you might already know, this blog is inspired by my very good friend [user:tibinyte,2023-06-07]'s post, which you can find [here](https://codeforces.com/blog/entry/108595). The golden problems are my personal favourites, the green problems are pretty good and the red problems are not worth your time in my opinion. Problem difficulty legend: - <span class="rated-user user-blue">1600</span><i>?</i> : the rating shown is just my estimate, and most likely innacurate - <span class="rated-user user-orange">2100</span><i>*</i> : the rating shown is the average of all the votes cast on the editorial regarding the difficulty of the problem - <span class="rated-user user-red">2500</span><i></i> : the problem has this exact rating on codeforces Infoleague problems ------------------ <table class="bordertable"> <thead> <tr> <th><center>#</center></th> <th><center>Date</center></th> <th><center>Problem</center></th> <th><center>Contest</center></th> <th><center>Dif...

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Notes on Codeforces Beta Round #112, Div2- A, B, C, D, E [problem:165A] Straightforward implementation with exhaustive enumeration. [problem:165B] The main idea is binary search, since if $v$ is a reasonable result, then any $v'>v$ also serves as a reasonable answer. Moreover, we can calculate $k^p$ in previous, and it is sufficient to consider $p$ up to $40$, since the problem guarantees that the maximum value of $n$ is $10^9$. Do not worry that $k^p$ will lead to overflow, as we will never use the value which exceeds $v$. The left work is to adopt binary search to find the minimum value of $v$. [problem:165C] We can solve this problem based on two cases. 1) $k=0$: we find out all the consecutive intervals $[l, r]$ that only 0s are included. This interval contributes $\frac{t(t+1)}{2}$ to the final answer, where $t=r-l+1$. 2) $k>0$: we find out each interval $[l, r]$ that exactly $k$ 1s are included and integers with indices $l$ and $r$ are also 1s. Then, we move from position $l$ to the left and find out the first inde...

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Solutions to Codeforces Beta Round #40, A, B(prefix idea), C, D, E(Turan's theorem) A. Translation This is a simple problem. If the two strings have different length, then the answer must be "NO"; otherwise, we just reverse one of the strings and compare whether they are exactly the same or not. B. Martian Dollar A straightforward solution is to first enumerate the days when to sell, and for the i-th day, enumerate all days from the first one to the i-th one and find out the j-th day when one can buy with the cheapest price, where 1=<j<=i. Then, the money will be b%a[j]+b/a[j]*a[i], where "x/y" means "integer division". Finally, we output the maximum value as the answer. This solution has complexity O(N^2). However, we can further reduce it to O(N). The idea is to build another array p[N], where p[i] denotes the minimum value of a[0],a[1],...,a[i]. p[0] is initialized as p[0]=a[0], while p[i] can be computed as p[i]=min(a[i],p[i-1]), which takes O(N) complexity. Thus, if we sell on the i-th day, the money will be b%a[i]+b/p[i]*a[i], and the maximum one is jus...

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Hack me! (CF Round #262) Hey, I wanted to start new series about hacking. I think that this part of programming contests is really underrated, but can be helpful for both people solving problems (you should know what tricky cases you need to consider) and people writing problems (you should know how to write nice tests covering everything). So in this series, which I will try to continue, I will talk over hacks at Codeforces Rounds. I will try to do some statistics and take a look at most common mistakes in passing contests. It is my first article related to hacking (and first at all :)), so feel free to suggest something, correct me on some errors or mistakes (my English still can be much better :)) and tell about your hacks. Thanks in advance! So let's move to [contest:460]. **Update:** added country wise statistics (at the end). **Update:** added chart with hacks over time and first hacks. **Update:** the handles are now full of colours, with many thanks to awesome [user:sylap97,2014-08-2...

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Hack me! (Codeforces Round #282 (Div. 2)) Quite delayed, but here we have stats about hacks in [contest:495]. Previous posts can be found [here](http://codeforces.com/search?query=hackme), including [div1](http://codeforces.com/blog/entry/15151). [cut] <h3>Stats</h3> Problem | <small>Successful hacks</small> | <small>Unsuccessful hacks</small> | Other | Sum | <small>Solutions which can be hacked</small> | <small>Accepted solutions</small> | <small> All solutions on final tests</small>| :---:|:---:|:---:|:---:|:---:|:---:| <small> [problem:495A] </small> | 623 (85.58%) | 76 (10.44%)| 29 (3.98%) | 728 | 47 (2.65%) | 1727 (97.35%) | 1774 | <small> [problem:495B] </small> | 274 (79.42%) | 60 (17.39%)| 11 (3.19%) | 345 | 232 (27.17%) | 622 (72.83%) | 854 | <small> [problem:495C] </small> | 103 (56.59%) | 75 (41.21%)| 4 (2.20%) | 182 | 426 (64.06%) | 239 (35.94%) | 665 | <small> [problem:495D] </small> | 0 | 0 | 0 | 0 | 3 (27.27%) | 8 (72.73%)| 11 | <small> [problem:495E] </small> | 0 | 0 | 0 | 0 | 0 | 0 | 0 | <ce...

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FIICode Contest 2022 Hello CodeForces! I would like to announce the 7th edition of FIICode – a contest organized by the Faculty of Computer Science Iași. This year, the contest will be held on CSAcademy and will consist of two rounds, on the 14th and 15th of May. Each round will have 5-6 problems of various difficulties – something like a CF Div 2. The final ranking will be computed by summing up the scores in each of the two rounds. There will be 7 Romanian and Moldavian winners (read [here](https://fiicode.asii.ro/algoritmica) about prizes), but also the top 5 international competitors will receive T-shirts and other goodies! The problems are prepared by [user:cristian1997,2022-04-15], [user:Gheal,2022-04-15], [user:lungualex00,2022-04-15], [user:Fanurie,2022-04-15], [user:a_dumi,2022-04-15], [user:vmnechita,2022-04-15], [user:Brodicico,2022-04-15], [user:RazvanPanaite,2022-04-15], [user:IulianOleniuc,2022-04-15], [user:ApetriiRadu,2022-04-15]. **To officially take part in the contest, and...

