About div1E (round #810) I am the coordinator of Round #810. I will be brief and clear. The div1E problem was copied by one of the two authors, it was not a coincidence. For this reason, the **div1 part of the round is unrated**. Div2 stays rated. Sometimes known problems appear in a contest, it happened to me as an author and to any problem setter who has organized many contests. This is never a reason to make a round unrated. Today something different happened, the problem was deliberately copied and the author did not tell anything to anybody (not even to the other author). Codeforces (and me personally) condemns this behavior. A final personal remark: I feel sad. Please future authors: do not copy problems. It's a waste of everyone's time.

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Hello 2018 Hello 2018! If you're still thinking what to do on the eighth day of year 2018, pay attention! The first round for both divisions of the new year starts on January 8 at 17:35 Moscow time ([what about other timezones?](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Hello+2018&iso=20180108T1735&p1=3396&ah=2&am=30)). Four important components of Hello 2018 will be the same as in Good Bye 2017: - Div1 + Div2 combined - 8 problems - 2 hours 30 minutes - Rated But there will also be a substantial difference: - Different problems The problems of this round have been proposed and prepared by [user:YakutovDmitriy,2018-01-06], [user:BudAlNik,2018-01-06] and myself. Thanks to everyone without whom this round wouldn't be possible as well: [user:AlexFetisov,2018-01-06], [user:Golovanov399,2018-01-08], [user:KAN,2018-01-06], [user:MikeMirzayanov,2018-01-06], [user:PavelKunyavskiy,2018-01-06], [user:qwerty787788,2018-01-06], [user:VArtem,2018-01-07], [user:winger,20...

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Giving negative feedback to contests in comments //This is a short post motivated by the comment section of the last Div2 round (and of several rounds before) Every problemsetter tries to make his contest as good as possible, and is upset when something goes wrong. Most problemsetters don't set contests for money, the payments are not worth the time and efforts spent on coming up with problems, preparing them, and hosting the contest. The most rewarding thing in this process in not the money, it's to see contestants enjoying your problems. That's why feedback is so important. If the comment section is filled with comments praising the contest, setter will most likely want to come back with another contest, and if it's filled with hate and offenses, it's possible that setter will just give up on problemsetting and won't want to host another round. This means two things. First, if you liked the round, or some particular problem, why not to write a comment about it? I am sure that most setters would really appreciate it, a...

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Who sorry_dreamoon really is Hello everybody. So I was really bored tonight and looked at so many comments being like "[user:sorry_dreamoon,2015-02-18] is X" and then people arguing and disagreeing. Since I had nothing better to do, I decided to finally unravel the truth of who he actually is. Here is the full case and how I actually got to him, hope you enjoy! :D Selection ------------------ Let's start by the obvious. He managed to get first place in Div2 and he got second in Div1 (would've been first if the scores were static). So what we know is that he is really good. Let's look at the past 10 Div1 contests. It turns out that only 8 times it happened that someone with a rating of less than 2500 got in top5. This is 8 times out of 50 people being in top5. But he was second and almost first, so he is better than that. It turns out actually, that in the past 10 Div1 contests, only 2 times it happened that someone with rating less than 2500 got in top3. Combining this information with [user:sorr...

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Codeforces Raif Round 1 [Div. 1 + Div. 2] Привет, Codeforces! Присоединяйтесь к объединенному Div1 и Div2 раунду [contest:1428], который будет проходить при поддержке Райффайзенбанка и начнётся в [contest_time:1428]. **Он будет рейтинговым и открытым для обоих дивизионов. Обратите внимание на нестандартное время начала раунда.** Все задачи были придуманы и подготовлены [user:bensonlzl,2020-10-15], [user:oolimry,2020-10-15], [user:errorgorn,2020-10-15], [user:dvdg6566,2020-10-15], [user:shenxy13,2020-10-15]. Спасибо: - [user:isaf27,2019-05-10] и [user:KAN,2020-10-15] за коодинацию раунда и помощь в подготовке - [user:zhangguangxuan99,2020-10-15] за то, что он лучший IOI тренер <3 - Армии наших тестеров: [user:Ari,2020-10-15], [user:KAN,2020-10-15], [user:Monogon,2020-10-15], [user:Prabowo,2020-10-15], [user:SYY,2020-10-15], [user:SleepyShashwat,2020-10-15], [user:TeaTime,2020-10-15], [user:Tlatoani,2020-10-15], [user:_rs_,2020-10-15], [user:agul,2020-10-15], [user:cstuart,2020-10-15], [user:dantoh,2020-10-15],...

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

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Codeforces Round #736 Hello, Westeros! I'm glad to invite you to [contest:1548] and [contest:1549], which will be held on [contest_time:1548]. The round will be rated for both divisions. Each division will have 5-7 problems and 2 hours and 15 minutes to solve them. There **will not** be an interactive problem, so yay!!! This round would not have been possible without the following individuals: 1. [user:Aleks5d,2021-07-30], for awesome coordination of my round. 2. [user:Benq,2021-07-30], for extensive testing and contributions throughout the round, especially for [problem:1548E]. 3. [user:1-gon,2021-07-30], for discussing problems and statements with me for hours on Discord. 4. [user:amgfrthsp,2021-08-01], for translating statements into Russian. 5. [user:MikeMirzayanov,2021-08-01], for Codeforces and Polygon. #### 32 testers The round had a total of 32 testers. I tried to get a "rainbow" of testers to help guarantee a most balanced round. Thank to you to each and every one of them! - ...

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Some thoughts on recent discussions Hello everyone! I finally decided to write some response/explain my view after all recent discussions of my problems and rounds I coordinate, and I would like to make a few points. **1.** After some recent contests there were a lot of comments saying that Data structure problems should appear as easy problems (say, D2A-D2D in a Div2 of $6$ problems)    I don't think I agree with this. To begin with, I don't think that having Data Structure problem is a requirement for a good contest at all, not just in first few positions.  However, for positions D2A-D2D, I just don't see a way to properly include data structure problems. Take some Data Structure problem, it consists from two parts: <ul> <li> Knowing/implementing the Data Structure </li> <li> Actually thinking about the problem, and how this Data Structure...

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Pro Tips - get them while they are free More tips to use while studying under my tutoring [here](https://um-nik.notion.site/Pro-Tips-8b923b0dc7c94770824bdf4184afc43c). ## Stop caring about the rating Unless there are prizes involved, your position in the standings makes no difference. I can feel awful after winning a contest if I know that I could solve one more problem. Or I can feel OK losing a bunch of rating points knowing that I solved everything I could.  Because rating is just a number. It is highly volatile and it depends on other people, not only on your skill. But solving problems is totally up to you. And you should evaluate yourself not based on some random metric, but on your honest feeling whether you performed up to your expectations. Your sense of self should be under your control, don't get hung up on some imaginary value, you cannot reduce your progress to a single number. ## Don't use more than one account Rating is just a number. Do not be afraid to lose your colour. You’ll get it back in no t...

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Good Bye 2017 Hello everyone! Another year has gone by. The last Codeforces contest of this year will be tomorrow, [29 Dec, 15:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=12&year=2017&hour=18&min=35&sec=0&p1=166). The round details: - combined div1+div2 - 8 problems - 2.5 hours - rated!!! I'd like to thank the following people for helping with the round: [user:KAN,2017-12-28], [user:winger,2017-12-28], [user:AlexFetisov,2017-12-28], [user:zemen,2017-12-28], [user:xiaowuc1,2017-12-28], [user:MikeMirzayanov,2017-12-28]. Without them, this round would not have been possible. Scoring distribution will be posted later. Make sure to read ahead on the problems, since there may be some later problems that are easier for you. I hope to see you all at the contest, and good luck on the last chance to increase your rating this year! **EDIT1:** The scoring distribution is **500-750-1000-1750-1750-2000-2750-3500** **EDIT2:** There will be a five minute delay ...

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Codeforces Round #556 Hi Codeforces! I'm so happy to invite you to [contest:1149] and [contest:1150]! The rounds will be held on [contest_time:1149]. The round will be rated for both divisions. (At least that's what I've been told!) The problems were written and prepared by me. Thanks to [user:300iq,2019-04-27] for the round coordination, and to [user:Radewoosh,2019-04-27] for his invaluable help with choosing the problemset and testing the problems! Also, I want to give a shout-out to [user:MikeMirzayanov,2019-04-27] for his amazing Codeforces and Polygon platforms!  _My browser's tab bar, right now._ You'll work on **5** problems, and you will have **2** hours to solve them. The scoring distribution will be revealed closer to the round. ~~~~~ def get_end_remark(): return random.choice([ "Wish everyone high ratings!", "Good luck!", "Have fun!", "Please, read all the problems!"]) ~~~...

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Codeforces Round #703 (Div. 2) Hi, Codeforces! I finally get to return something to this great community, so I am glad to invite you to take part in [Codeforces Round #703 (Div. 2)](https://codeforces.com/contest/1486), which will take place on [contest_time:1486]. The round will be **rated for the participants with rating lower than 2100**. Participants from the first division are also welcomed to take part out of competition. You will be given **2 hours 15 minutes** to solve **6 problems**. All the problems were created and prepared by me. One of the problems is interactive, please read [the guide of interactive problems](https://codeforces.com/blog/entry/45307) before the contest. I would also like to thank: <ul> <li> [user:antontrygubO_o,2021-02-16] for excellent coordination! </li> <li> [user:1-gon,2021-02-16], [user:3EVEHAR_KOAVA,2021-02-16], [user:Akulyat,2021-02-16], [user:Aleks5d,2021-02-16], [user:BRCode,2021-02-16], [user:Osama_Alkhodairy,2021-02-16], [user:PO3OBAR_Bblnb,2021-02-16], [user:...

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Codeforces Round #683 by Meet IT (Div1, Div2) <img align="right" src="/predownloaded/5f/bf/5fbf2c3aae79d4f0d7e32a344f9478fb5ae825c2.png"> Hello, Codeforces! On behalf of Meet IT, I'm glad to invite you to ([Codeforces Round #683 by Meet IT (Div1, Div2)](https://codeforces.com/contests/1446,1447) which will take place [this Sunday (15th November)](https://www.timeanddate.com/worldclock/fixedtime.html?day=15&month=11&year=2020&hour=17&min=35&sec=0&p1=166). The round lasts 2.5 hours and is **rated** for both divisions. ### What is Meet IT? We are a family of enthusiastic and motivated young people passionate about programming and mathematics. We build a community where people learn together, motivate and help each other. <spoiler summary="Please expand the spoiler to find out more about us."> ### Our values - We teamwork, not compete, - Active learning is more effective than passive, - We all work on the same goal: a better education for everyone, - We don’t teach people; we show them how to discover b...

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Codeforces Round #497 by Skyglow <img style="float: right; margin: 0px 30px 20px 50px;" src="/predownloaded/7a/cb/7acb70215acb214185582e201c004419b1a7622f.jpg"> Hello, everyone! We are a Death Metal band [Skyglow](http://skyglowband.com/). Recently we released our first album. And since we happen to be sport programmers, we decided to make a Codeforces round in honor of this! The round will take place on [contest_time:1007]. There will be five problems for each division, three of them will coincide. The problems were made up by me and [user:SirRembocodina,2018-07-09], the contest was also prepared with the help of [user:TeaPot,2018-07-09], [user:GrumpyKitten,2018-07-09], [user:mingaleg,2018-07-09] and [user:niyaznigmatul,2018-07-09]. Thanks to [user:demon1999,2018-07-10] and [user:winger,2018-07-13] for testing, our coordinator [user:arsijo,2018-07-09] and, of course, [user:MikeMirzayanov,2018-07-09] for Codeforces and Polygon platforms. You can listen to the album by following the link: - https://skygl...

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Codeforces Round #743 Hello Codeforces! [user:Asymmetry,2021-09-16] and I are glad to invite you to [contest:1572] and [contest:1573], which will be held on [contest_time:1572]. Each division will have **6 problems** and **2 hours** to solve them. All problems were written and prepared by [user:Asymmetry,2021-09-16] and me. The round will be rated for both divisions. We would like to thank: - [user:1-gon,2021-09-16] for coordinating the round and helping us with the problems. - [user:mnbvmar,2021-09-16], [user:gamegame,2021-09-16], [user:dorijanlendvaj,2021-09-16], [user:tnowak,2021-09-16], [user:Jasiekstrz,2021-09-16], [user:ijxjdjd,2021-09-16], [user:shxgun,2021-09-16], [user:lcaonmst,2021-09-16], [user:-_-INV4D3R-_-,2021-09-16], [user:ToxicPie9,2021-09-16], [user:Shinchan01,2021-09-16] and [user:Krzaq,2021-09-16] for testing the round and providing useful feedback. - [user:ToxicPie9,2021-09-16] for being a VIP tester. - finally, [user:MikeMirzayanov,2021-09-16] for great platforms Codeforc...

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Codeforces Round #670 (Div. 2) Hello Codeforces! [user:gyh20,2020-09-10] and I are glad to invite you to [contest:1406] which will start on [contest_time:1406]. **Note the unusual start time of the round.** The contest will last for **two hours**, and you will have **five tasks** to solve. The tasks are prepared by me and [user:gyh20,2020-09-10]. This round is rated for participants whose **rating is not higher than 2099**. You can see that my current rating is exactly **2099** :) There might be an interactive problem. You can learn about them [here](https://codeforces.ml/blog/entry/45307). We would like to thank: - [user:isaf27,2020-09-10] for coordinating and helping us with the problems. - [user:namanbansal013,2020-09-10], [user:postscript,2020-09-10], [user:morzer,2020-09-10], [user:Osama_Alkhodairy,2020-09-10], [user:csani,2020-09-10], [user:growup974,2020-09-10], [user:physics0523,2020-09-10], [user:bizhouziwei20,2020-09-10] for testing the problems and providing useful feedback. Special thank...

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I might get stigmatized for this, but here it goes Recently, Moscow Fall Workshops has taken place (it ended about one week ago), and I wanted to address some issues that came into my mind during that period. As you might notice, it took me some time to build the courage and get in the right mindset to write about this. First of all, I want to say that I am a huge supporter of programming camps and, in general, initiatives to enhance the joy of doing competitive programming and I respect the efforts of building communities around CP. I have always had a kind of excitement when thinking about participating in programming camps (Petrozavodsk, Moscow Workshops, etc.) and their “hardcore” style with lots of contests. I therefore appreciate the immense efforts of organizers, problem setters, and testers, when preparing this camp. ### Main point Coming towards the main point of the blog, I felt that the last programming camp was a bit… underwhelming. Moreover, I’m having a hard time trying to justify the costs of doing such a camp,...

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Codeforces Round #796 Hi Codeforces! Happy Dragon Boat Festival! We are glad to invite you to our first Codeforces Round [contest:1687] and [contest:1688] which will be held on [contest_time:1687]. This round will be rated for participants of both divisions. Participants in each division will be offered 6 problems and 2 hours to solve them. The two divisions will share 3 problems. In this round, as the best friend of the characters in Touhou Project, you are going to help them solve the problems they meet. The problems are prepared by [user:xiaoziyao,2022-05-30], [user:Yakumo_Ran,2022-05-30], [user:SSerxhs,2022-05-30], [user:Cocoly1990,2022-05-30], [user:LilyWhite,2022-05-30], [user:Elegia,2022-05-30] and me. We hope you will enjoy this round. Great thanks to: - [user:74TrAkToR,2022-05-30] for good coordination of this round and translating all statements to Russian, - [user:Yakumo_Ran,2022-05-30] for providing most tasks, - [user:SSerxhs,2022-05-30] for preparing most tasks, - [user:L...