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How to be red: Arpa [user:Arpa,2021-02-28]'s interview: _-Salam AmirReza_ -Salam Natalia _-Do you remember becoming red?_ -Yes, exactly one year ago, for the first time, I touched red just with 2405 :)) [cut] _._ _-Did you celebrate it?_ -For sure, I celebrated it in my mind for several days. But if you mean a real celebration, with others' participation and some sweet, drink and food, no. I was in my hometown at that time, and my little brother and my parents became happy. _-Was becoming red the most special for you, or getting some other color was more emotional?_ -I remember when I reached Candidate Master. I was 15 at that time. Note that at that time, purple was starting from 1700. That was very nice. But for sure, becoming red was much more emotional. _-What color was your goal when you started?_ -I rarely had a goal. Becoming red became my goal in 2019. Especially, I never imagined that I could sometime reach IGM. I exactly remember the contest Globa...

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Screencast – Codeforces Round #653 (Div 3) + Interesting detailed timestamps Hi everyone :) You could notice that last time I trying hard to make content on my youtube channel better. If you don't know anything about my channel, I do video analysis of nice educational Competitive Programming problems, observe cool algorithms, do screencasts, also I plan to add coding interview problems content. I truly believe that potentially I can help many people as well as myself to achieve not only professional goals but also become much better in CP. So, today I recorded an interesting and in some moments funny screencast with cool detailed timestamps. ~~~~~ 0:00 - Starting 0:30 - Solving problem A 3:30 - Solving problem B 6:16 - Solving problem C 10:05 - Solving problem D 14:27 - Solving problem E1 28:23 - Thinking on problem E2 41:16 - Switched to problem F 1:10:34 - Solving problem E2 1:36:37 - Debugging problem E2 1:40:00 - Finishing debugging and finally submitting E2 1:41:00 - Thinking on the last problem F ~~~~~ I hope you would...

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Invitation to CodeRed- 2018  Hello Codeforces! [Aparoksha](https://aparoksha.org/) presents to you an all-new flagship event **CodeRed** in association with ACM. If you have the appetite for algorithmic problem solving, then don't miss it out! It will be a 5-hour long **team event** with a maximum size of the team being **3 members**. The preliminary round will be held on Codechef, and the onsite round will be held during Aparoksha. The total prize money is worth **INR 50,000**. The **best 40 teams** will make it to the onsite round. Also, top **2** teams in the **online round** will get **INR 3000 and 2000** respectively, along with Codechef Laddus. All teams making it to the onsite round will get CodeRed T-shirts. Contest link is here &mdash; [CodeRed 2018](https://www.codechef.com/CODR2018) The problem set comprises **6 problems** of varying difficulty level. So be ready to have a nail-biting exper...

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Blog collection <p>________________________________________________________________________________________<br><br></p><h3><b>Puzzle</b></h3><ul><li><a href="http://codeforces.com/blog/entry/66">Red and Black hair</a>, </li><li><a href="http://codeforces.com/blog/entry/112">The 12 chairs and diamonds</a></li><li><a href="http://codeforces.com/blog/entry/228">Monty Hall Problem</a></li></ul><br><br><h3>Useful <br></h3><ul><li><a href="http://codeforces.com/blog/entry/70">Petr Mitrichev, 3 days in Sao Paulo Training Camp 2010</a></li><li><a href="http://codeforces.com/blog/entry/512">Useful links</a></li><li><a href="http://codeforces.com/blog/entry/529">Problem Set Analysis Of CodeForces</a></li><li><a href="http://codeforces.com/blog/entry/546">Discussions Of CodeForces Round</a></li><li><a href="http://codeforces.com/blog/entry/1492">ALL CodeForces rounds Tutorial</a></li><li><a href="http://codeforces.com/blog/entry/1534">Online Judge Locator</a></li><li><a href="http://codeforces.com/blog/entry/170...

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Moscow International Workshop ACM ICPC 2016 hosted by MIPT <img src="http://codeforces.com/predownloaded/60/61/60617f09640bf908bd1821839dbeb849745084f0.png" style="float:right; margin: 0 1em 1em 1em;"> The international training camp to prepare for ACM-ICPC 2016 is running on the base of Moscow Institute of Physics and Technology. [Moscow International Workshop ACM ICPC 2016](http://it-edu.mipt.ru/ru/fall_training_2016) is open educational and training student meeting for sports programming which takes part for the 7th time. The meeting has started on the 8th of November and will continue until the 18th of November. Remember that two month ago already in Codeforces [were written](http://codeforces.com/blog/entry/46962) about technical details of the camp. It consists of 9 working days in English with daily contests (the main moderator of these contests is the coordinator of Open Cup named by E.V. Pankratiev, the chief editor of Snarknews: Oleg Khristenko); tutorials, lectures, practice time and evening activities &mdash; sports, excurs...