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Multiple accounts for one person should be banned Recently, There seems to be so many multiple accounts among various rating ranges. In top 10, there is [user:CongLingDanPaiShang3k5,2018-10-14], who became Legendary Grandmaster in 2 months. He should be a great genius, right? There is better hypothesis: He is someone's smurfing account. Everybody knows that [user:jiry_2,2018-10-14] = [user:Syloviaely,2018-10-14]. He performed quite a long ago, but it's the fact that he has multiple accounts, both having 2900+ ratings. In Div2 contests, many black-colored people are at top of the scoreboards. Why there are always a lot of talented newcomers? You will know the reason. Why don't Codeforces ban those multiple accounts? They ruins contest scoreboard and rating system. For example, [user:CongLingDanPaiShang3k5,2018-10-14] "absorbed" other participants rating for about 5-6 contests to be Legendary Grandmaster. On those contest's scoreboard, there were always him on top pages. One account for one person. That was the rule. Sm...

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Codeforces Round #934 (Div1, Div2) Hello Codech....err i mean Codeforces! I invite you to participate in [contest:1943] and [contest:1944] which will start on [contest_time:1943]. You will be given 6 problems and 2 hours 15 minutes to solve them in both divisions. Division 1 has $\textbf{2 subtasks}$, and Division 2 has $\textbf{1 subtask}$. Joining us on the problem setting panel are: - Coordinator: Ashley [user:errorgorn,2024-03-14] Khoo. - Authors: Satyam [user:satyam343,2024-03-14] Kumar Roy, Aditya [user:everule,2024-03-14] Jain, Shreyan [user:Dominater069,2024-03-14] Ray. - Russian Translation: Alexey [user:Alexdat2000,2024-03-14] Datskovskiy. - Red Testers: Kostia [user:kostia244,2024-03-14] Savchuk, Jeroen [user:jeroenodb,2024-03-14] Op De Beek, Andrei [user:andrei_boaca,2024-03-14] Boaca, Luan [user:LipArcanjo,2024-03-14] Arcanjo, Fernando [user:ffao,2024-03-14] Fonseca, Alexander [user:teraqqq,2024-03-14] Babin, Aleksei [user:Vercingetorix,2024-03-14] Esin, Zixuan [user:RDDCCD,2024-03...

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Codeforces Round #631 (Div. 1 and Div. 2) — Thanks, Denis aramis Shitov! Hello, everyone! [Codeforces Round #631](https://codeforces.com/contests/1329,1330) will be held at [contest_time:1329]. The problems are almost from me([user:dreamoon_love_AA,2020-04-01]), except one problem of which the idea is from [user:drazil,2020-04-01] and developed by me. Also we want to thank [user:300iq,2020-04-01] for helping me prepare the round, [user:isaf27,2020-04-01], [user:tmt514,2020-04-01], [user:rowdark,2020-04-01], [user:yp155136,2020-04-01], [user:wangyenjen,2020-04-01], [user:n_dao107,2020-04-01] and [user:zj713300,2020-04-01] for testing this round, and MikeMirzayanov for Codeforces and Polygon. This is my third time organizing a problemset for a Codeforces round (my previous rounds: [Codeforces Round #292](https://codeforces.com/contests/515,516), [Codeforces Round #320](https://codeforces.com/contests/578,579)). Good luck and have fun! **UPD**: Below is a message for you from [user:MikeMirzayanov,2020-04-02]: _About two weeks ago, we completed ...

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Algorithms Thread 9: Treaps (+ Gym Contest!) Algorithms Thread Episode 9: Treaps ================== Good morning everyone! [Episode 9 of AlgorithmsThread](https://youtu.be/6x0UlIBLRsc) comes out shortly after the Div2 round ends. This episode is on Treaps! It covers: - Fundamentals of Treaps - Splitting and Merging - Range reversing ... and more! I also decided to keep up the super-high quality style and made a [custom gym set](https://codeforces.com/gym/102787) with 5(+2) original problems to make sure you really understand everything that was covered in the lecture. The gym set will be released shortly after the lecture ends, and I hope that the problems will be challenging and fun, even for people who aren't seeing treaps for the first time. If you have any questions or suggestions, feel free to leave them below. I hope you enjoy the problem statements, and, in the spirit of the upcoming holiday, I'll leave you all with this:  <hr /> Update:...

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Editorial of Global Round 11 #### General comments Broadly speaking, problems A-B-C-D were "div2 problems", while F-G-H were "strong grandmaster problems" (with E staying in the middle). I did not expect anyone to solve all the problems and thus I decided to give the scoring F+G=H (so that maybe someone would have solved H). <br><br> Many of the problems (A, C, D, E, G) admit multiple solutions. Sometimes the core of the solution is the same (C, D) and sometimes the solutions are truly different (A, E, G). <br><br> If you are an experienced participant, I would like to hear your opinion on the problems. Feel free to comment on this post or send me a private message. <br><br> <spoiler summary="Overview of the problemset" > The easiest problem of the contest, *A-Avoiding Zero*, is about rearranging an array of numbers. It is intended as a very easy problem that still requires to think. Then, in *B-Chess Cheater* an intuitive (but nontrivial to prove) greedy approach is the way to go. *C-The Hard Work of P...

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Codeforces Round #630 (Div. 2) Hello Codeforces! I am glad to invite you to my first official round [contest:1332], which will take place on [contest_time:1332] **(please note for the unusual starting time)** and will be rated for **all Division 2 participants**. You will be given **7 tasks** and **150 minutes** to solve them. All tasks in this round were prepared by me. Hope that you will enjoy those tasks! I would like to thank: - [user:pikmike,2020-03-29] for great coordination of this round, and the idea of solution of one task! - [user:Nanako,2020-03-29], [user:nezzar,2020-03-29] for useful discussion and testing this round! - [user:antontrygubO_o,2020-03-29], [user:McDic,2020-03-29], [user:vovuh,2020-03-29], [user:Flowerandyouth,2020-03-29], [user:socho,2020-03-29], [user:Oak_limy,2020-03-29], [user:Amori,2020-03-29], [user:Stresshoover,2020-03-29], [user:I1I1I11I1I1,2020-03-29], [user:defolaut,2020-03-29], [user:hx073269,2020-03-29] and [user:Pavlova,2020-03-29] for testing this round and...

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Codeforces Round #290 Fox Ciel is back! I invite you to participate in Codeforces Round #290, which will start at the [standard time on next Monday](http://www.timeanddate.com/worldclock/fixedtime.html?day=2&month=2&year=2015&hour=19&min=30&sec=0&p1=166): This is my 4th round on Codeforces, my previous rounds: [#190](http://codeforces.com/blog/entry/8163), [#228](http://codeforces.com/blog/entry/10605), [#270](http://codeforces.com/blog/entry/13997). Last Div1 Round ([#286](http://codeforces.com/blog/entry/15842)) is so hard, so after notice that, we decide to reduce the difficulty of this round. (For example, current Div1-E was used as Div1-D) I hope more people can enjoy all tasks in this round: this time no task requires advanced knowledge like linear space or Fourier Transform. The background story will be Fox Ciel's life: learning programming, play games, traveling, have dinner and so on. Like Round [#228](http://codeforces.com/blog/entry/10605), top-20 contestants that are currently at...

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I am removing my contest proposal from Codeforces I am removing my contest proposal from Codeforces. Note: This is a serious blog post. Also, the opinions presented in this blog are my own and not of my friend [user:BiIIy,2018-12-26] who wrote the contest with me. Today I have removed my contest proposal from Codeforces. I should probably have done this a long time ago. The proposal was made in February, but the problems were written and finished by March, and that is when I opened the contest proposal for review and messaged [user:KAN,2018-12-26]. It is currently December and no progress or development has been made regarding my contest proposal since, so I will be removing it. I have multiple reasons for removing my contest proposal: - I have no motivation to host an online contest anymore. - I am involved in problem setting with two other high school programming contests in my university, and I write, host, and judge another contest for local high schools. - I have forgotten that I “was in the queue” for writing a...

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Codeforces Round #669 [user:realhype,2020-09-06] and I are glad to invite you to [contest:1407], which will take place on [contest_time:1407]. **The round will be rated for all the participants with rating strictly less than 2100.** The problems were created and prepared by [user:realhype,2020-09-06] and [user:i.e,2020-09-06]. We would also like to thank everyone who was involved in the round preparation: - [user:antontrygubO_o,2020-09-06] for round coordination and high sense of taste that made our contest IDEAl. - [user:xiryss,2020-09-06], [user:Tlatoani,2020-09-06], [user:hugopm,2020-09-06], [user:Alireza_Keshavarz,2020-09-06], [user:jouIej,2020-09-06], [user:jo_ulej,2020-09-06], [user:dick,2020-09-06], [user:Ari,2020-09-06], [user:AmShZ,2020-09-06], [user:AliceWalkingOutOfHerLife,2020-09-06], [user:Devil,2020-09-06], [user:morzer,2020-09-06], [user:baby_baby_baby_ooh,2020-09-06], [user:PM11,2020-09-06], [user:postscript,2020-09-06], [user:Programmer,2020-09-06], [user:saurabhshadow,2020-09-06],...

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Codeforces Round #673 **As-salamu alaykum**, Codeforces! (Peace, Codeforces!) We are glad to invite you to [contest:1416] and [contest:1417], which will take place at **[contest_time:1416]** (notice **later** time than usual). The round is **rated** for both divisions. Each division will be given 6 problems to solve in 2 hours. Problems were prepared by [user:RedDreamer,2020-08-05], [user:BThero,2020-08-05] and me [user:DimmyT,2020-09-25]. We are very grateful and would like to sincerely thank the following people for their assistance in preparing the round: - [user:BledDest,2020-08-31] for the brilliant coordination of our round. - [user:adedalic,2020-08-28], [user:kdjonty31,2020-08-28], [user:PM11,2020-08-28], [user:namanbansal013,2020-08-28], [user:RockyB,2020-08-28], [user:postscript,2020-08-28], [user:saurabhshadow,2020-08-28], [user:morzer,2020-08-28], [user:Mohamed.Sobhy,2020-08-28], [user:growup974,2020-08-28], [user:hugopm,2020-08-28], [user:Tlatoani,2020-08-28], [user:dorijanlendvaj...

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Codeforces Round #772 (Div. 2) Hello, Codeforces! [user:dannyboy20031204,2022-02-18] and I are glad to invite everyone to participate in [contest:1635], which will be held on [contest_time:1635]. **This Round will be rated for participants with rating lower than 2100.** You will have **2 hours** to solve **6 problems**. We would like to thank: - [user:74TrAkToR,2022-02-18] for excellent coordination of the round and translating the statements. - [user:mhq,2022-02-18], [user:generic_placeholder_name,2022-02-18], [user:null_awe,2022-02-18], [user:ptd,2022-02-18], [user:Fysty,2022-02-18], [user:8e7,2022-02-18], [user:yungyao,2022-02-18], [user:Devil,2022-02-18], [user:amano_hina,2022-02-18], [user:Dragonado,2022-02-18], [user:DIvanCode,2022-02-18], [user:voventa,2022-02-18], [user:lox123,2022-02-18], [user:Marslai24,2022-02-18], [user:FHVirus,2022-02-18], [user:saarang,2022-02-18], [user:Olly_Z,2022-02-18], [user:arseny.__.,2022-02-18], [user:Prokhor08,2022-02-18], [user:sam571128,2022-02-18], [user:efimovpau...

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Codeforces Round #659 Hello, Codeforces! I'm very glad to invite you to the first **Cuban round** [contest:1383] and [contest:1384] which will take place on [contest_time:1383]. All problems in this round were created and prepared by [user:marX,2020-07-21], [user:gilcu3,2020-07-21], [user:dcordb,2020-07-21], [user:jcg,2020-07-21] and me. We tried to make them interesting and diverse and hope that you will enjoy them! You will be given **2 hours** to solve **6 problems** in both divisions, and we **highly** encourage you to read all of them :) We would like to thank: - [user:antontrygubO_o,2020-07-21] for amazing coordination of this round. - [user:Um_nik,2020-07-21], [user:gamegame,2020-07-21], [user:ffao,2020-07-21], [user:eatmore,2020-07-21], [user:isaf27,2020-07-21], [user:balbit,2020-07-21], [user:Tlatoani,2020-07-21], [user:Prabowo,2020-07-21], [user:Kuroni,2020-07-21], [user:hugopm,2020-07-21], [user:MagentaCobra,2020-07-21], [user:qlf9,2020-07-21], [user:faremy,2020-07-21], [use...

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Community IOI Weekly Classes (on Codechef?) Let's discuss the idea of IOI preparation in form of weekly contests and classes. Many programming camps reuse problems from old national camps and contests. What about doing this on a bigger scale and conducting weekly mashup contests open for everybody for free? The problem analysis would be in English, in written or (live) video format, possibly combined with a lecture. Make a discord server for further discussion and questions, encourage students to upsolve, maintain yearly leaderboard and upsolving leaderboard. Once or twice a year, call it a 1-week online camp and organize these mashup contests daily. I can take part in this initiative but I want to be just one of many teachers. When it's my turn, I would pick some old interesting POI or ONTAK problems because I either know them or can look up the solution in Polish. If I do this once per 1-2 months, I won't run out of good problems anytime soon, and I have enough time to prepare analysis and lecture, and later spend severa...

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Dasha Code Championship Finals and Mirror Round 588 Announcement Hello everybody! A new round is upcoming and I'm honored to be its author. The round will first appear as the onsite for Dasha.AI Code Championship and later we will hold a rated mirror. Everybody is welcomed to participate in Codeforces and I wish good luck for people in Saint Petersburg and Novosibirsk. Using the opportunity, I want to thank: - [user:mnbvmar,2019-01-02] for helping in the preparation of a great part of everything. Really, without you, I wouldn't do it. - [user:300iq,2019-01-02] for coordination and help with preparation. - As always, [user:MikeMirzayanov,2019-01-02] for taking care of international competitive programming and making such great platforms as Codeforces and Polygon. - [user:KAN,2019-09-24], [user:zscoder,2019-09-24], [user:Lewin,2019-09-24], [user:JeffreyHo,2019-09-24], [user:Darkstalker,2019-09-24], [user:Darko,2019-09-24] and [user:Gtaumaturgo,2019-09-24] for testing the problems and great advice. - [Dasha.Ai](https://dasha.ai/en/) for an or...

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Codeforces Round 794 Announcement We will hold [contest:1685] and [contest:1686]. <ul> <li> Contest URLs: <a href="https://codeforces.com/contest/1685">https://codeforces.com/contest/1685, <a href="https://codeforces.com/contest/1686">https://codeforces.com/contest/1686 </li> <li> <b> Unusual </b> start time: [contest_time:1685] </li> <li> Duration: 135 minutes </li> <li> Number of Tasks: 6 for Div2, 5 for Div1 </li> <li> Rated range: $(-\infty, 1899]$ for Div2, $[1900, \infty)$ for Div1 </li> <li> Writer: [user:antontrygubO_o,2022-05-22] </li> <li> Testers: [user:golions,2022-05-22], [user:oleh1421,2022-05-22], [user:Geothermal,2022-05-22], [user:nor,2022-05-22], [user:TheScrasse,2022-05-22], [user:timreizin,2022-05-22], [user:emorgan5289,2022-05-22], [user:Um_nik,2022-05-22], [user:mhq,2022-05-22], [user:Kuroni,2022-05-24], [user:ak2006,2022-05-24] </li> <li> VIP-tester: [user:errorgorn,2022-05-22] </li> <li> Coordinator and author of one problem without which round would be unbalanced: [user:dario...

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VK Cup 2017 Round 1 and CF Round 405 div1+div2 Hello. The round 1 of VK Cup 2017 will take place on March 18 at 18:35 MSK (check your timezone [here](https://www.timeanddate.com/worldclock/fixedtime.html?day=18&month=3&year=2017&hour=18&min=35&sec=0&p1=166)), along with standard div1+2 Codeforces Round \#405. The contest "VK Cup 2017 &mdash; Round 1" is for teams qualified from two Qualification Rounds. The top 400 teams will advance to the Round 2, while other ones will have one more chance in the Wild Card Round 1 in April. Those who don't participate in the VK Cup can take part in the Codeforces Round \#405 individually (problems will be available in English too). All three rounds last 2 hours, and all are rated. I want to thank: [user:KAN,2017-03-17] for his help in the contest preparation, [user:MikeMirzayanov,2017-03-17] that we are here, [user:AlexFetisov,2017-03-17] for testing, the VK company for this nice annual contest. I'm a setter and I hope (and expect?) that you will enjoy the problems. During the conte...

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Codeforces Round #270 Do you want to win a T-shirt? Do you want to learn how to design tasks for programming contest? Do you want to solve 7 tasks in 2.5 hours? So Codeforces Round #270 is right for you. It was designed by me in California, Assembled in polygon (so Thank you [user:MikeMirzayanov,2014-09-26] for the system and [user:Gerald,2014-09-26] for organize and testing), will start on [regular time this Sunday](http://www.timeanddate.com/worldclock/fixedtime.html?day=28&month=9&year=2014&hour=19&min=30&sec=0&p1=166), don't miss it! The organizers of **<a href="/blog/entry/13929">Marathon24</a>** decided to present gifts to the best finishers of the round! Best 25 participants will get Marathon24 tshirts! Thanks! <center> <img src="http://www.elmostshirts.com/images/tshirts.jpg"/> <br><small>It is just an image to attract your attention. Real tshirts will be designed specially for Marathon24!</small> </center> There are some articles introduced how to become a problem setter, like [Pro...

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Codeforces Round #632 (Div. 2) Hello, Codeforces! I'm glad to invite you to my first round [contest:1333], which will take place on [contest_time:1333]. "Thank you" time! I'd like to thank: - [user:antontrygubO_o,2020-04-05] for coordination of the round. - [user:300iq,2020-04-05], [user:nvmdava,2020-04-05], [user:aryanc403,2020-04-05], [user:antoshkin,2020-04-05], [user:lkosten,2020-04-05], [user:pavel-afonkin,2020-04-05] for testing and useful advices. - [user:MikeMirzayanov,2020-04-05] for great systems Codeforces and Polygon. - [user:CuriOusQuOkka,2020-04-05] for listening to my mumble while I came up with tasks. - [user:antontrygubO_o,2020-04-05] for coordination of the round (again). You'll be given 6 problems and 2 hours to solve them. Point distribution will be announced as soon as possible. Hope you will enjoy the round! Good luck and have fun! **P.S: YES, IT'S RATED.** **UPD**: Score distribution: 500 &mdash; 750 &mdash; 1250 &mdash; 1750 &mdash; 2000 &mdash; 2500. **U...

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Codeforces Round #729 (Div. 2) Hello Codeforces! [user:tianbu,2021-07-01] and I are glad to invite you to [contest:1542] which will start on [contest_time:1542]. **Note the unusual start time of the round.** The contest will last for **two hours**, and you will have **five tasks** to solve. The tasks are prepared by [user:tianbu,2021-07-01] and me. This round is rated for participants whose **rating is not higher than 2099**. We would like to thank: - [user:Aleks5d,2021-07-01] for coordinating and helping us with the problems. - [user: dorijanlendvaj,2021-07-01], [user:waaitg,2021-07-01], [user:Imakf,2021-07-01], [user:alexX512,2021-07-01], [user:Akulyat,2021-07-01], [user:talibmohd,2021-07-01], [user:LostCoder16,2021-07-01], [user:andr0901,2021-07-01], [user:nnv-nick,2021-07-01], [user:Delmos,2021-07-01], [user:kassutta,2021-07-01], [user:m371,2021-07-01], [user:4qqqq,2021-07-01], for testing the problems and providing useful feedback. - [user:amgfrthsp,2021-07-03] for translating the statem...

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Good Bye 2014 Hi, Codeforces! Welcome to the last Codeforces Round of 2014, **Good Bye 2014**! This round is *very unusual*; First, the round starts at **[December 30th, 18:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Good+Bye+2014&iso=20141230T18&p1=166&ah=2&am=30)**. Second, the round lasts for **2.5 hours**. And lastly, the round will be **division combined**, which means Div1 contestants and Div2 contestants won't be separated. The problems are prepared by me ([user:tncks0121,2014-12-29]) and Seunghyun Jo ([user:ainta,2014-12-29]). This is our second round at Codeforces. Because our first round caused(?) [the Black Day](http://codeforces.com/blog/entry/10683), we hope this round won't cause any errors like before :D Thanks to Won-seok Yoo([user:ainu7,2014-12-29]), who tested our round and gave us comments about the problemset. We'd like to thank some people who were necessary to make this round: Maxim Akhmedov ([user:Zlobober,2014-12-29]) gave us great help prepar...

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Opinion: Don't Waste Problems on Div 2 **History Lesson** Let's take a look at the solve count for the last problems in the last 4 division 2 contests: 803 (Div. 2): F (7 official solves); G (2 official solve) 802: E (18 official solves): F (11 official solves) 801: E (1 official solve) Edu 130: F (2 official solves) There's a trend. The last and hardest div2 problem frequently has very few official solves. This means that the last problem, despite taking a lot of time to create, doesn't really affect rankings that much. The authors spent much time for a problem that didn't make a big difference. But it would've made a difference in div1. Personally, I think that it's okay if 20 or even 30 people AK a div2 round, so it's okay to have 20-30 people solving the last problem. Then, you can take those hard problems and insert them into a div1 round. That way, we can have more contests. Basically, make div2 last problems a little easier, that way we can save those hard problems for another contest. What...

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Lowerbound for div2 While I have mixed feelings about division 4, I think it perfectly matches introducing the rating lowerbond in division 2. Maybe 1501 is a good idea, I'm not sure. Or maybe let new participants have 1400 initially (upper bound for div4) and lowerbound for div2 would be 1401. The benefits are decreased load for the main and rare div1+2 rounds, and possibility to slightly increase the difficulty of div2-abc, thus get back to the format with 5 problems per division (3 are common). Because the contest is then for a group of people with more similar skill level. These arguments aren't that important for div2-only contests so it's ok if those are without lowerbound, I don't care. Or make those div2+3 instead of div2-only, I again don't care.

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Codeforces Round #912 (Div. 2) Γεια σου (Hello), Codeforces once again! [user:Adam_GS,2023-11-25] and I are glad to invite you to participate in [Codeforces Round #912 (Div. 2)](https://codeforces.com/contest/1903) which will take place on [contest_time:1903]. **Note the unusual start time of the round**. As usual, **this round will be rated for participants with rating lower than 2100.** Problems were created and prepared by [user:Adam_GS,2023-11-25] and me. We tried to make them interesting, with short and clear statements. We hope that you will enjoy them! I would like to thank: - [user:ScarletS,2023-11-25] for amazing coordination of this round. - [user:Adam_GS,2023-11-25] for joining as an author after testing the contest. - [user:fishy15,2023-11-25], [user:Andreasyan,2023-11-25], [user:phattd,2023-11-25], [user:Murinh0,2023-11-25], [user:irkstepanov,2023-11-25], [user:wuhudsm,2023-11-25], [user:Ari,2023-11-25], [user:satyam343,2023-11-25], [user:Qualified,2023-11-25], [user:nyaruhod...

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LGMSniper.com: See which LGMs you have beaten! LGM Sniper ================== I just created a cool CF tool called [LGM Sniper](https://wumbogames.com/CompetitiveProgramming/LGMSniper). It looks at scoreboard data from every Div1 and Div1+Div2 round ever and tells you which LGM's you have beaten, how many times you have beaten them, and which rounds you beat them in. You can also compare yourself to your friends to see which one of you wins more! If you want to compare yourself with some friends, check the 'show ex-lgms' box and enter the friend you want to compare to as Handle #2, and they will show up on the bottom. You can try it out for yourself at [lgmsniper.com](https://wumbogames.com/CompetitiveProgramming/LGMSniper), or in the competative programming section of [Wumbo Games](https://wumbogames.com/), if you would prefer. Tooltips show the name of the rounds you won in (hover your mouse over the checkmark). If you find any interesting facts or have suggestions for how I could improve the tool, let me know in the co...

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Codeforces Round #699 (Div. 2) Hi fellow Coders! [user:Shanks,2021-02-02], [user:Salem_Alwarawreh,2021-02-02] and I are glad to invite you to take part in [contest:1481], which will take place on [contest_time:1481]. Round will be rated for participants with rating less than 2100. Participants from the first division are also welcomed to take part out of competition. You will be given **2 hours** to solve **6 problems**, each problem has a picture and a story above it. The stories are skippable if you want to focus on the real problems. We would also like to thank: - [user:adedalic,2021-02-02] for the coordination and discussion of this round! - [user:Motarack,2021-02-02], [user:namanbansal013,2021-02-02], [user:Jellyman102,2021-02-02], [user:stack_overflows,2021-02-02], [user:Manik,2021-02-02], [user:morzer,2021-02-02] and [user:_HossamYehia_,2021-02-02] for phase one testing and valuable feedback. - [user:kclee2172,2021-02-02], [user:awoo,2021-02-02], [user:Karavaiev,2021-02-02], [user:I_Love_YrNameC...

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Codeforces Round #676 (Div. 2) Hi Codeforces! [user:stefdasca,2020-10-17], ~koala_bear00,2020-10-14 and I are very excited to announce our first contest [Codeforces Round #676](https://codeforces.com/contest/1421), which will take place [contest_time:1421]. The round will be rated for participants with rating up to 2099. The tasks were written by me with help from [user:stefdasca,2020-10-14] and [user:koala_bear00,2020-10-14] and you have to help some of the authors' favorite musical artists to solve the problems they're faced with. We hope we compiled a very interesting contest with memorable tasks :) Special thanks to: * [user:antontrygubO_o,2020-10-14] for coordinating our round and pushing us to come up with more and more interesting tasks. * [user:dorijanlendvaj,2020-10-14], [user:kclee2172,2020-10-14], [user:Devil,2020-10-14], [user:thenymphsofdelphi,2020-10-14], [user:jainbot27,2020-10-14], [user:Stelutzu,2020-10-14], [user:proggerkz,2020-10-14], [user:SleepyShashwat,2020-10-14], [user:bh...

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Codeforces Round #721 (Rated for Div2) Hi, Codeforces! I'm glad to invite you to take part in [Codeforces Round #721 (Div. 2)](https://codeforces.com/contests/1527), which will take place on [contest_time:1527]. The round will be **rated for the participants with a rating lower than 2100**. Participants from the first division are also welcomed to take part in the competition but it will be unrated for them. You will be given **2 hours** to solve **5-6 problems**. Problems were created by members of Club of Programmers IIT (BHU)- [user:rivalq,2021-05-18], [user:sharabhagrawal25,2021-05-18], [user:loud_mouth,2021-05-18], [user:DenOMINATOR,2021-05-18], [user:Bignubie,2021-05-19], [user:mallick630,2021-05-18], [user:shikhar7s,2021-05-18], [user:CoderAnshu,2021-05-19] and Me. Huge thanks to those who helped make this round possible: - [user:Aleks5d,2021-05-18] and [user:KAN,2021-05-18] for their excellent coordination and for providing priceless feedback during contest creation. - [user:1-gon,2021-05-18], [u...

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Codeforces Round #800 Hi Codeforces! [user:Keshi,2022-06-13], [user:alireza_kaviani,2022-06-13] and I are delighted to invite you to participate in [contest:1693] and [contest:1694]. - Start time: [contest_time:1693] - Duration: $120$ minutes - Number of Tasks: $6$ for both divisions - Rated range: ($-\infty$,$1899$] for Div2, [$1900$, $\infty$) for Div1 We are honored to have set the 800th Codeforces round. We wish this wonderful platform all the best along with many other exciting rounds. Huge thanks to the following people: - [user:antontrygubO_o,2022-06-13] for his breath-taking coordination. - Our testers [user:um_nik,2022-06-13], [user:errorgorn,2022-06-13], [user:koosha_mv,2022-06-13], [user:irkstepanov,2022-06-13], [user:ArchUser84,2022-06-13], [user:sohsoh,2022-06-13], [user:fatemetmhr,2022-06-13], [user:Dorost,2022-06-13], [user:nor,2022-06-13], [user:pooya-shams,2022-06-13], [user:Arnch,2022-06-13], [user:Kahou,2022-06-13] and [user:mosaev,2022-06-13] for testing the round an...

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Invitation to CodeChef December Lunchtime 2020 We invite you to participate in CodeChef’s [December Lunchtime](http://bit.ly/LTIME91-Codeforces), this **Saturday, 26th December**, from [9:30 pm to 12:30 am IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=December+2020+Lunchtime&iso=20201226T2130&p1=44&ah=3). **Note the unusual time.** It starts at 9:30pm instead of the usual 7:30pm You will be given a total of **8 problems** (6 in Div2, 6 in Div1) to solve in a duration of **3 hours**. Joining us on the problem setting panel are: - Setters: Sahil [user:sahi1422,2020-12-25] Chimnani, Venkata [user:Nikhil_Medam,2020-12-25] Nikhil Medam, Áron [user:mraron,2020-12-25] Noszály, Nishant [user:nishant403,2020-12-25] Shah, Yogesh [user:SeismicToss,2020-12-25] Sharma, Hriday [user:the_hyp0cr1t3,2020-12-25], Divyam [user:divyamsingal01,2020-12-25] Singal, Bhavyesh [user:bhvdsi,2020-12-25] Desai - Tester: Rahul [user:amnesiac_dusk,2020-12-25] Dugar - Editorialist: Taranpreet [user:taran_1407,2020-12-25] Singh ...

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About the Codeforces Round #637 Hello Codeforces. I'm writing this post to make comments about a situation on the last Codeforces Round and tell the bad news. We did many mistakes and due to them, the round caused much dissatisfaction from the Codeforces community. Some of our mistakes: 1. Some stupid mistakes in the statements. 2. In the problem D2E/D1C the numbers $d_i$ were not necessarily sorted, but there were no pretests for that. 3. The checker of the problem D2F/D1D didn't check one of the requirements and due to that $8$ solutions failed on pretests during the system testing. 4. After the editorial was posted the mistake was found in the main solution of the problem D1E ([more details here](https://codeforces.com/blog/entry/76479?#comment-609911)). Now we don't know the correct solution. So, the round was very unsuccessful, I'm very sorry about this. I will make conclusions and will try to avoid such situations later. Please, treat with respect to the authors, even in such a bad situatio...