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Kotlin Heroes: Episode 6 Results <img src="/predownloaded/82/40/82402fe8f53b090c87c1f9b0fa4ba5807294ed9f.png" style="width:300px;float:right;margin:0 1em 1em 1em;"/> Hello Codeforces! The sixth round of the Kotlin Heroes series recently finished! All the rounds are available to be used for practice here: [Episode 1](https://codeforces.com/contests/1170,1171), [Episode 2](https://codeforces.com/contests/1211,1212), [Episode 3](https://codeforces.com/contests/1297,1298), [Episode 4](https://codeforces.com/contests/1346,1347), [Episode 5: ICPC Round](https://codeforces.com/contests/1431,1432) and [Episode 6](https://codeforces.com/contests/1488,1489)). Thanks to everyone who participated – you inspire us to work even harder on the problems for the next round, and we think you’re really going to like them! Congratulations to the top three contestants: 1. [user:tourist,2021-03-22] 1. [user:Egor,2021-03-22] 1. [user:Tlatoani,2021-03-22] A Kotlin Heroes t-shirt and exclusive Kotlin stickers will be present...

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What is wrong with system tests and hacks? Hello, Codeforces! First of all, I would like to emphasize, that I am writing this post not out of fury or disappointment, but I just want to verify, if there are anyone who share my POV. Yesterday [contest:1923] was held. And I liked it! Problems were very nice and interesting. But one thing happened, that is still on my mind. My [B](https://codeforces.com/contest/1923/problem/B) got [FST](https://codeforces.com/contest/1923/submission/247902606) (Failed System Tests). For those unfamiliar with this system, I'll explain it to you. When you send your code, during round it works on some relatively small tests set, after the contest is finished your last successful submission for each problem is retested on expended tests set (it also includes all successful hacks). This system exists to lessen delays in testing queue. In my mind the problem behind this system is that during the round you see if your code failed some test, and you can find an issue and fix it, but after the end of the...

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101 Hack 39 — HackerRank I'm glad to invite you all to participate in [101 Hack 39](https://www.hackerrank.com/contests/101hack39)! The contest will start today at [16.30 UTC, July 12](https://www.timeanddate.com/worldclock/fixedtime.html?msg=101+Hack+June&iso=20160712T1630&p1=1440&ah=2). All problems are prepared by me. It will be my first HackerRank round so far. Also you may want to check my Codeforces round which held very lately [contest:671] or [contest:672]. There will be five tasks and two hours for you to solve them. Contest will be rated and top-10 contestants on the leaderboard will receive amazing HackerRank T-shirts! I want to thank [user:wanbo,2019-07-08] and [user:ErdemKirez,2019-07-08] for testing problems and for their great advices. It was awesome to work with them. I hope you will like the problemset. I tried my best to prepare interesting problems, so I strongly recommend you all to participate. Please read all of the problem statements during contest, because some problems ma...

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Codeforces Round #244 (Div. 2) Statistics [contest:427] round statistics [cut] : #### First accepted: **A** (00:01) [user:avoit,2014-05-02] [user:bssanches,2014-05-02] [user:imhereonlyforcookies,2014-05-02] [user:jsannemo,2014-05-02] [user:linjek,2014-05-02] [user:llIIIlIlII,2014-05-02] [user:md5_84,2014-05-02] [user:solonkovda,2014-05-02] [user:yourHighness,2014-05-02] <br/> **B** (00:04) [user:VeniVidiVici,2014-05-02] <br/> **C** (00:09) [user:Miras321,2014-05-02] <br/> **D** (00:40) [user:Rivx,2014-05-02] <br/> **E** (00:38) [user:1rw6,2014-05-02] <br/> #### Total hack attempts: +36:-165 #### Top-6 hackers: **400** [user:HelloFdu,2014-05-02] +4:-0 <br/> **300** [user:xiaoyingnan,2014-05-02] +3:-0 <br/> **200** [user:Rivx,2014-05-02] +2:-0 <br/> **200** [user:albertg,2014-05-02] +2:-0 <br/> **150** [user:sayhellotoanshu,2014-05-02] +2:-1 <br/> **150** [user:VeniVidiVici,2014-05-02] +2:-1 <br/> #### Other info ![ ](https://lh5.googleusercontent.com/-r74Ncmgjoe8/U2QMPsj2EoI/AAAAAAAABw0/VlE7w9mQlOQ/s0/C...

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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...

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HackerRank HourRank 2 Hello Codeforces !!! I'd like to announce the second HackerRank HourRank round! The contest will be held on [16:00UTC Monday, 2 November 2015](https://www.timeanddate.com/worldclock/fixedtime.html?msg=HourRank2+&iso=20151102T16&p1=1440&ah=1) . Contestants will be given 4 problems and 1 hour to solve them. You can sign up for the contest [here](https://www.hackerrank.com/hourrank-2). Top 10 winners will receive a HackerRank T-Shirt. The contest is rated for all users. Contest is prepared by me([user:svanidz1,2015-10-27]). I want to thank whole Hackerrank team, and especially [user:Shafaet,2015-10-27], [user:wanbo,2015-10-27] and [user:malcolm,2015-10-27] for testing the tasks. Wish you good luck. **UPD1:** Score distribution : 25-40-60-90. **UPD2:** Contest starts in less than 3 hours. **UPD3:** All problems will have partial scores, Contest starts in less than 1.5 hours. **UPD4:** Contest starts in less than 5 minutes. **UPD4:** Contest is finished. Editorials...

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Codeforces Round #345 (Div. 2)-------The Solution And Code  A. Joysticks ================== Friends are going to play console. They have two joysticks and only one charger for them. Initially first joystick is charged at a1 percent and second one is charged at a2 percent. You can connect charger to a joystick only at the beginning of each minute. In one minute joystick either discharges by 2 percent (if not connected to a charger) or charges by 1 percent (if connected to a charger). Game continues while both joysticks have a positive charge. Hence, if at the beginning of minute some joystick is charged by 1 percent, it has to be connected to a charger, otherwise the game stops. If some joystick completely discharges (its charge turns to 0), the game also stops. Determine the maximum number of minutes that game can last. It is prohibited to pause the game, i. e. at each moment both joysticks should be enabled. It is allowed for joystick to be c...