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Codeforces Round #318 [RussianCodeCup Thanks-Round] Hello Codeforces community! Codeforces Round #318 (for both divisions) will take place on [August, 29 at 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=8&year=2015&hour=19&min=30&sec=0&p1=166). It is the Thanks-Round devoted to Russian Code Cup. You will be given 5 problems and 2 hours to solve them. Scoring will be announced close to the round. I strongly recommend you to read all problems.  <a href="http://www.russiancodecup.ru/">RussianCodeCup</a> is the largest open programming competiton for Russian-speaking participants by Mail.Ru Group. Its history started in 2011. And since the first championship RCC offers great problems and generous prizes. This year finals will be held on September, 19th. Wish good luck to all the finalists! Thank you, RussianCodeCup, for your gift on the 5th anniversary of Codeforces! I am honoured to be a problem setter ...

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Codeforces Round #851 (Div. 2) Hello Codeforces and welcome back to another div2 round. [user:YeongTree,2023-02-06] and I are excited to invite everyone to participate in [contest:1788], which will be held on [contest_time:1788]. This round is rated for the participants with ratings strictly lower than **2100**. You will be given **6 problems** and **2 hours** to solve them. All the problems are authored and prepared by [user:YeongTree,2023-02-06] and me. We would like to thank - [user:Arpa,2023-02-06] for excellent coordination and help with prepration. - [user:Alexdat2000,2023-02-06] for Russian translation. - [user:tlsdydaud1,2023-02-06], [user:hypergraph_coloring,2023-02-06], [user:Kawaii2DIdolOfGSHS,2023-02-06], [user:nlog,2023-02-06], [user:Ryute,2023-02-06], [user:TheQueenOfHatred,2023-02-06], [user:hanbyeol_,2023-02-06], [user:Physics07,2023-02-06], [user:jjang36524,2023-02-06], [user:OctaneC8H18,2023-02-06], [user:ahgus89,2023-02-06], [user:DELTARUNE,2023-02-06], [user:Go3,2023-02-06], [user:a...

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Codeforces Round #356 Hello Codeforces. The CF Round \#356 will happen on 8-th June ([exact time](http://www.timeanddate.com/worldclock/fixedtime.html?day=8&month=6&year=2016&hour=19&min=35&sec=0&p1=166)). You will get five problems to solve in two hours. The round is rated. I encourage you to read other problems if you don't like or can't solve something. The scoring distribution will be announced. [user:MikeMirzayanov,2016-06-06] and [user:GlebsHP,2016-06-06] make the round possible. Also, thanks for [user:Stonefeang,2016-06-06], [user:kostka,2016-06-06], [user:johnasselta,2016-06-06], [user:AlexFetisov,2016-06-07] and (more to be added?) for their amazing help. And I want to thank my girlfriend because there would be no Limak without her. It's my first standard round. Still, you should get nice interesting problems. You will meet Limak, who is usually a little polar bear. Here he is, preparing one of problems. ![ ](http://codeforces.com/predownloaded/91/95/91956cb0e92e3c0376634a6a1...

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Codeforces Round #462 Hi, Codeforces! Happy Valentine's Day. And happy Lunar New Year! I'm quite honored to invite you to Codeforces Round #462 which will take place at [15:05 MSK on 14 Feb](https://www.timeanddate.com/worldclock/fixedtime.html?day=14&month=2&year=2018&hour=15&min=5&sec=0&p1=166) and last for two hours. The authors are [user:quailty,2018-02-12], [user:skywalkert,2018-02-12], [user:visitWorld,2018-02-12] and me. This is our second round here. The round couldn't have been realized without efforts of [user:KAN,2018-02-12] and our testers: [user:cyand1317,2018-02-12], [user:demon1999,2018-02-12]. Thanks for your help to the contest. Also, thank [user:MikeMirzayanov,2018-02-12] for the fantastic Codeforces and Polygon platforms. The contest will consist of five problems and it is **rated** for both division contestants. The background of problems will be about Lunar New Year. (Yes... Not Valentine's Day...) Hope to see you in the contest! Good luck and have fun, wish you a hig...

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SWERC 2021-2022 <img src="/predownloaded/4a/fc/4afcde700751b1ef849737c2edd64e52901e8df3.png" style="width:250px; float:right; margin: 0 1em 1em 1em"/> The Southwestern Europe Regional Contest will take place on the 23rd of April. It is the ICPC regional contest (i.e., the winning teams will advance to the ICPC World Finals) for teams from France, Israel, Italy, Portugal, Spain, and Switzerland. The mirror contest [contest:1662] will be held on Codeforces at [contest_time:1662] and will last 5 hours. The mirror contest will contain all the problems from the official competition plus some additional problems. I am the chief judge for the competition and I want to thank: - The amazing set of judges who proposed and prepared the problems: [user:cescmentation_folch,2022-04-04], [user:cip999,2022-04-04], [user:Delfad0r,2022-04-04], [user:gangsterveggies,2022-04-04], [user:giove,2022-04-04], [user:gog.gerard,2022-04-04], [user:majk,2022-04-04], [user:Petr,2022-04-04], [user:Simon,2022-04-04...

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Новый координатор представляет Codeforces Round #327 Здравствуйте, уважаемые участники сообщества Codeforces! Начиная с Codeforces Round #327, я буду координировать подготовку регулярных раундов и прочих контестов, которые проводятся на платформе Codeforces. Обещаю приложить максимум усилий, чтобы улучшить качество подготовки контестов, хотя это и будет проблематично сделать &mdash; [user:Zlobober,2015-10-24] установил высокую планку. Давайте ещё раз поблагодарим Максима за хорошо проделанную работу! Завтрашний раунд проводится на задачах Московcкой городской командной олимпиады по программированию среди школьников. Пусть вас не смущает, что это школьное соревнование, &mdash; среди участников есть золотой призёр IOI 2015 и несколько кандидатов в сборную России этого года, поэтому мы постарались сделать все задачи интересными, а некоторые ещё и сложными. Уверен, что каждому из вас должна понравиться хотя бы одна задача предстоящего раунда. Задачи были подготовлены коллективом московских авторов в составе (список пополняется): [us...

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Codeforces Round #190 Hello, everyone! Do you want to train your skill by a contest before [ACM/ICPC Finals](http://icpc.baylor.edu/worldfinals)? Codeforces Round #190 will take place on [Friday, June 28th at 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23190&iso=20130628T1930&p1=166&ah=2). This is the last chance to practice, don't miss it! I am [user:cgy4ever,2013-06-26] from China, and this is my first round on Codeforces, I hope you will love it. As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. I am the writer of them. And I would like to thank [user:Gerald,2013-06-26] and [user:sdya,2013-06-26] for testing, and [user:MikeMirzayanov,2013-06-26] for the Codeforces project including [polygon](http://codecenter.sgu.ru/polygon/home) system. Good luck and have fun! **Update 1**: The score distribution for Both Division is regular (500-1000-1500-2000-2500). The main character of all problem will be: Fox Ciel. (See [here](http...

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CodeCraft-21 and Codeforces Round #711 (Div. 2) Hello all! We are proud to invite you to **CodeCraft-21**, which takes place on [contest_time:1498]. It is rated for all Div2 participants (rating under 2100). This contest comes under **Threads'21**, as a part of our annual techno-cultural fest [Felicity, IIIT Hyderabad](https://felicity.iiit.ac.in). We have **special prizes for Indian participants**! <img src="/predownloaded/8e/0a/8e0a76faf6acc96ba6ffb9b873136259066b5211.png" width="450px"> You will be given **six problems** to solve in a duration of **two hours**. We have tried our best to keep clean statements, useful samples with good explanations, and strong pretests! We have written step-wise editorials, and will also release video editorials! We would like to thank these amazing people for helping make the contest happen: - [user:bleddest,2021-03-27] for great coordination of our round - [user:ninja_28,2021-03-27], [user:dixitgarg,2021-03-27], [user:ltc.groverkss,2021-03-27] and myself for amazing problem...

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Codeforces Round #282 Hi, Codeforces Round #282 will be held at [13th of December, 19:30 MSK](http://timeanddate.com/worldclock/fixedtime.html?day=13&month=12&year=2014&hour=19&min=30&sec=0&p1=166). Please don't note anything since the time is the usual time of contests. The round is prepared by [user:FarbodY,2014-12-12], [user:Haghani,2014-12-12] and Me([user:matrix,2014-12-12]). We'd like to thank [user:Zlobober,2014-12-12] who helped us a LOT for preparing the problems, [user:MikeMirzayanov,2014-12-12] for the Polygon and Codeforces platforms and [user:delinur,2014-12-13] for helping us in preparing statements and translating them. Our special thanks goes to [user:mruxim,2014-12-12] for testing the round. The problems will be sorted according to the estimated order of difficulty according to our opinion but we strongly recommend you to read all of the problems. As always the update regarding score distribution will be posted **just** before the round starts. :) **UPD**: It was writ...

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VK Cup 2016 — Round 3 Hi everybody. The VK Cup Round 3 is coming ([exact time](http://www.timeanddate.com/worldclock/fixedtime.html?day=7&month=5&year=2016&hour=18&min=5&sec=0&p1=166)). The duration will be longer than usual, likely 3 hours. As usually in VK Cup, there will be three contests &mdash; div1, div2, official one. All of them are rated. Div1 and div2 versions are for individual participants, not for teams. Setters are [user:Stonefeang,2016-05-05], [user:Errichto,2016-05-05] and [user:qwerty787788,2016-05-05]. I think that (some) problems are extremely interesting and I really wish I could participate. Thanks to [user:GlebsHP,2016-05-05] and [user:MikeMirzayanov,2016-05-05], we wouldn't have a round without them. Also, thanks to [user:AlexFetisov,2016-05-06] and [user:winger,2016-05-06] for testing. We will later inform about the final duration. Maybe we will inform about the number of problems and scoring. I wish you great fun and no frustrating bugs. And Limak wishes you...

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Codeforces Round #503 (based on SIS olympiad) Hi! _Summer Informatics School (SIS / LKSH) is a summer school for students in grades 6-10. SIS is focused mainly (but not only) on students participating in the Olympiads in Informatics — from beginners to participants of international competitions. SIS is held in July and August, each of them is visited by about 200 students from all over Russia and abroad. The language of the camp is Russian. Additional information about SIS is posted at [lksh.ru](http://lksh.ru)_ Right now, the August branch of the Summer Computer School is running, and on August 11 the traditional team Olympiad is going to place. I am happy to present a rated round based on it! The round will be rated for both divisions, will be held in [contest_time: 1020], in each division there will be 5 tasks and 2 hours to solve them. The problems of this round and the SIS olympiad were authored and prepared by SIS's teachers: [user:izban,2018-08-09], [user:achulkov2,2018-08-09], [user:Schemtschik,2018-08-09], [us...

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Grakn Forces 2020 [Div1 and Div2] Привет, Codeforces! <center> <img alt="grakn" src="https://grakn.ai/assets/svg/logo.svg" style="float:right; height: 50px; margin: 10px; max-width:10%;"/> </center> Я рад пригласить вас поучаствовать в [contest:1408], который состоится [contest_time:1408]. Он будет **рейнтинговым и открытым для обоих дивизионов**. Этот раунд проводится по инициативе и поддержке компании Grakn Labs. Больше информации можно найти [здесь](https://codeforces.com/blog/entry/82787). Все задачи были придуманы и подготовлены [user:300iq,2020-09-29] и [user:isaf27,2020-09-29]. Большое спасибо [user:growup974,2020-09-29], [user:postscript,2020-09-29], [user:QAQAutoMaton,2020-09-29], [user:PM11,2020-09-29], [user:morzer,2020-09-29], [user:qlf9,2020-09-29], [user:RedDreamer,2020-09-29], [user:gdb_18,2020-09-29], [user:talibmohd,2020-09-29], [user:Dragnoid99,2020-09-29], [user:KAN,2020-09-29] и [user:VladGanzha,2020-09-29] за тестирование раунда и отличные советы, а так же [user:MikeMirzayanov,2020-...

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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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Codeforces Round #162  Привет! Я белочка Лисска. Я буду главным действующим героем сегодняшнего соревнования. Авторами соревнования являются [user:snuke,2013-01-20], [user:hogloid,2013-01-20], [user:DEGwer,2013-01-20], и [user:rng_58,2013-01-20]. Я хочу поблагодарить [user:Gerald,2013-01-20] за помощь в подготовке соревнования, [user:Delinur,2013-01-20] за перевод условий, и [user:MikeMirzayanov,2013-01-20] за платформу Codeforces. Распределение баллов по задачам будет стандартным: 500-1000-1500-2000-2500, в обоих дивизионах. Я столкнусь с множеством трудностей, связанных с камнями, орешками и последовательностями... Пожалуйста, помогите мне! Так как 19:30 MSK очень позднее время для нас (речь идет о времени в Японии), раунд будет перенесен на 17:00 MSK. Вы можете посмотреть время начала соревнования для Вашего часового пояса на timeanddate.com: http://timeanddate.com/worldclock/fixedtime.html?iso=20130120T22&p1=248&ah=2 UPD: Опубликова...

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Codeforces Round #747 (Div. 2) Γεια σου (Hello), Codeforces! [user:Dremix10,2021-10-01] and I are glad to invite you to the first **Cypriot round** [Codeforces Round #747 (Div. 2)](https://codeforces.com/contest/1594) which will take place on [contest_time:1594]. **Note the unusual start time of the round**. As usual, **this round will be rated for participants with rating lower than 2100.** Problems were created and prepared by [user:Dremix10,2021-10-01] and me. We tried to make them interesting, with short and clear statements. We hope that you will enjoy them! I would like to thank: - [user:adedalic,2021-10-01] for amazing coordination of this round. - [user:Dremix10,2021-10-01] for giving the first feedback about every problem I created. - [user:Markadiusz,2021-10-01], [user:cfalas,2021-10-01], [user:m371,2021-10-01], [user:ijxjdjd,2021-10-06], [user:YouKn0wWho,2021-10-06], [user:PurpleCrayon,2021-10-06], [user:flamestorm,2021-10-06], [user:Shinchan01,2021-10-06], [user:rgnerdplayer,2021-...

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Changes in Codeforces problem style over 2020 Sorry for my poor English. I am talking only from Div2 perspective as I think Div1 contest are still ok from this point of view. During 2020 codeforces moved from having problems with variation over known algorithms and data structures to constructive heavy contests. I am not saying that having constructive problems are bad but their amount is way too high and I guess most of us will agree that now a days problems on topics like binary search, DP, Graphs or segment tree or other data structures etc are almost extinct in Div2 rounds. Lets take last Div2 [contest:1474] as an example someone who knows programming language and basic number theory could solve problems till E and can get 1st rank. So in theory someone could become a master or International Master with just number theory and programming language knowledge. I used to like constructive problems a lot (Actually one of my stronger topics) but now a days there are just so much constructive problems that they ...

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Codeforces Round #320 [Bayan Thanks-Round] Hello, everyone! Codeforces Round #320 will be held at [Sep/16/2015 18:00 MSK](http://timeanddate.com/worldclock/fixedtime.html?day=16&month=9&year=2015&hour=18&min=0&sec=0&p1=166). Note that round **starts in the unusual time**! The problems are from [user:tmt514,2015-09-15], [user:shik,2015-09-15], [user:drazil,2015-09-15], and me([user:dreamoon,2015-09-15]). Also we want to thank [user:Zlobober,2015-09-15] for helping us preparing the round, [user:AlexFetisov,2015-09-15] and [user:winger,2015-09-15] for testing this round , [user:delinur,2015-09-15] for translating the statement into Russian, and [user:MikeMirzayanov,2015-09-15] for Codeforces and Polygon. This is my second time organizing a problemset for a Codeforces round (my previous round: [#292](http://codeforces.com/blog/entry/16446)). In my previous round all problems were provided by me. But I think that if problems are provided by more people, then the contest will be more interesting! So I asked my friends to help ...

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Codeforces Round #228 Hello everyone! [Codeforces Round #228](http://codeforces.com/contests/388,389) (Div. 1 and Div.2) will start at [Monday, 3 February 2014, 19:30:00 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?day=3&month=2&year=2014&hour=19&min=30&sec=0&p1=166). This is my 2nd round on Codeforces. (Click [here](http://codeforces.com/blog/entry/8163) to see my last round) , As usual, there will be 7 problems: 2 for Div2, 2 for Div1 and 3 for both. And same with the last round, the main character of all problem will be Fox Ciel. I would like to thank [user:Gerald,2014-02-01] for testing, and [user:MikeMirzayanov,2014-02-01] for the Codeforces project including [polygon](http://polygon.codeforces.com) system. Good luck and have fun! The score distribution will be published later. And the editorial will be published right after the system test. By the way, yesterday is the Chinese new year. So I'd like to say Happy New Year to everyone who celebrate it! And I'm very glad ...

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SWERC 2022-2023 <img src="/predownloaded/70/37/703737cf76db63e4b7bbb9fd63a01a3dc446371e.png" style="width:250px; float:right; margin: 0 1em 1em 1em"/> The Southwestern Europe Regional Contest will take place on the 19th of February in Milan. It is the ICPC regional contest (i.e., the winning teams will advance to the ICPC World Finals) for teams from France, Israel, Italy, Portugal, Spain, and Switzerland. The mirror contest [contest:1776] will be held on Codeforces at [contest_time:1776] and will last 5 hours. The mirror contest will contain the problems from the official competition plus some additional problems. I am the chief judge for the competition and I want to thank: - The amazing set of judges who proposed and prepared the problems: [user:cescmentation_folch,2023-01-24], [user:cip999,2023-01-24] (vice chief judge), [user:gangsterveggies,2023-01-24], [user:giove,2023-01-24], [user:gog.gerard,2023-01-24], [user:jinlifu1999,2023-01-24], [user:Petr,2023-01-24], [user:Simon,2023...

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Ultimate guide to TopCoder plugins Hi, I wanted to present to you guide on how you should set up TopCoder Arena in order to make competing in TC much more pleasant experience. Or at least guide how to do the same thing as I did which seem very comfortable to me compared to this big pain of competing in bare default Arena. In case you want to grab easy upvotes please leave here some joke about how I am jealous about ~Radewoosh,2018-08-16 getting insane boost in his contribution by writing his blogs, but the real reason is that I screwed my setup recently and needed to go through this painful and magical setup once again and it seems this information is very nontrivial and not available publicly in a known place (which I believe is one of reasons TopCoder is losing its popularity, but I hope thanks to this post I can give slight boost to it by settling up Arena problems once and for all for many people), so I wanted to share it with others. I want to express my sincere thanks to [user:tomasz.kociumaka,2018-08-16] for guid...

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Codeforces Round #493 Hi, codeforces! I am happy to invite you to the codeforces round #493, which happens at [contest_time:997]. This round writers are &mdash; Ildar [user:300iq,2018-06-30] Gainullin, Grigory [user:gritukan,2018-06-30] Reznikov, Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov, and me, [user:_kun_,2018-06-30]. Big thanks for people, who tested round &mdash; Shiqing [user:cyand1317,2015-05-01] Lyu, Andrew <a class="rated-user user-green" href="/profile/GreenGrape" title="Finally Green GreenGrape">GreenGrape</a> Rayskiy, Ivan [user:isaf27,2018-06-30] Safonov, Alexey [user:aleks5d,2018-06-30] Upirvitsky. Also thanks to Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov and Nikolay [user:KAN,2018-06-30] Kalinin for help with round preparation. And to Mike [user:MikeMirzayanov,2018-06-30] Mirzayanov for codeforces and polygon systems. Traditionally, there will be 5 problems for 2 hours. I hope you will enjoy the problemset, good luck and have fun! Scoring distribution will be pu...

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Lyft Level 5 Challenge 2018 — Final Round <a href="https://www.lyft.com/level5/" style="width:150px;float:right;margin:0 1em 1em 1em;"><img src="https://assets.codeforces.com/images/lyft-logo.png"/></a> Hi, I am happy to announce that [Lyft Level 5 Challenge 2018 &mdash; Final Round](https://codeforces.com/contests/1044,1074,1075) will be held in Palo Alto on [contest_time:1044]. The official round contains **six** problems and will last for **two** hours. Winners will receive: - First place: $2000 - Second place: $1000 - Third place: $500 Here is the list of onsite finalists: <table border="1" cellpadding="5" cellspacing="5" cellspacing="5" cellspacing="5"> <tr> <td> [user:tourist,2018-11-02] </td> <td> [user:LHiC,2018-11-02] </td> <td> [user:scott_wu,2018-11-02] </td> <td> [user:ksun48,2018-11-02] </td> <td> [user:Marcin_smu,2018-11-02] </td> </td> <tr> <td> [user:matthew99,2018-11-02] </td> <td> [user:ecnerwala,2018-11-02] </td> <td> [user:Kostroma,2018-11-02] </td> <td> [user:RomaWhite...

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Good Bye 2016 — hints and codes You can download my codes to all problems [here](http://www.filedropper.com/codes_1). I will write a full editorial in the next few days. Now you can read hints and short solutions. [problem:750B] <spoiler summary="hint"> Create a variable that will denote your current distance from the North Pole. What are allowed values of this variable? When can't we go West or East? </spoiler> [problem:750C] <spoiler summary="hint1"> Let $x$ denote the initial rating (or his final rating, whatever is easier for you to think about). The information that Limak is in some division in the $i$-th contest gives us some inequality for $x$. Can you see it? </spoiler> <spoiler summary="hint2"> For every contest we know that the current rating is $x$ increased by some prefix sum of c_i (changes of rating). If Limak is in the division 1, we have inequality x+prefSum >= 1900 so we have x >= 1900-prefSum. If Limak is in the division 2, we have inequality x_prefSum <= 1899 so it is ...

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Codeforces Round #339 (Div. 1 & Div. 2) Hi all! In two days, at 19:35 MSK Codeforces Round #339 (Div. 1 & Div. 2) will take place. This is an unusual round since we — the problemsetters — are highschool students who participate in the programming training group at high school #179. This round is our first effort and we did our best to make it interesting and bug-free. I invite you all to compete in this round since the problems will be **solvable**, but even [user:tourist,2016-01-13] will have to think over some of them. :) With supervision and control from Mikhail Tikhomirov ([user:endagorion,2016-01-13]), the problems were developed by: Egor Chunaev ([user:ch_egor,2016-01-13]), Vasily Alferov ([user:platypus179,2016-01-13]), Dmitry Sayutin ([user:cdkrot,2016-01-13]), Timofey Gutor ([user:Tigutor,2016-01-13]), Maria Fedorkina ([user:MF2000,2016-01-13]). Mikhail Sorokin ([user:themikemikovi4,2016-01-13]) and Sergey Aleikin ([user:Derrior,2016-01-13]) contributed their problem ideas. We thank Gleb Evstropov ([user:Gl...

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CodeCraft-17 and Codeforces Round #391 (Div. 1 + Div. 2, combined) Announcement Hello Everyone! I would like to invite you to CodeCraft-17, which will take place on [Thursday 12th January 2017, 9:05PM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CodeCraft-17&iso=20170112T1535&p1=1440&ah=3). The round will be a Div1 + Div2 combined round and is **rated**. [Felicity, IIIT Hyderabad](https://www.facebook.com/felicity.iiith) presents [Threads ‘17](https://felicity.iiit.ac.in/threads/), the magnificent annual technical fest, is finally here in its 13th edition! With a plethora of intellectually engaging online contests in various fields of programming, mathematics and general knowledge, Threads is a celebration of the spirit of computing and engineering. The grand algorithmic sprint called **CodeCraft**, parallel programming in **Kernel Cruise**, mathematical enigmas in **Gordian Knot**, jeopardy style CTF event called **Break In**, overall Threads '17 has something to offer for every kind of computing enthusiast! ![Codecraft Poster ](...

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Codeforces Round #604 (div1 & div2) Hello everyone! I am glad to invite you to [Codeforces Round #604](https://codeforces.com/contests/1264,1265), which will take place on [contest_time:1264]. The round will be rated for both divisions. Exactly 300 Codeforces rounds passed since my first one (Round 304). I have learned a lot of things here and have much fun in participating in the competitions. Now, I want to contribute to this community by proposing some problems. I hope that you will find something interesting in solving them. The contest is prepared by me, [user:laoriu,2019-12-04], [user:I_love_Hoang_Yen,2019-12-04], coordinator [user:isaf27,2019-12-04] and CF admin [user:MikeMirzayanov,2019-12-04]. As usually, we must specially thank to below people who make contest possible: - [user:MikeMirzayanov,2019-12-04] for the powerful Polygon and Codeforces system. - [user:isaf27,2019-12-04] for coordinating the round. - [user:Um_nik,2019-12-04], [user:arsijo,2019-12-04], [user:opukittpceno_hhr,2019-12-04], ...

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Technocup 2022 — Elimination Round 2 and Codeforces Round #755 (Div. 1, Div. 2) Hi all! This weekend, at [contest_time:1584] we will hold [contest:1588] and [contest:1589]. They are based on problems of Technocup 2022 Elimination Round 2 that will be held at the same time. Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at <a href="https://technocup.mail.ru/">Technocup website</a> and take part in the Elimination Round. Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests! - The round authors are: [user:Denisson,2021-11-13], [user:antonis.white,2021-11-13], [user:dimatimoshin23,2021-11-13], [user:__JustMe__,2021-11-13], [user:4qqqq,2021-11-13], [user:Aleks5d,2021-11-13] - Coordinator: [user:isaf27,2021-11-13] - Thanks [user:KAN,2021-11-13] for help with round preparation, also thanks [user:MikeMirzayanov,2021-11-13] for the great Codeforces and Polygon systems. - Thanks [user:221,2021-11-13], [user:Makcum888,2021-11-13], [user:Melonad...

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

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Codeforces Round #681 [Div1 и Div2] Важный день! Сегодня мы узнаем победителей трека Engine VK Cup 2019–2020. Лучшие участники сезона, прошедшие отбор в феврале, к сожалению, не соберутся вместе на Новой сцене Александринского театра в Санкт-Петербурге, но в 17:05 начнут бороться за [звание чемпиона VK Cup](https://assets.codeforces.com/files/vkcup-2019-preresults.html) и призовой фонд: - 1 место — 524 288 рублей, - 2 местo — 131 072 рубля, - 3 местo — 32 768 рублей. Болеть за финалистов можно по [ссылке](https://assets.codeforces.com/files/vkcup-2019-preresults.html). А уже в [contest_time:1442] вас ждут Div1 и Div2 раунды по мотивам задач финала VK Cup. Задачи для финального раунда VK Cup подготовлены сотрудниками ВКонтакте [user:PavelKunyavskiy,2020-11-01], [user:izban,2020-11-01], [user:YakutovDmitriy,2020-11-01] и [user:Kurpilyansky,2020-11-01], [user:.tx,2020-11-01], а также неповторимым [user:300iq,2020-11-01]. Дополнительные задачи для Codeforces раунда подготовлены [user:Supermagzzz,2020-11-01],...

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Codeforces Round #290 Editorial **Update 1** : here are the reference solutions for this contest: 1. Div2-A: [http://ideone.com/JP1Ksj](http://ideone.com/JP1Ksj) 1. DIv2-B: [http://ideone.com/udz3bN](http://ideone.com/udz3bN) 1. Div2-C / Div1-A: [http://ideone.com/KVobNb](http://ideone.com/KVobNb) 1. Div2-D / Div1-B: [http://ideone.com/7MQqOm](http://ideone.com/7MQqOm) 1. Div2-E / Div1-C: [http://ideone.com/z3FsU2](http://ideone.com/z3FsU2) 1. Div1-D: [http://ideone.com/Y7j21a](http://ideone.com/Y7j21a) 1. Div1-E: [http://ideone.com/Orbacp](http://ideone.com/Orbacp) Note that for Div2-E / Div1-C, it is for the harder version: we need to handle '1' in the cycle. [problem:510A] There are 2 different ways to solve this kind of task: First one is to simulate the movement of the snake head, and you draw '#'s on the board. The code will look like: ~~~~~ head = (1, 1) repeat: repeat m-1 times: head move to right repeat 2 times: head move down repeat 2 times: head move down repeat m-1 ti...

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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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Way of problemsetter *The mystery of creating rounds unveiled by author of the 4 of them! The guide for preparing the round without horror-fiction and pastorals!* Thanks for [user:RodionGork,2014-06-13], who push me to writing this post and thanks for [user:lucAbalo,2014-06-13], who push [user:RodionGork,2014-06-13] to pushing me to writing this post. Also, many thanks to [user:RodionGork,2014-06-13] for the translation of this post to English. ##1. Inventing problems It's hard to advise anything on this point. There's no some standard way of creating problems &mdash; and if one have existed we'll have only "complicated algorithmic exercises" instead of "problems". People who participated in Russian Code Cup do know well the tasks of that sort. To cook good and interesting problem there should be some **idea!** which came to your mind (and later to minds of participants of the contest). Even the simplest problems of `A` level for the `Div2` should have some **idea**. So here is the war...

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[Tutorial] A Way to Practice Competitive Programming : From rating 1000 to 2000 Dear Codeforces Community.<br /> <br /> Today I want to share some ways to practice competitive programming and getting rating. I think this is helpful for those who is practicing competitive programming hardly but rating is sluggish. (By the way, on July 17th, I have a project of competitive programming said CombNaf in Japan. I did a lecture about this. Great thanks to the CombNaf's organizer is [user:Nafmo2,2017-07-17].)<br /> <br /> I will write this by **4 steps**: rating **<font color="grey">1000</font> --> <font color="green">1250</font>**, **<font color="green">1250</font> --> <font color="aqua">1500</font>**, **<font color="aqua">1500</font> --> <font color="blue">1750</font>**, **<font color="blue">1750</font> --> <font color="purple">2000</font>**, in Codeforces Rating System.<br /> <br /> Before writing about each step, I wrote it as premise: You don't have to do this way. This is just a way to practice. Ways to practice is different among people, so I think this may n...

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VK Cup Round 2 + Codeforces Round 409 Announcement Hello! The round 2 of VK Cup 2017 will take place on April 16 at 18:35 MSK (check your timezone [here](http://timeanddate.com/worldclock/fixedtime.html?day=16&month=4&year=2017&hour=18&min=35&sec=0&p1=166)), along with separate div1 and div2 Codeforces Round #409. The contest "VK Cup 2017 — Round 2" is for teams qualified from round 1. The top 100 teams will advance to the Round 3, while other ones will have one more chance in the Wild Card Round 2 later this month. Those who don't participate in the VK Cup can take part in the Codeforces Round #409 individually (problems will be available in English too). All three rounds last 2 hours, and all are rated. The round would not be possible without the following people (in no particular order): [user:KAN,2017-04-14], [user:Errichto,2017-04-14], [user:winger,2017-04-14], [user:AlexFetisov,2017-04-14], [user:LiChenKoh,2017-04-14], [user:xiaowuc1,2017-04-14], [user:MikeMirzayanov,2017-04-14]. Additionally, I thank VK company for sponso...