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Educational Codeforces Round 40 Editorial [tutorial:954A] [tutorial:954B] [tutorial:954C] [tutorial:954D] [tutorial:954E] [tutorial:954F] [tutorial:954G] [tutorial:954H] [tutorial:954I]

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Codeforces Beta Round #40 (Div. 2) <div>Hi, everybody!</div><div><br></div><div>Welcome to the&nbsp;&nbsp;"Codeforces Beta Round #40 (Div. 2)".&nbsp;Let the weather cloudy (at least in Saratov), and the round began with the unavailability of the server (we apologize for a fail), but I hope the tasks will bring you pleasure.</div><div><br></div><div>Wish you high ratings,</div><div>MikeMirzayanov</div>

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HackerRank World Codesprint May Hello CodeForces Community! HackerRank is back with another [World Codesprint](https://www.hackerrank.com/contests/may-world-codesprint/challenges)! Join us on 21st May, exact time [can be found here](http://www.timeanddate.com/worldclock/fixedtime.html?msg=HackerRank+World+Codesprint&iso=20160521T16&p1=%3A). Its your chance to win upto $2000 Amazon gift cards/bitcoins and tshirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.]. Contest duration is 24 hours. The contest will be rated. If two person gets same score, the person who reached the score first will be ranked higher. The challenges were prepared by [user:osmanorhan,2016-05-19], [user:muratt,2016-05-19], [user:ma5termind,2016-05-19], [user:forthright48,2016-05-19], [user:cherrytree,2016-05-19]. I would like to thank [user:wanbo,2016-05-19] and [user:malcolm,2016-05-19] for helping to prepare this round. Editorials ...

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SPC '22 Final Contest | Programming Club, IIT Madras Hola, coders! On [Monday, August 15 2022, at 17:05^UTC+5.5](https://www.timeanddate.com/worldclock/fixedtime.html?msg=SPC+%2722+Final+Contest&iso=20220815T1705&p1=553&ah=2&am=30), [Programming Club IIT Madras](http://cfi.iitm.ac.in/club/Programming%20Club) will be hosting Summer Programming Camp 2022's final contest &mdash; SPC Final Contest and we would like to invite all of you for the same. It will be a combined **unrated** round for all divisions. It is a team contest for the official participants &mdash; you can participate in a team of 2 or individually. The contest consists of 15 problems [ICPC Style Scoring] to be solved in 150 minutes, in the format of a _Speed Programming Contest_. We believe the problems will be fun and exciting to solve for you guys :D The contest is of Div.3 level but with challenging problems in the end. It will provide a good range of problems in terms of difficulty (from very easy problems to ones that can challenge experts), and e...

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Invitation to CodeRed- 2019 by IIIT Allahabad  Hello Codeforces !! **[Aparoksha](https://aparoksha.org/)** is back with the second edition of the flagship-event **CodeRed**. Last year's [CodeRed 2018](https://codeforces.com/blog/entry/57818) was a great success with over 900 teams registering for it. If you have the appetite for algorithmic problem solving, then don't miss it out! It will be a 4.5 hour long **team event** with a maximum size of the team being **3 members**. **The participants need not be from the same college/institution/organization.** The preliminary round will be held on **Codechef**, and the onsite round will be held during Aparoksha. The total prize money is worth **INR 125,000 (Including goodies for all teams selected for onsite round, travel expenses* and cash prizes worth INR 50,000)**. The **best 40 teams** will make it to the onsite round. Also, top **3** teams in the **online round*...

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Main test for problem C2 is not strong enough (For codeforces global round 5.) There are some users who submit the same code for C1 and C2, but get main test failed for C1 and passed for C2. This JavaScript code shows that there are 12 users who passed C1 and failed C2: (run this in the developer console on a Codeforces page) <spoiler summary="Code"> ```js function sleep(ms){ return new Promise(function(resolve,reject){ setTimeout(resolve,ms) }) } async function custom_test(source,programTypeId,input){ // There's no official API // adapt from CF customtest js code const data=await $.post('/data/customtest',{ csrf_token: Codeforces.getCsrfToken(), source: source, sourceCode: source, tabSize: 4, programTypeId: programTypeId, input: input, output: '', // not _tta: 510, // ? communityCode: '', action: 'submitSourceCode', }) while(true){ sleep(2500) const response=await $.post("/data/customtest", { communityCode: "", action: "getVerdict", customTestSubmit...

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Wrong Answer on CodeForces 40 Div 2 Problem D Hi guys. I'm getting Wrong Answer for Test 10 in Problem D of&nbsp; the CodeForces 40 Round. Here's my code <a href="http://ideone.com/be1hs">http://ideone.com/be1hs</a><br><br>I used a Dynamic Programming approach to solve this problem. My states here are <br>1) the current row position of my pawn<br>2) the current column position of my pawn<br>3) the remainder of the sum of all the numbers that the pawn has covered so far.<br><br>Upon termination, my recursive function will store the biggest number ( divisible by k + 1 ) that can be achieved, coming to a particular position with that particular remainder. <br><br>Regards<br>tarif

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HackerRank HourRank 4 Hello Codeforces community! I'd like to announce the fourth HackerRank HourRank round! The contest will be held [on Sunday, 3th January 2016](https://www.timeanddate.com/worldclock/fixedtime.html?msg=HourRank%204&iso=20160103T1600&ah=1&am=0). You can sign up for the contest [here](https://www.hackerrank.com/contests/hourrank-4/challenges). Top 10 winners on the leaderboard will receive a HackerRank T-Shirt. Problems have been set by Shafaet Ashraf ([user:Shafaet,2015-12-30]) and Aleksa Plavsic ([user:allllekssssa,2015-12-30]). Competitors will have 1 hour for solving 4 problems with variable scoring distribution. Contest are rated for all HackerRank users. We want to thank HackerRank team, especially to [user:wanbo,2015-12-30 ] for testing and great advices and [user:svanidz1,2015-12-30] for helping. If you have any question be free to ask. The whole HackerRank team wish you good New Year with great success both in private life and numerous programming contests! Se...