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Codeforces Round #641 Editorial You can view Chinese editorial here: https://www.luogu.com.cn/blog/Caro23333/codeforces-round-641-zhong-wen-ti-xie Div2.A Problem and editorial by [user:ProgSlacking,2020-05-12] <spoiler summary="Editorial"> [tutorial:1350A] </spoiler> <spoiler summary="Code"> ~~~~~ #include <iostream> #include <cstdio> #include <cstring> #include <cstdlib> #include <algorithm> using namespace std; int main() { int T; cin >> T; while(T--) { int n,k; cin >> n >> k; if(n%2==0) { cout << n+2*k << endl; continue; } int p = 0; for(int i = n; i>=2; i--) if(n%i==0) p = i; cout << n+p+2*(k-1) << endl; } return 0; } ~~~~~ </spoiler> Div2.B Problem and editorial by [user:ProgSlacking,2020-05-12] <spoiler summary="Editorial"> [tutorial:1350B] </spoiler> <spoiler summary="Code"> ~~~~~ #include <iostream> #include <cstdlib> #include <cstdio> #include <cstring> #include <algorithm> using namespace std; con...

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An editorial of Topcoder SRM 672 Hi everybody! It was my first experience of writing problems for TopCoder SRM, hope you liked it. I was a writer of Easy and Medium task in both divisions, [user:subscriber,2015-10-21] was an author of both Hard tasks. In div1 they were harder than usual, but I hope you still liked them. #### Div2 easy This task was just about implementing exactly what is described in the statement. Looks like Python has a built-in support of set comparison. Usually coders using Python have a disadvantage, but in this task it looks more like an advantage :) There are built-in functions for sets in C++ and Java too, I recommend to learn about them even if you successfully submitted this problem. #### Div2 medium Knowing strings a and b, we can build a reverse mapping $q[d] = c$, that maps the encoded letter $d$ to it's original corresponding letter $c$. For letters that do not appear in $b$, we remember that we don't know their pre-image. After that, we just apply our mapping $q$ to a string...

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Forethought Future Cup — Final Round Hello again Codeforces! The Forethought Future Cup Final round will start on [May 4th, 10:05am PDT](https://www.timeanddate.com/worldclock/fixedtime.html?day=4&month=5&year=2019&hour=20&min=5&sec=0&p1=166). **This round will be rated for everyone**. There will be three separate rounds, one for onsite contestants, one for div1, and one for div2. Onsite and div1 will have the same problems. Each round will have 6 problems and be 2 hours long. Here is a table of the onsite contestants. |---| | [user:scott_wu,2019-05-01] | [user:neal,2019-05-01] | [user:ACRush,2019-05-01] | [user:Fdg,2019-05-01] | [user:Ra16bit,2019-05-01] | | [user:Kenny_HORROR,2019-05-01] | [user:liymbear,2019-05-01] | [user:ll931110,2019-05-01] | [user:xiaowuc1,2019-05-01] | [user:Suzukaze,2019-05-01] | | [user:yzyz,2019-05-01] | [user:stevenkplus,2019-05-01] | [user:pmnox,2019-05-01] | [user:OpalDshawn,2019-05-01] | [user:NEU20133823,2019-05-01] | | [user:tap_tapii,2019-05-01] | [user:Svlad_Cjelli,2019-05-...

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On Div2ABs 2 years ago, [user:antontrygubO_o,2022-04-27] wrote [a blog](https://codeforces.com/blog/entry/75163) about div2ABs where he expressed his opinions that d2ABs should not be about "here is a statement, please implement what is written there". Thanks to him, the quality of d2ABs (and problem quality in general) have certainly improved. However, I still believe that there still quite large differences between how coordinators/problemsetters view d2ABs and how the intended participants view them. From the survey made by [user:kpw29,2022-04-27], we can see that most people agree that most people agree that we should **primarily** consider the target audience when proposing a task. I too think if a task is boring to div 1 contestants, we should not think of that as a reason to immediately disqualify a problem from being a d2A.  I think when people judge the interesting-ness of d2As, they try...

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Codeforces blocking my account for a fake cheating accuse Requested to publish from [user:Basilhijaz,2023-10-09]: " Hello, I am [user:Basilhijaz,2023-10-09]. I participated in lots of Codeforces rounds and the last one I did was [contest:1879]. Unfortunately, I was trying to login to my account today and got the message "User is disabled by administrators". I checked my email and it looks like I was accused of cheating in that specific round. Apparently my Submission on Problem B [submission:224888371] is so close to [user:LetsPractice,2023-10-09]'s Submission [submission:224901176]. This problem we both got accused of copying from each other is B in an Educational round which means solutions can get actually really close and if you notice the solutions are so short which increases the probability of matching. Previous Accuses of Cheating Attempts (Problem, My Submission, Similar Submission/s)(problem classification): - ([problem:1462D], [submission:101301240], [submission:101299306]) (D div3). - ([problem:1670A], [submi...

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Virtual participation is great! I want to promote the option of virtual participation in contests, since I noticed it's not used as often as it could be. Perhaps it's just not something people keep in mind, but I'm sure that if you use it often, it will help you a lot. What does it do? It allows you to compete in past contests as if you were actually competing when the contest took place &mdash; there are only two differences: - it's unrated - there are no hacks and so far, no pretests Virtual participation is a great way to compete without worrying about your rating. Instead of making a fake account that you then throw away, you can just participate with your real account with no risk. If you care about embarassing yourself with poor performance, don't worry about it. Nobody cares. Virtual participation is also a great way to train. Unlike regular upsolving, you have a timer, so you can't just take your time trying stupid shit or overthinking. This way, it's much better for training fast thinking. Takin...

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Проект для помощи и улучшения Codeforces: "Обсуждаем задачи" **Введение** Здравствуйте! Мы любим Codeforces и хотим, чтобы там были классные контесты и как можно больше людей получали удовольствие от участия. Поэтому мы решили создать проект, который называется «Обсуждаем задачи». Мы не связаны напрямую с администрацией Codeforces, однако у нас есть поддержка и одобрение от [user:MikeMirzayanov,2019-02-09], и мы очень надеемся на содействие его и координаторов контестов. **В чем суть проекта?** Суть проста — вы присылаете нам в Telegrame или VK (ниже указаны адреса) свои задачи в любом количестве с указанием предполагаемой сложности (можно даже одну; нужно только, чтобы была хотя бы одна задача уровня не ниже Div2C) . Таким образом, вы передаете интеллектуальные права на задачу нам, и обязуетесь при этом далее не использовать ее ни в каком виде, в том числе в предложениях контестов на Codeforces или иных платформах, а также гарантируете, что она еще нигде не использована и никуда не предложена; далее возможны два варианта. - Мы прини...

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Codeforces Round #824 (Div. 2) Hi, Codeforces! Three years later, first ideas of a contest turned into this complete set of problems, so I am glad to invite you to take part in [Codeforces Round #824 (Div. 2)](https://codeforces.com/contest/1735), which will take place on [contest_time:1735]. The round will be rated for the participants with rating lower than 2100. Participants from the first division are also welcomed to take part out of competition. You will be given <b>2 hours 15 minutes</b> to solve <b>6 problems</b>. All the problems were created and prepared by me. I would also like to thank: <ul> <li> [user:KAN,2022-10-01] for awesome coordination! </li> <li> [user: Aleks5d,2022-10-01], [user: arzhantsev64,2022-10-01], [user: ChthollyNotaSeniorious,2022-10-02], [user: DanWallgun,2022-10-01], [user: flowerletter,2022-10-02], [user: Gegege337,2022-10-01], [user: Imakf,2022-10-02], [user: LeoRiether,2022-10-01], [user: mejiamejia,2022-10-02], [user: okwedook,2022-10-01], [user: PO3OBAR_Bblnb,2022-...

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Codeforces Round #415 Hello everyone! This Saturday [May 20, 21:05 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=20&month=5&year=2017&hour=21&min=05&sec=0&p1=166) rated Codeforces Round #415 takes place. As for our previous round 384, the problems were set by Kiril [user:kefaa,2017-05-16] Gulin and Yura [user:hloya_ygrt,2017-05-16] Shilyaev. And this time Daniil [user:Melnik,2017-05-16] Melnichenko joined us! Many thanks to coordinator Alex [user:netman,2017-05-16] Vistyazh for help in preparations of the round, and also to Mike [user:MikeMirzayanov,2017-05-16] Mirzayanov for Codeforces and Polygon systems. While everyone is waiting for second half of "SKAM" series season, we offer you to solve problems, main characters of which would be stunning girl Noora and well-known to you from [problem:794F] hacker Leha! As always, participants of both divisions will be given 5 problems and 2 hours to solve them. Scoring will be announced before the round. We hope you'll like our round...

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Editorial of SRM #673 Div2 ------------------ [Codes for all Div2 problems](http://ideone.com/FO7ixD) **BearSong (250p.)** There are two ways to solve this problem. The first way is to create an array $T$ of size 1000 to count occurrences of each note. For each number $x$ in the given sequence we should do `T[x]++`. After that, we should iterate over $T$ and count the number of indices with value $1$. There is an alternative $O(N^2)$ solution. For each element of the given sequence we can iterate over other elements to check whether some of them is equal to the current one. **BearSlowlySorts (500p.)** Again, there are two ways to solve a problem. The first one is quite boring. One could notice that the answer must be small and we can simulate first few moves in any possible way. Some extra observation is that after sorting the first N-1 we shouldn't sort them again in the next move. So we should either do moves in the order {first, last, first, last, ...} or {last, first, last, fir...

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Feature Request: Consolidating Different Versions of the Same Problem First of all, Codeforces is great and I like its UI much better than other platforms. But there is one issue that annoys me repeatedly. I haven't seen it discussed in a blog yet (apologies if I missed it), so I thought I'd make this request. Sometimes I revisit a problem I solved before, and I want to see my submission. Then I get confused because I don't see my submission in the lower right corner of the problem page. Eventually, I find that I need to view a different link that shows the same problem. Now, it makes some sense that the same problem should have different links. For example, if I'm viewing the problem in a virtual contest, I want to see the correct short-name depending on the division. If the problem is div2C, I want to see C if I got there from div2, or A if from div1. Another example is that if a problem came from the contest, I don't want to see tags, but I might if I got there from the problemset. So, a problem can have multiple links. For example, all these...

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Codeforces Round #385 Hello everyone! Codeforces round #385 will take place at the unusual usual time of [Saturday, 17 December 19:35 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+385&iso=20161217T1935&p1=166&ah=2). Thanks to the following people for making this round possible. - [user:LiChenKoh,2016-12-16], [user:xiaowuc1,2016-12-16] for helping develop problems and discussing ideas with me. - [user:winger,2016-12-16], [user:AlexFetisov,2016-12-16] for testing the problems - [user:GlebsHP,2016-12-16] for all his valuable help with the round. - [user:MikeMirzayanov,2016-12-16] for the great Codeforces and Polygon platforms. As usual, contestants will have 2 hours to solve 5 problems. Hope you will enjoy the problems! Scoring will be announced closer before the round. **EDIT:** It may be helpful to read the [Interactive Problem Guide](http://codeforces.com/blog/entry/45307) before the round for both divisions. **EDIT 2:** The scoring distribution wil...

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Технокубок 2020: Финальный раунд и Codeforces Round #625 Всем привет! <a href="//codeforces.com/technocup2020" style="float: right;margin: 0 0 1.0em 1.0em;"><img src="//assets.codeforces.com/images/technocup-narrow-logo.png" style="max-width: 100.0%;max-height: 100.0%;"></a> Сегодня, 1 марта 2020 года пройдет финальный раунд олимпиады для школьников Технокубок! Участники, которые стали лучшими на четырех отборочных раундах, сегодня поборются за первые места на онсайте. Финальный раунд стартует в 13:00 по московскому времени. Для тех, кто хочет посоревноваться на тех же задачах, будет проведено два обычных раунда Codeforces: один для первого, другой для второго дивизиона. Раунды начнутся в 16:05 по московскому времени, не пропустите! Раунд будет проведен сразу после окончания официального онсайн-раунда. По этой причине раунд может быть слегка перенесен вперед, если расписание старта онсайта будет изменено. Конечно, если вы участвуете в финальном раунде Технокубка, то вы не можете участвовать в раунде вечером. Задачи раунда гото...

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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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Invitation to CodeChef SnackDown Elimination and Parallel Rated Contests We are very glad to invite you to participate in [SnackDown Elimination round](https://www.codechef.com/SNCKEL21)! It will be **rated** for all participants. 60 participants will qualify for the finals from the Elimination round. They include: <ul> <li>The top 25 participants from the Elimination round.</li> <br> <li>Additional top 2 school participants </li> <br> <li>Additional top 2 female participants </li> <br> <li>Additional 31 Indian participants, including: <ul> <li> 10 top Indian participants </li> <br> <li> The next 15 Indian participants from the Elimination Round qualify provided they solve at least 2 problems. </li> <br> <li> 3 top Indian School participants</li> <br> <li> 3 top Indian Female participants </li> </ul> </li> </ul> Those, who haven't advanced, are invited to participate in the [Parallel rounds](https://www.codechef.com/SDELP21), which will be held for all divisions. All three rounds are **rated** too. [Time: 7:30 PM ...

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Codeforces Beta Round #99 <p>Привет.<br /><br />Сегодняшний раунд подготовил я. Меня зовут Михаил Тихомиров, я студент 4 курса мехмата МГУ, помимо этого работаю в Яндексе разработчиком-исследователем.<br /><br />Хочется сказать спасибо Артему Рахову ([[user:RAD,2011-12-24]]) за значительную помощь и грамотную координацию, Марии Беловой ([[user:Delinur,2011-12-24]]) за традиционно качественный перевод условий, а также [[user:MikeMirzayanov,2011-12-24]] за то, что все мы здесь сегодня собрались. =)</p><p>Раунд будет для обоих дивизионов. В каждом дивизионе, как и всегда, будет по пять задач, некоторые из которых будут общими, но не все.</p><p>Разбалловка:</p><p><b>Div1: 500-1000-2000-2000-2500.</b></p><p><b>Div2: 500-1000-1500-2000-3000.</b><br /></p><p>Сегодняшний раунд - последний в 2011 году. Я хочу поблагодарить команду Codeforces, всех, кто придумывал, готовил или помогал готовить задачи в этом или прошлых годах, а также тех, кто способствует развитию проекта. Codeforces давно перестал быть просто платформой...

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Codeforces Round #395 (Div. 1 + Div. 2) Ladies and gentlemen! Codeforces Round #395 for both divisions will happen tomorrow, on [Thursday, 2 February 2017 at 13:35 UTC](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23395&iso=20170202T1335&p1=1440). Problems were prepared by me (Vasiliy Alferov) and students of Moscow school #179: [user:s17b2_voroneckij,2017-02-01] (Dima Voronetsky), [user:ilya_the_lamer,2017-02-01] (Ilya Pauzner) and [user:akvasha,2017-02-01] (Anton Kvasha). Also, [user:KAN,2017-02-01] (Nikolay Kalinin) is author of one of the problems. Invaluable help was given to us by Codeforces coordinator [user:KAN,2017-02-01] (Nikolay Kalinin). Thanks to [user:MikeMirzayanov,2017-02-01] (Mike Mirzayanov) for wonderful platforms Codeforces and Polygon. Also thanks to [user:Endagorion,2017-02-01] (Mikhail Tikhomirov), [user:winger,2017-02-01] (Vladislav Isenbaev), [user:AlexFetisov,2017-02-01] (Alex Fetisov) and [user:cdkrot,2017-02-01] (Dmitry Sayutin) for reading out our statement...