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HackerRank World Codesprint April Hello CodeForces Community! I am glad to share that HackerRank's [World Codesprint April](https://www.hackerrank.com/world-codesprint-april) is scheduled on [29-April-2016 at 16:00 UTC](http://www.timeanddate.com/worldclock/fixedtime.html?msg=World+Codesprint+April&iso=20160429T16&p1=%3A). Contest duration is 24 hours. Go ahead and [register now](https://www.hackerrank.com/worldcodesprint) to show off your coding abilities, and win upto $2000 Amazon gift cards/bitcoins and tshirts. [Note: Winners from US and India will receive Amazon Gift Cards. Winners from other countries will receive equivalent USD amount in bitcoins.] The problems were prepared by [user:malcolm,2016-04-28], [user:stonefeang,2016-04-28], [user:svanidz1,2016-01-27], [user:ma5termind,2016-04-28] and [user:shafaet,2016-04-28]. Thanks to [user:wanbo,2016-04-28] for testing the problems and [user:forthright48,2016-04-28] for helping with editorials. The contest will be rated. If two person gets same score,...

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Something about third-party code in Codeforces Round#604 Div1 For Codeforces Round604 Div1 E，it can be showed that this problem is quite similar to a problem in Chinese Contest WinterCamp 2007，the code can be easily searched by Baidu or Google. for example,the following blog posted the code in 2018 https://www.cnblogs.com/zhoushuyu/p/9146420.html here is my submission,[submission:66347301],i used the code from the blog and change the input by myself According to the rule about the Third Party code，i think i should not be unrated. [user:MikeMirzayanov,2019-12-07] Please investigate this matter，Greatly thanks PS: Mike didn't answer me for 40 hours.. It really makes me anxious..Please help me.. It is fixed now,really thanks.

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Kotlin Heroes: Episode 7 Results <img src="/predownloaded/82/40/82402fe8f53b090c87c1f9b0fa4ba5807294ed9f.png" style="width:300px;float:right;margin:0 1em 1em 1em;"/> Hello Codeforces! The second round of the Kotlin Heroes series in 2021 was a great one! Thanks to the authors and all who participated! We are very happy to see new people among the winners. All the rounds are available to be used for practice here: [Episode 1](https://codeforces.com/contests/1170), [Episode 2](https://codeforces.com/contests/1211), [Episode 3](https[user:Petr]://codeforces.com/contests/1297), [Episode 4](https://codeforces.com/contests/1346), [Episode 5: ICPC Round](https://codeforces.com/contests/1431), [Episode 6](https://codeforces.com/contests/1488) and [Episode 7](https://codeforces.com/contests/1533). The “7” from “Kotlin Heroes: Episode 7” was the lucky number for this top three contestants: 1. [user:Petr,2021-07-27] 1. [user:tourist,2021-07-27] 1. [user:Maksim1744,2021-07-27] A Kotlin Heroes t-shirt and exclusiv...

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2015 Facebook Hacker Cup Round 1 ## **General Comment** I did not spend too much time on thinking about the execution time since the 6-minute is usually much more than the required in the usual online contest (e.g., 2 seconds for CodeForces for instance). So, for each problem, I took whichever way leading me to code reliably. Also, for each problem, I did lots of stress testing since I screwed up few contests (e.g., the large input in the previous Google Code Jam) before by not fully testing my codes with respect to the full constraint given by the problem. For A and C, I generated the edge cases manually and compared the computed answers from the brute force approaches and made sure they match. For B and D, I generated the theoretical worst case to make sure they are handled properly using my codes. Thankfully, I hit few segmentation fault problems 4-5 hours into the contest, from which I tried few approaches to increase the stack size; manipulating the size limit in `#include<sys/resource.h>` did the trick ...

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HackerRank HourRank 3 Hello Codeforces :) The third round of HourRank is here and I am glad to be able to welcome you all. The contest will be held on [02:00UTC Wednesday, 2 December 2015](http://www.timeanddate.com/worldclock/fixedtime.html?msg=HackerRank+HourRank+3&iso=20151202T02&p1=1440&ah=1). You can sign up for the contest from [here](https://www.hackerrank.com/hourrank-3). The contest is rated and top 10 contestants from leaderboard will win HackerRank T-Shirts :D The contest contains four challenges that are prepared by me ([user:forthright48,2015-11-29]). I want to thank the HackerRank team and [user:Shafaet,2015-11-29], [user:wanbo,2015-11-29], [user:svanidz1,2015-11-29] and [user:Arterm,2015-11-29] for testing the tasks. Contestants will have 1 hour to solve these problems, which I hope is enough, but not more than enough. I hope you will enjoy your hour with Alex, Professor Numerico, Dumdum and Karas. Best of luck for the contest. See you on leaderboard. **UPD1:** Less than ...

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How I Stay Productive in Self-Isolation [Usual shameless self-advertisement!](https://www.youtube.com/watch?v=CFagJwWW7ys) Hey, guys! Lately I have seen a lot of my buddies' productivity graphs looking like this:  So, I've decided to share 3 tips from my life experience about how I manage to keep myself motivated, focus and productive as hell. P.S: I am a Computer Science student auto-isolated in my dorm room. We are talking about 40 m³ here. It's pretty easy for a guy like me to get nuts in a situation like this. So let's get it started: #### _**1. Put on a suit!**_ No bro, I'm not joking. It might sound stupid, but it's a game changer. As I said, I live in a dorm room, so it's really easy to get off track when your bed is literally 0.5 meters away from the table you study. The table you study on is the same one you eat on. Then I have the sink 2 meters away. This ...

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HackerRank HourRank 1 Hello Codeforces community ! I am glad to announce the first HackerRank HourRank round! The contest will be held on [15th October 2015 at 15:00 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=HourRank%201&iso=20151015T1500&ah=1&am=0). You can sign up for the contest [here](https://www.hackerrank.com/hourrank-1). Top 10 winners on the leaderboard will receive a HackerRank T-Shirt. Problems have been set by Shafaet Ashraf ([user:Shafaet,2015-10-11]) and Aleksa Plavsic ([user:allllekssssa,2015-10-11]). Competitors will have 1 hour for solving 4 problems with variable scoring distribution. Contest are rated for all HackerRank users. I want to thank whole HackerRank team for support and opportunity to organize the new format of competition. Especially I want to thank [user:Shafaet,2015-10-11], he is really great guy and his help and contributon in contest preparation are incredible. Also I want to thank [user:wanbo,2015-10-11] and [user:svanidz1,2015-10-11] for testi...

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HackerRank HourRank 5 Hi Codeforces ! I'd like to announce the fifth HackerRank HourRank round! The contest will be held on [16:30 UTC Monday, Feb 1 2016](http://www.timeanddate.com/countdown/generic?iso=20160201T2030&p0=371&msg=HourRank+5&font=cursive&csz=1). Contestants will be given 4 problems and 1 hour to solve them. You can sign up for the contest [here](https://www.hackerrank.com/hourrank-5). Top 10 winners will receive a HackerRank T-Shirt. The contest is rated for all users. HourRank 5 is prepared by me([user:svanidz1,2016-01-23]). I want to thank whole Hackerrank team, and especially [user:Shafaet,2016-01-23], [user:wanbo,2016-01-23] and [user:malcolm,2016-01-23] for testing the tasks. Wish you good luck. **UPD1:** Score distribution : 20-40-50-80. Contest starts in less than 5 hours. All problems will have partial scores. **UPD2:** Contest starts in less than 1.5 hours. **UPD3:** Contest starts in less than 15 minutes. **UPD4:** Contest is over. Editorials are published. Co...

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Codeforces Round #743 (Div.2) B — Swaps I think this problem is not very hard and it's interesting. Description: You are given $2$ arrays $a$ and $b$ and the length of them is $n$. - $1$, $3$, $5$, ......, $2 * n - 1$ is in $a$. - $2$, $4$, $6$, ......, $2 * n$ is in $b$. $\mathrm{Algorithm}\ 1:$ we use the array $mp_i$ is $i$ the distance to the $a_1$ or $b_1$. the code is: ```cpp for (int i = 1;i <= n; ++ i) cin >> a[i], mp[a[i]] = i - 1; for (int j = 1;j <= n; ++ j) cin >> b[i], mp[b[i]] = i - 1; ``` We can enumerate the $i$ and the $j$, and the answer is $mp_{a_i}\ +\ mp_{b_j}$. the code: ```cpp #include <iostream> #include <cstdio> #include <cstdlib> #include <cstring> #include <string> #include <cmath> #include <iomanip> #include <cctype> #include <vector> #include <stack> #include <queue> #include <map> #include <set> #include <algorithm> #include <utility> #include <deque> #include <ctime> #include <sstream> #include <list> #include <bitset> #include <climits> ...

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Tutorial and tips to reach Master. "As mentioned earlier, practice hard. This is the only common factor that experts have. And for whom reached expert, I'll write a sequel from expert to master soon." (From my blog, Tutorial and tips to reach Expert). That soon happened to be 1.5 years after the first blog...... First, I'm sorry for the immense delay. Many bad things happened to me, like not staying in the Master rating range, having a health problem, etc. That's why I wrote the blog this late. Introduction ------------------ This is a sequel, but I am going to write the steps to Expert from scratch since the original blog([https://codeforces.com/blog/entry/81882](https://codeforces.com/blog/entry/81882)) has poor quality. Your journey is going to be divided into 4 sections. Each section contains the knowledge you need to have, the practice you must do, the performance you need to have in a contest, etc to advance to the specific rating. Section 1. From the beginning to escaping Gray(1200) ---------------...

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Unofficial list of IZhO 2023 participants The first day of IZhO 2023 is going to be at 2nd of February. I want to make a list of participants, can you please share the Codeforces handles of participants and their country? The list is sorted by Codeforces rating, but there might be changes due to current rounds. Thank you! <table> <thead> <tr> <th> CF Rank </th> <th> CF Handle </th> <th> Country </th> </tr> </thead> <tr> <td> 1 </td> <td> [user:syrtin,2023-01-28] </td> <td> Kazakhstan</td> <tr> <td> 2 </td> <td> [user:Tekor,2023-01-28] </td> <td> Kazakhstan</td> <tr> <td> 3 </td> <td> [user:StupidGuy13,2023-01-28] </td> <td> Georgia</td> <tr> <td> 4 </td> <td> [user:drdilyor,2023-01-28] </td> <td> Uzbekistan</td> <tr> <td> 5 </td> <td> [user:erankyun,2023-01-28] </td> <td> Armenia</td> <tr> <td> 6 </td> <td> [user:Zhabka,2023-01-28] </td> <td> Kazakhstan</td> <tr> <td> 7 </td> <td> [user:amunduzbaev,2023-01-28] </td> <td> Kyrgyzstan</td> <tr> <td> 8 </td> <td> [user:kitsune...