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Codeforces Round 917 (Div. 2) Hi, Codeforces! I'm glad to invite you to take part in [Codeforces Round 917](https://codeforces.com/contests/1917), which will take place on [contest_time:1917]. **Round will be rated for participants with rating less than $2100$.** Participants from the first division can take part out of competition. There will be $6$ problems for $2$ hours. The problems are authored by [user:igori,2023-12-24], [user:zidder,2023-12-24] and me. **Part of the problems in this round were in the Yerevan SU 28.1₀.₂₀₂3 Contest. If you participated in it or know at least one problem from it, please refrain from participating in this round.** We would like to thank - Thanks to [user:thescrasse,2023-12-22] for excellent round coordination; - Thanks to our testers: [user:KAN,2023-12-22], [user:S_Voloch,2023-12-22], [user:Tmitmi,2023-12-22], [user:Pagode_Paiva,2023-12-22], [user:hgglmao,2023-12-22], [user:IceWolf898,2023-12-22], [user:daud04,2023-12-22], [user:dewana310,2023-12-22], [user:menbo...

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Codeforces Round #162 Tutorial #### [Div2 A Colorful Stones (Simplified Edition)](http://codeforces.com/problemset/problem/265/A) (Author: [user:rng_58,2013-01-21]) In this problem you just need to implement what is written in the statement. Make a variable that holds the position of Liss, and simulate the instructions one by one. #### [Div2 B Roadside Trees (Simplified Edition)](http://codeforces.com/problemset/problem/265/B) (Author: [user:snuke,2013-01-21]) The optimal path of Liss is as follows: First she starts from the root of tree 1. Walk up the tree to the top and eat a nut. Walk down to the height $min(h_1, h_2)$. Jump to the tree 2. Walk up the tree to the top and eat a nut. Walk down to the height $min(h_2, h_3)$, $\cdots$ and so on. #### [Div1 A / Div2 C Escape from Stones](http://codeforces.com/problemset/problem/264/A) (Author: [user:DEGwer,2013-01-21]) In this problem, there are many simple algorithms which works in $O(n)$. One of them (which I intended) is following: You should...

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Codeforces Round #737 (Div. 2) Hello, Codeforces! I'm glad to invite you to [Codeforces Round #737 (Div. 2)](https://codeforces.com/contests/1557) , which will be held on [Monday, August 9, 2021 at 16:35 UTC+2](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23737+%28Div.+2%29&iso=20210809T1635&p1=53&ah=2). This round **rated for the participants with rating lower than 2100**. You will be given **5 problems** and **2 hours** to solve them.all problems were prepared by me and [user:AhmedEzzatG,2021-08-04]. One of the problems will be **interactive**. So, it is recommended to read the [guide on interactive problems](https://codeforces.com/blog/entry/45307) before the round. I would like to thank - 1. [user:Aleks5d,2021-08-04], for awesome coordination of our round and suggested one of the problems. 2. [user:Kaneki-kun,2021-08-04] for help us to prepare the problems. [user:compiler_101,2021-08-04] ,[user:Shanks,2021-08-04] ,[user:DeadPillow,2021-08-04] , and [user:Omar_E...

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Codeforces Round #359 Editorial If you notice typos or errors, please send a private message. <br> <br> [Div2A Free Ice Cream](http://codeforces.com/contest/686/problem/A) <br> Author: [user:cdkrot,2016-06-24] <br> Developer: [user:ch_egor,2016-06-23] <br> You just needed to implement the actions described in statement. <br> If you solution failed, then you probably forgot to use 64-bit integers or made some small mistake. <br> Correct solution: <br> <br> <spoiler summary="C++ code"> ~~~~~ #include <iostream> #include <cstdio> #include <cstdlib> #include <string> #include <cstring> #include <vector> #include <stack> #include <queue> #include <deque> #include <set> #include <map> #include <cassert> #include <algorithm> #include <iomanip> #include <ctime> #include <cmath> #include <bitset> #pragma comment(linker, "/STACK:256000000") using namespace std; typedef long long int int64; typedef long double double80; const int INF = (1 << 29) + 5; const int64 LLINF = (1ll <<...

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Codeforces Round #870 (Div. 2) Hi, Codeforces! I am glad to invite you to take part in [Codeforces Round #870 (Div. 2)](https://codeforces.com/contest/1826), which will take place on [contest_time:1826]. The round will be **rated for the participants with rating lower than 2100**. Participants from the first division are also welcomed to take part out of competition. You will be given **2 hours** to solve **6 problems**. All the problems were authored and prepared by me. One of the problems is interactive, please read [the guide of interactive problems](https://codeforces.com/blog/entry/45307) before the contest. I would also like to thank: <ul> <li> [user:Akulyat,2023-05-04] for excellent coordination and help improving the problems! </li> <li> [user:arzhantsev64,2023-05-04], [user:InversionSpaces,2023-05-04], [user:Aleks5d,2023-05-04], [user:PO3OBAR_Bblnb,2023-05-04], [user:DanWallgun,2023-05-04], [user:Dominater069,2023-05-04], [user:AlperenT,2023-05-04], [user:Sert,2023-05-04], [user:sdl,2023-05-04...

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Problems that I authored so far Hi everyone, after [contest:1854], maybe it's time to collect all my problems here. For now, I've mainly invented easy-ish problems. I wish to invent a very hard problem sooner or later :) <spoiler summary="Update after Pinely Round 3"> Done :D </spoiler> I'm putting the story of each problem under spoiler, because it may contain parts of the solution. I invented many problems by just trying random setups until I came up with something solvable, but some problems (especially the harder ones, for example [problem:1854D]) may have more interesting stories. Fun facts: - I struggled a lot to find a suitable div2A for [contest:1654]. I proposed a lot of problems that turned out to be unsuitable (for example, because they were too hard), then I used them somewhere else. - While I was writing this blog, I realized that [problem:1849E] is identical to my problem [preoii_allenamento \- Allenamento su ChinaForces](https://training.olinfo.it/#/task/preoii_allenamento/statement),...

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Codeforces Round #931 (Div. 2) Hello, Codeforces! I invite you to participate in [Codeforces Round 931 (Div. 2)](https://codeforces.com/contest/1934), which will be held on [contest_time:1934]. The round will be **rated** for participants with **rating lower than 2100**. Participants with higher rating can participate in round unofficially. You will have 2 hours to solve 5 problems, with one of the problems having 2 versions. **One or more interactive problems may occur in the round**, so please read [guide for interactive problems](https://codeforces.com/blog/entry/45307) before the contest. All problems are authored by me. I would like to thank: - [user:Akulyat,2024-02-28] for round coordination and help with preparation - [user:A_G,2024-02-28], [user:okwedook,2024-02-28], [user:rui_er,2024-02-28], [user:jdurie,2024-02-28], [user:lunchbox,2024-02-28], [user:_rey,2024-02-28], [user:wjli,2024-02-28], [user:.-O_O-.,2024-02-28], [user:aryanc403,2024-02-28], [user:akshaykhandelwal,2024-02-28], [us...

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Codeforces Round #562 Hi! I'm glad to invite you to take part in [contest:1168] and [contest:1169], they will be held in [contest_time:1168]. The round will be rated for both divisions (^人^). Participants in each division will be offered five problems and two hours to solve them. The problems were written and prepared by me. Thanks to [user:KAN,2019-05-24] for his help with the round, to [user:sunset,2019-05-24], [user:TLE,2019-05-25], [user:Sooke,2019-05-25], [user:isaf27,2019-05-24], [user:Lewin,2019-05-24], [user:Aleks5d,2019-05-24] and [user:wrg0ababd,2019-05-25] for testing and task discussing! Also, thanks to [user:MikeMirzayanov,2019-05-24] for amazing systems Codeforces and Polygon! Congratulations the winners! Div1: 1) [user:Vn_nV,2019-05-27] 2) [user:OnionPringles,2019-05-27] 3) [user:Errichto,2019-05-27] 4) [user:maroonrk,2019-05-27] 5) [user:Um_nik,2019-05-27] Div2: 1) [user:soros666,2019-05-27] 2) [user:lelolas,2019-05-27] 3) [user:ndmitrovic,2019-05...

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Codeforces Round #499 — анонс Приглашаю Вас поучаствовать в **рейтинговом** [Codeforces Round #499](/contests/1010,1011). Дата и время проведения раунда: [contest_time:1010]. В раунде **Div.1** могут участвовать те, рейтинг которых не меньше, чем 1900. Остальные могут участвовать в раунде **Div.2**. Не пропустите этот контест, ведь следующий Codeforces Round (Div.1, Div.2 или Div.3), номер которого начинается с цифры '4', будет через 3501 раунд! Это первое соревнование, предложенное мной. Надеюсь, что оно Вам понравится. На раунде будет по **6 задач** для каждого дивизиона **(4 задачи общие)**. Контест будет длиться **2 часа**. Главная героиня соревнования &mdash; космонавт Наташа, исследователь Марса. Если вы решите все задачи, её полёт пройдёт удачно. Пять задач из контеста придумал я, Владислав Заводник ([user:VladProg,2018-07-24]), задачи Div2.A и Div2.B придумал Михаил Мирзаянов ([user:MikeMirzayanov,2018-07-24]), а задачу Div1.F придумали Ильдар Гайнуллин ([user:300iq,2018-07-24]) и Дмитрий ...

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Codeforces Round #109 Hello everyone. I'm Mikhail Tikhomirov and I'm the author of today round. I want to say big thanks to Gerald Agapov ([user:Gerald,2012-02-24]) and Artem Rakhov ([user:RAD,2012-02-24]) for great help in preparing this contest, and also Maria Belova for translating the statements into English ([user:Delinur,2012-02-24]). Today round is for contestants from both divisions. Each division has five problems, which intersect, as always. Score distributions are also standard (500-1000-1500-2000-2500). In short, it's a usual round. Or not?.. =) Hope that problems will be interesting, tests will be secure, server will be fast, solutions --- (mostly) correct, and the round will be rated. =) Wish you best of luck! Round finished, thank you all for participating! Results: div1: 1. [user:tourist,2012-02-24] 2. [user:peter50216,2012-02-24] 3. [user:Egor,2012-02-24] 4. [user:WJMZBMR,2012-02-24] 5. [user:gchebanov,2012-02-24] 6. [user:kelvin,2012-02-24] 7. [user:shangjingbo,2012...

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NBHEXT — Know Your Rating Few weeks ago there was yet another discussion about "omg why we wait for the rating updates so long!?!?!" in Russian version of CF. [user:MikeMirzayanov,2015-10-30] said that there are several reasons: 1. cheaters are checked manually; 2. rounds are usually held in the evening and Mike spends some time to get home from the University; 3. sometimes his little daughter asks him to play with her and Mike can't refuse of course After [user:meh,2015-10-30], [user:MaximM,2015-10-30] and me read the third reason, we started to think what can be done about it. After a little thinking we came up with a solution that seemed to make contestants and Mike's daughter happy. The solution was a creation of browser extension that maintains rating changes of a current scoreboard whenever you refresh the result page. Something like this:  Luckily, CodeForces provided us with all the tools to make it happen: an API a...

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Editorial Round 1 of Yandex.Algorithm 2018 <spoiler summary="Police Patrol"> First, let's try to find the largest block that two patrols can cover (hint, it's not k). For instance, we can have one patrol cover $1,2,\ldots,k$. and the other cover $2,3,\ldots,k+1$. So, we can split $n$ houses into blocks of length $k+1$. Now, we have to look at what to do with the leftover houses. If there are more than two empty blocks, we need two patrols to cover both blocks. If there is only one empty block, we only need one patrol. Thus, the answer can be computed by the formula in the code below <spoiler summary="code"> ~~~~~ n,k = map(int, raw_input().split()) print (n/(k+1))*2 + min(2, n%(k+1)) ~~~~~ </spoiler> </spoiler> <spoiler summary="Alphabetic Subsequence"> We can check that this is equivalent to counting the number of permutations of $0,1,2,\ldots,9$ that appear in $s$. There are two solutions: <spoiler summary="solution 1"> Just do it. This is O(10! * |s|) ~ 3*10^8. This is fast enough in some languages. ...

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Codeforces Round #402 Hi, Codeforces! [contest:778] and [contest:779] are going to happen on February, 26th, at [08:05 AM UTC](https://www.timeanddate.com/worldclock/fixedtime.html?day=26&month=2&year=2017&hour=11&min=5&sec=0&p1=166). The round will run at the same time with Innopolis University Open, Olympiad in Informatics. Division 1 problems are the same as olympiad problems. Some of Division 2 problems are prepared by [user:MikeMirzayanov,2017-02-25], thanks to him. The problems are developed by [user:MikeMirzayanov,2017-02-25], [user:YakutovDmitriy,2017-02-25], [user:VArtem,2017-02-25], [user:firezi,2017-02-25], [user:burakov28,2017-02-25], [user:pashka,2017-02-25]. We hope you enjoy the problems! **UPD**: <br/> problem scores for div1: 500 — 1000 — 1500 — 2250 — 2250 <br/> problem scores for div2: 500 — 1000 — 1000 — 1500 — 2000 — 2500 **UPD 2**: Congratulations to winners! **Top-10 (Div.1)** 1. [user:bmerry,2017-02-26] 1. [user:ainta,2017-02-26] 1. [user:Marcin_smu,2017-02-2...

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Codeforces Round #542 Hey Codeforces! We’re thrilled to invite you guys to Codeforces Round #542, which is going to take place on [Sunday, February 24, 2019, at 18:35 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?day=24&month=2&year=2019&hour=18&min=35&sec=0&p1=166). There will be a separate round for each division, and they will be rated! Problems were prepared by [user:MikeMirzayanov,2019-02-24], [user:zoomswk,2019-02-23] and me. As the round authors, we would like to thank [user:ksun48,2019-02-23], [user:isaf27,2019-02-23], [user:tuna_salad,2019-02-23], and [user:Um_nik,2019-02-23] for testing the problems; [user:300iq,2019-02-23] and [user:KAN,2019-02-23] for their help and advice in contest preparation; and the invisible [user:MikeMirzayanov,2019-02-23] for the incredible Codeforces and Polygon platforms. Each division will be given 6 tasks and 2 hours to solve them. As per the Codeforces tradition, scoring distributions will be revealed shortly before the round. We wish you th...

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Codeforces Round #618 Hello Codeforces! We are glad to invite you to the upcoming [Codeforces Round #618](/contests/1299,1300), which will start at [contest_time:1299]. Each division will consist of 5 problems and will have 2 hours to solve the problems. There will be an interactive problem in the round. Learn more about them [here](/blog/entry/45307). This round was prepared by [user:Eva,2020-02-06], [user:sorry_marymarine,2020-02-06], [user:baumanec,2020-02-06], [user:danilz1806,2020-02-06], [user:antontrygubO_o,2020-02-06] and [user:nvmdava,2020-02-06]. We would like to thank [user:MetB,2020-02-06], [user:stefdasca,2020-02-06], [user:cfalas,2020-02-06], [user:gamegame,2020-02-06], [user:hugopm,2020-02-06], [user:Redux,2020-02-06], [user:dorijanlendvaj,2020-02-06], [user:imbr92,2020-02-06], [user:once_twice,2020-02-06], [user:300iq,2020-02-06], [user:Rahul,2020-02-06], [user:AryaKnight,2020-02-06], [user:kefaa2,2020-02-06], [user:manish.17,2020-02-06], [user:Um_nik,2020-02-06], [user:mblazev,202...