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Coping Lozzers What the hell!! Why this people copy **Zaaaaammmmmnnn**.   The hell the solution for A,C problem of Educational Codeforces Round 118 (Rated for Div. 2) were posted on telegram group at 9:24PM(UTC+5:30) almost 40 min ago and 600+ views it has so like **Zaammmnn**. How bad the ratings suffer!!! I dont know how bad specialists and pupil's and newbie might feel. It just demotivates! **PLEASE STOP COPYING**. **PLEASE STOP COPYING**. **PLEASE STOP COPYING**. Codeforces Sponsered by telegram does it real mean?(soln) Please take some action as copying cases are found on telegram itself. The Group name itself spits the spell!!!!. **Codeforces**. **Codeforces**. **Codeforces**. PS: I love **CODEFORCES** alot But please take actions please!! **Please support**

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Progress on Coding Week 1: Extremely distressed. Only one of the 7 questions I have attempted in contests has passed all test cases. I solved all of them but there is a time complexity issue with 6 of them! Most of my solutions are pretty naive and not efficient. Hopefully, I'll get better with practice. 43 days before end of "Holidays". Week 2: Gave a div 3 contest. Solved first question in 40 minutes even though I guessed the correct algo in 2. Had to stop in the middle for some work. After the contest, solved second question in 15 minutes! Solved the third one in about 40 mins as well. Felt the questions were easy. Couldn't do 4,5,6. Couldn't submit Q2,3. Still, some progress. Week 3: Gave div 2 contest and realized I should not look div 1,2. Practicing everyday. Explored leetcode as well. Week 4: Round 647 div2. 2/6 problems solved. Attempted two more but couldn't figure out the logic. Got best rank yet at around 7.4k. First rating increase. Working on gfg and codeforces contest questions. ...

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Make Round #677 unrated Hello codeforces! This round was very cool, I won't deny that. But, many people "precomputed" answers for E. How is it possible? Let me introduce you to [OEIS](https://oeis.org/). This is an online encylopedia of series and sequences, and it's very well-known. Consider the output of sample 4 (12164510040883200). It's a pretty random number, right? No. Let's see what happens. Paste this URL: https://oeis.org/search?q=12164510040883200&language=english&go=Search We can see that the result is a sequence of integers 1, 3, 40, 1260, 72576, 6652800, 889574400, 163459296000, 39520825344000, 12164510040883200, 4644631106519040000, 2154334728240414720000, 1193170003333152768000000, 777776389315596582912000000 which turn out to be the solutions for problem E. Problem E was solved by many in a similar fashion, and it's extremely unfair to the others if people who cheated get away with it. I request you to scrap problem E, or make the round unrated. Thank you! [user:vovuh,2020-10-...

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DONT USE IDEONE WHILE OFFICIAL ROUNDS !! Today I just recived system email from codeforces that my solution is similar to some users for 1494A from last Educational round ,, in contest my compiler crushed and now I have to use any online editor, I used Ideone to test my code the default in IDEONE your code will be public to other users, this is the cheaters submission and that's not there first time. I wish the admins deal with them and again, check the privacy of your code if you will use ideone . Sorry for bad English ((:  

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Bayan — live coverage Hi everybody, it's 11:10 local time at Tehran, I'll tell you how the Bayan Programming contest 2013 (1391) onsite Finals is progressing.  **22:17**. Peter50216, cerealguy and Egor are top-three! Congratulations! **22:05**. Closing ceremony. The rejudge took place for one problem. **18:30**. Not everything of Funkoders has been judged yet, so the results of this additional fun contest will come later. **18:29**. **It's over!** **18:27**. Announcement: two minutes to the end of the contest. It should have 5 though. **18:10**. It's a fun competition, so there are two guys entertaining competitors and spectators:  **18:04**. Every couple of minutes one of the baloons exploid, making a person next to it jumping up. **17:54**. Only the first submission will count. There are 15 problems. Competitors hope that the problems are not harder than in the main round. ...

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Test generator on C++ **Hello, CodeForces!** ================== #### **Information** I wrote a test generator on C++. It is very simple, it contains 2 functions: "generate a random number between $a$ and $b$, so that this random number is a multiple of $k$" (function: `genint(a, b, k, add)`, where `add` is whether to "add" this number to the test) and "generate of a random string". There's something to be written here. - Generates a string of random length between $a$ and $b$, so that it is a multiple of $k$. - Consisting of the given characters. You can set characters in two ways: write the interval `("a-f", "x-z")` or a individual character `("m", "o")`. (function: `genstr(a, b, k, pattern, add)`, where `pattern` is an array of given intervals or individual characters). <spoiler summary="Code"> ~~~~~ #include <bits/stdc++.h> using namespace std; #define int long long string test = ""; int genint(int a, int b, int k, bool add) { if (a == b) { if (add) test += to_string(a); ...

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Submit in Sixty Seconds (russian "Сабмит за 60 секунд"). <p>I wonder what's happening with me last time.</p><p>Let me tell you my short story.</p><p>During the "Unknown language contest #1" I've spent too much time on solving relatively easy task (D). So, when I solved E it was about 40 seconds before the end of the contest. When I saw it, my eyes popped out and I was trying to find this file to submit. The only problem is that when you have no time, your hands don't obey. But I did it, in about last 30 seconds, yoohoo! And even system tests were passed.</p><p>During the "Codeforces Beta Round #58" my solution on task B was hacked. I was trying to find my mistakes, but.. there is no mistakes in my code! Then I understand, that "int" is too small to store values that I need. I've changed it to "long" and judje's verdict was "MLE". Ok, I killed one array. And now judje's verdict was "TLE" on the hacker's test.</p><p>And, SUDDENLY, I realized, that Java's Scanner is tooo slooooow (maybe, it's God's punishment for moving from C++) . I wrote new ...

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Problems that I authored so far Hi everyone! I have been inspired [by](https://codeforces.com/blog/entry/108940) [recent](https://codeforces.com/blog/entry/108595) [events](https://codeforces.com/blog/entry/113093) to write this blog post. This list is not comprehensive, but mostly because I do not keep detailed logs of problems I have written. There are a few things you will notice after reading through these problems. In no particular order: 1. Most of these problems are not "high-quality" &mdash; they would never see the light of day on a CF round for example. This is mostly due to my lack of skill in generating "high-quality" problems. You'll see that a lot of my problems are generated from observing real-life events and then constructing problems out of those scenarios. There are many ideas that have been proposed and thrown into the void because they were worse. I think there are a couple problems in this list that are actually good problems, but most of them I am not particularly proud of. 2. The diffic...

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Teams going to Gwalior/Pune Regionals **UPDATE:** I've uploaded the code that I used to generate this on Github, in case someone needs to generate something similar: [Codeforces Team Rating Calculator](https://github.com/abdullah768/Codeforces-Team-Rating-Calculator) The regional round has ended and here's the final Ranklist: https://www.codechef.com/public/rankings/ACM18GWR Inspired by the list of teams going to Kharagpur regionals, I decided to make one for Gwalior/Pune regionals. The list contains all the teams from the official Gwalior website. If you know the usernames of members of any of the teams. Please update the excel file: ### [HERE] (https://docs.google.com/spreadsheets/d/1jRvwzQzp1DOcazgI7jXBB8uY3u7Ze_eQ77Xa75_Q810/edit?usp=sharing) Team rating calculation has been done according to the official Codeforces team rating calculation formula. The table will be updated with details from the excel file every 6 hours or so. Last Updated: 10 pm, 12th December IST | No. | AIR | Team Name ...

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First Ever Users to Reach Some Rating Milestones Revised: ratings below 1500 and greatest rises Several days ago I published a [table](https://codeforces.com/blog/entry/104320) with first people to reach certain ratings. It featured only ratings above 1500, and [user:adamant,2022-07-09] advised to do the same, but on achieving ratings below 1500. I found it quite interesting, and, after several days of collecting data about participations of 447911 Codeforces users, I finally made this table. [cut] For several reasons I firstly put another table. This is the table of greatest rating rises in the history of Codeforces. The reasons are: 1. I have collected so much data from Codeforces that it would be blasphemy not to use it in as many ways as possible. 2. These tables might intersect a lot: it's easier to get a terrific rise in ratings if you are low-rated. (Many people abuse this and deliberately get very low-rated to make a great jump.) 3. Someone recently posted a table with greatest rating rises and falls. I wasn't able to find this table to check whether it was...

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Problem Topics Good Day to you! I've been asked to make some topic-wise list of problems I've solved. Even though I couldn't involve all problems, I've tried to involve at least "few" problems at each topic I thought up (I'm sorry if I forgot about something "easy"). I've alredy made such list once anyway I've tried to include more problems now &mdash; so here it is: <spoiler summary="aho"> http://www.spoj.com/problems/ADAJOBS/ URI 2226 (5) //[NICE][NUMBERS][DP] http://www.spoj.com/problems/SUB_PROB/en/ http://codeforces.com/contest/696/problem/D 8 http://www.spoj.com/problems/AHOCUR/ 5 //Aho-Corassic + DP https://www.codechef.com/problems/LYRC (5) //Sample aho-brute-force http://codeforces.com/problemset/problem/346/B //Proposed by [user:bradyawn,2019-08-03] </spoiler> <spoiler summary="automat"> 6861 [LA] //CYK UVA 10679 //Suffix Automat http://www.spoj.com/problems/STRMATCH/ //Suffix Automat &mdash; trie might do too http://www.spoj.com/problems/NSUBST...

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Knapsack the tutorial -------------------- -------------------- <a name="TOC"></a> > **Teleporter:** **[**[Previous](#status)**]** | | | **[**[Next](#statement)**]** ### <strong> <center style="color:red;"> Table of content </center> </strong> | Teleporter | Description | | :--------------------------------------------------------------- | :-------------------------------------------------------------------------------------------- | | [I. STATEMENT](#statement) | Taking about the problem | | [II. EXAMPLE](#example) | To understand the problem better | | [III. Solution for small number of element &mdash; N](#small_n) | How much will you get in each...

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Knapsack the tutorial -------------------- -------------------- <a name="TOC"></a> > **Teleporter:** **[**[Previous](#status)**]** | | | **[**[Next](#statement)**]** ### <strong> <center style="color:red;"> Table of content </center> </strong> > This blog isnt the best but worth spending time to read it | Teleporter | Description | | :--------------------------------------------------------------- | :-------------------------------------------------------------------------------------------- | | [I. STATEMENT](#statement) | Taking about the problem | | [II. EXAMPLE](#example) | To understand the problem better | | [III. Solution for small number ...

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