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Codeforces Round #253 Всем привет! Приглашаю вас принять участие в Codeforces Round #253, который начнется в [четверг 19 июня в 19:30 MSK](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23253&iso=20140619T1930&p1=352). Раунд будет проходить в обоих дивизионах. Это мой первый раунд Codeforces, и я надеюсь, что вам он очень понравится! Большое спасибо [user:Gerald,2014-06-15] за помощь в подготовке раунда. Также хочется поблагодарить [user:MikeMirzayanov,2014-06-15] за создание удобной платформы для проведения соревнований. Также благодарю тестеров этого раунда: [user:antonkov,2014-06-19], [user:Aksenov239,2014-06-19], [user:VArtem,2014-06-19], [user:subscriber,2014-06-19], [user:niyaznigmatul,2014-06-19]. А еще [user:Delinur,2014-06-19] за перевод условий на английский. Не пропустите шанс получить удовольствие от решения интересных задач! **UPD.** Распределение баллов по задачам: Div1: 500-1500-1500-2000-2500 Div2: 500-1000-1500-2500-2500 **UPD2.** Соревнов...

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Invitation to CodeChef December Cook-Off 2020 We invite you to participate in CodeChef’s [December Cook-Off](https://bit.ly/COOK125-Codeforces), this **Monday, 21st December**, from [9:30 PM to 12:00 AM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=December+2020+Cook-Off&iso=20201221T2130&p1=44&ah=2&am=30). <br> **Note the unusual time**. You will be given a total of **9 problems** (7 in Div2, 7 in Div1) to solve in a duration of **2.5 hours**. Joining us on the problem setting panel are: - Setters: Utkarsh [user:Utkarsh.25dec,2020-12-19] Gupta, Jeevan [user:JeevanJyot,2020-12-19] Jyot Singh, Bhavyesh [user:bhvdsi,2020-12-19] Desai, David [user:ki0apa,2020-12-19] Horne, Vitaly [user:Bugman,2020-12-19] Demidenko, Pranav [user:ExplodingFreeze,2020-12-19] Rajagopalan, Andrzej [user:Okrut,2020-12-19] Turko - Tester: Rahul [user:amnesiac_dusk,2020-12-19] Dugar - Statement Verifier: Jakub [user:Xellos,2020-12-19] Safin - Editorialist: Rajarshi [user:RestingRajarshi,2020-12-19] Basu - Video Editor...

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How to Effectively Practice CP + Problem Solving Guide This is a slight tweak of [a practice guide](https://www.reddit.com/r/usaco/comments/pk3tjp/the_ultimate_usaco_practice_method/) I wrote a while ago on USACO reddit since I thought it could be helpful to people here. Some USACO specific sections or extra clutter I left out here that aren't needed for a general audience. This should cover all general cp advice I have so I never have to retype. #Introduction This is a post on how I believe is the best method to practice modern day competitive programming based on my experiences. I assume you already have some knowledge and know simple things like binary search and dfs/bfs, but **read the footnote if you are complete beginner** (never code, solved <50 problems, div2 A/B too difficult, grey or stuck low pupil). First, a quick tl;dr of the practice strategy before a bunch of specifics and explanation: >**In short, mostly you only need to use codeforces (no matter what contest you're training for), find a rating range where you c...

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Codeforces Beta Round #73. Разбор (Div2) <p></p><div style="background-color: transparent; margin-top: 0px; margin-left: 0px; margin-bottom: 0px; margin-right: 0px; "><u><span id="internal-source-marker_0.6422855302225798" style="background-color: transparent; vertical-align: baseline; ">Задача Div2-A. Аккорд.</span><br></u><span style="background-color: transparent; vertical-align: baseline; ">Нужно понять первым делом простую мысль - ноты по сути являются остатками по модулю 12. А значит минорный аккорд имеет вид {x, x+3, x+7} (mod 12), а мажорный - {x, x+4, x+7}.</span><br><span style="background-color: transparent; vertical-align: baseline; "></span><br><span style="background-color: transparent; vertical-align: baseline; ">Считывать ноты удобно как строки, после чего их лучше тут же заменить на соответствующее число от 0 до 11 - их номером. Для обработки надо было перебрать 6 возможных порядков следования нот в аккорде. Для каждого из 6 порядков проверить, является ли аккорд мажорным или минорным, и если так, то сразу вы...

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[GYM Training Contest] KAIST RUN Spring Contest 2019 (XIX Open Cup. GP of Daejeon) **Update 2019/06/12**: Me and [user:MikeMirzayanov,2019-06-11] managed to upload the Div.2 contest into Gym. Huge thanks him for the great system, and also a kind help! However, I decided not to just open it, but to give a training contest. The contest is scheduled in [June 14 Friday, 09:00 UTC.](https://www.timeanddate.com/worldclock/fixedtime.html?day=14&month=6&year=2019&hour=12&min=0&sec=0&p1=166) Even considering some obvious bias from the setter, I'm personally very proud of the Div.2 contest :D I hope you participate and share the same joy with us! (and of course, please don't cheat!) . . . . . . . . **Update 2019/06/05**: I managed to upload the Div.1 contest into Gym. Have fun! [https://codeforces.com/gym/102201](https://codeforces.com/gym/102201) Open Cup GP of Daejeon is scheduled at [2019/05/05 Sunday, 11:00 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=GP+of+Daejeon&iso=20190505T17&p1=3999&ah=5). Daejeon is a city whe...

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Codeforces Round #364 Hello everybody! Today the second regular rated round based on problems of VK Cup 2016 Final Round will take place. Of course, we have created some more easy problems to fulfill the requirements of different skill levels and make the contest interesting for everyone. The commentators of the previous announcement pointed out that I forgot to thank [user:MikeMirzayanov,2016-07-22] for making Codeforces and Polygon so awesome. I was wrong, Mike, that's really cool :) Scoring distribution will be published right before the start of the contest. We wish you good luck and beautiful solutions! **UPD1**. Scoring for div2: 500-750-1000-1500-2000-2500. Scoring for div1: 500-1000-1500-2250-3000. **UPD2**. The contest is over, congratulations to winners! Div1: 1. [user:ainta,2016-07-22] 2. [user:W4yneb0t,2016-07-22] 3. [user:Petr,2016-07-22] 4. [user:muratt,2016-07-22] 5. [user:kcm1700,2016-07-22] 6. [user:Vercingetorix,2016-07-22] 7. [user:Tinsane,2016-07-22...

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Codeforces Round #317 <img src="http://aimfund.ru/bitrix/templates/aimfund/images/logo.png" style="width:120px; height:179px; float: right;margin: 0 1.0em 1.0em 1.0em;" /> Hi, Codeforces! Codeforces Round 317 will take place on <a href="http://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23317+%5BAimFund+Thanks-Round%5D&iso=20150822T1930&p1=166&ah=2">August, 22 at 19:30 MSK</a>. The round is prepared by AimFund employees: [user:Kostroma,2015-08-19], [user:AlexDmitriev,2015-08-19], [user:yarrr,2015-08-19], [user:gchebanov,2015-08-19], [user:ArtDitel,2015-08-19], [user:Baz93,2015-08-19] and [user:zeliboba,2015-08-19]. Scoring system will be static. Thanks to Mike Mirzayanov([user:MikeMirzayanov,2015-08-19]) for brilliant platforms Polygon and Codeforces, problem coordinator Max Akhmedov ([user:Zlobober,2015-08-19]) and Maria Belova ([user:Delinur,2015-08-19]) for English translation. __Top 200__ div1 participants will be awarded t-shirts. To learn more about AimFund...

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Разбор Codeforces Round #144 Задачи, которые не успели написать, разберу кратко. Задавайте вопросы. [problem:233A] Идея: [user:Gerald,2012-10-14] Реализация: [user:tunyash,2012-10-14] Разбор: [user:Moskupols,2012-10-14] Эту задачу можно было решать разными способами, например, таким: рассмотрим перестановку $p$, в которой $p_i = i$, то есть просто последовательность чисел от $1$ до $n$. Очевидно, для неё условие $p_{p_i} = i$ выполняется всегда. Осталось только преобразовать её таким образом, чтобы выполнялось и второе условие: $p_i \neq i$. Для этого поменяем местами каждые два соседних элемента, т.е. для каждого $k: k*2 \le n$ поменяем местами значения $p_{2k-1}$ и $p_{2k}$. Нетрудно убедиться, что для полученной перестановки оба условия выполняются всегда. [problem:233B] Идея: [user:tunyash,2012-10-14] Реализация: [user:tunyash,2012-10-14], [user:Gerald,2012-10-14] Разбор: [user:Moskupols,2012-10-14] Для начала найдем диапазон значений, которые может принимать $s(x)$. Так как из уравнения ...

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Indian Programming Camp 2020 Hi Everyone, I'm delighted to announce that we will be hosting Indian Programming Camp (IPC) &mdash; 2020 edition online from **November 20th &mdash; November 22nd**. The camp has **no charges** and anyone can **register** and attend. In the past, the IPC camp used to be conducted offline and was mainly targetted towards experienced IOI and ICPC aspirants. You can take a look at the [IPC 2016](https://www.youtube.com/playlist?list=PLi0ZM-RCX5nsTc2Z6woHr5qoF6n3b-thO) and [IPC 2017](https://www.youtube.com/playlist?list=PLi0ZM-RCX5nvImim3_ilsdLOtDDkOWt-X) playlists to get an idea of the format. This year, we are introducing three different tracks &mdash; Div3/Div2/Div1, catering to Beginner/Intermediate/Advanced programmers. Event: **Indian Programming Camp 2020** Dates: **November 20th &mdash; November 22nd, 2020** Platform: **[YouTube](youtube.com)** and **[Unacademy](https://unacademy.com/goal/competitive-programming/LEARNCP)** Tracks: **Div1/Div...

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Mirror of Bubble Cup 13 Finals on Codeforces Hello, Codeforces! Hope you're all safe and well. [Microsoft Development Center Serbia](https://www.microsoft.com/sr-latn-rs/mdcs) is thrilled to announce the finals of the **13th edition of Bubble Cup competition**! Bubble Cup is an international, **ACM-style team contest** aimed at university and high school students.  Contest will take place on [Sunday, 4th of October at 11AM CEST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Bubble+Cup+13+Finals&iso=20201004T11&p1=35&ah=3), virtually. Live results will be available on the official Bubble Cup website (results will be frozen during the last 45 minutes of the competition). Winners will be announced at the closing ceremony. You can find more info on the [BubbleCup website](https://www.bubblecup.org/). Just like the previous editions, this final will be followed by an online mirror competition on Codeforces. Mirror will take place on [Mon...

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Codeforces Round #296 Hi everybody! There will be a Codeforces Round for both divisions today at [standard time](http://timeanddate.com/worldclock/fixedtime.html?day=17&month=3&year=2015&hour=19&min=30&sec=0&p1=166) set up by me. My teammates from ICPC team Moscow SU Trinity [user:sankear,2015-03-17] and [user:malcolm,2015-03-17] helped me a lot while preparing this round, also there were lots of useful tips and advices from [user:MikeMirzayanov,2015-03-17], applause for them. English translation was made by our veteran translator [user:delinur,2015-03-17]. As usual, there will be five tasks for two hours. The scoring will be announced later. See you on the round! I hope that each contestant will be able to find something nice in ongoing problems. **UPD**: Scoring is standard. **UPD2**: Due to technical issues the round is delayed by 15 minutes. We are sorry for an inconvenience. **UPD3**: We are sorry for an inconvenience with the task Div1-D. The pretest #16 wasn't satisfying the constra...

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Infoleague Spring Round 2022 Announcement Hello Codeforces! We would like to invite you to the first (and possibly only) round of Infoleague Spring 2022, the contest starting on Wednesday, March 30th from [12:30 GMT+3](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Infoleague+Spring+2022+Official+Round&iso=20220330T123030&p1=2209&ah=4). The problems in this round have been prepared to train high school students for the upcoming Romanian National Olympiad in Informatics (ONI). **The registration period for this contest starts from [6:30 GMT+3](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Infoleague+Spring+2022+Official+Round+Registration&iso=20220330T0630&p1=2209&ah=6) on Wednesday, March 30th**. This contest has two divisions, Div 1 and Div 2. The Div 2 contest intends to mimic an ONI problemset for 9th and 10th graders, while Div 1 is mainly focused towards challenging 11th and 12th graders. Contest links: [Div1](https://codeforces.com/gym/103634), [Div2](https://codeforces.com/gym/1036...

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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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Editorial Codeforces Round #319 Task A. Div2. It's easy to see that number $x$ can appear in column $i$ only once &mdash; in row $x / i$. For every column $i$, let's check that $x$ divides $i$ and $x / i \le n$. If all requirements are met, we'll update the answer. The complexity is $O(n)$ [Source](http://pastebin.com/yGMTt9KZ) Task B. Div2. Let's consider two cases: $n > m$ and $n \le m$. If $n > m$, let's look at prefix sums. By pigeonhole principle, there are two equals sums modulo $m$. Assume $S_l mod m = S_r mod m$. Then the sum on segment $[l + 1, r]$ equals zero modulo $m$, that means the answer is definitely "YES". If $n \le m$, we'll solve this task using dynamic programming in $O(m^2)$ time. Assume $can[i][r]$ means if we can achieve the sum equal to $r$ modulo $m$ using only first $i - 1$ items. The updates in this dynamic programming are obvious: we either take number $a_i$ and go to the state $can[i + 1][(r + a_i)\ mod\ m]$ or not, then we'll get to the state $can[i + 1][r]$. The ...

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Please allow rated participation of purple-rating users in Div. 2 contests Hi! The main objective of my post is to make most **Div. 2 only** rounds rated for purle users. This is beneficial because it would distinguish their rating better. It would also mean a more frequent participation for those people, which is good for the growth of the plataform. It makes no sense to make a purple coder wait for a Div. 1 round, which is rare due to the difficulty to come up with a Div1 D/E problem, when in most cases those users don't even read these harder problems at all. Another reason is because most Div. 2 rounds are hard enough for people with purple rating. I assume the difficulty of contests should be sufficient to not transform them in a "type race", which means that it is good that few people solve all the problems. I will try to convince you that we can make div2 contests rated for people with higher rating without breaking this principle. **EDIT:** Originally the title of this blog was "Please increase div2 upper rating limit" but this was missl...

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Manthan, Codefest'18, IIT (BHU) Announcement Hello Codeforces, Manthan, Codefest'18 will take place on [contest_time:1037] with a duration of 2 hours (tentative). The round is rated for both Div1 and Div2 participants and will consist of 8 problems. The Department of Computer Science and Engineering, IIT (BHU) is conducting Codefest from 31st August-2nd September. Manthan (मंथन in Hindi, meaning Brainstorming), the algorithmic programming contest under the banner of Codefest, is being held as a special Codeforces round. The round follows regular Codeforces rules. The round has been prepared by [user:hitman623,2018-09-01], [user:karansiwach360,2018-09-01], [user:GT_18,2018-09-01], [user:ezio07,2018-09-01], [user:Enigma27,2018-09-01], [user:csgocsgo,2018-09-01] and me ([user:dhirajfx3,2018-09-01]). Special thanks to [user:praran26,2018-09-01] and [user:dark_n8,2018-09-01] for their contribution in the preparation of the round. We express our heartiest thanks to [user:KAN,2018-09-01], [user:gritukan,2018-09-01], [user:30...

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Challenge for Div2 Students <table> <div style="font-size: 16px;"> Hi all and <span style="color:red;">happy New Year!</span> <br> <p>I am [user:chessmaster,2017-02-03], and ordinary student from Uzbekistan, who has been participating <span style="color:blue;">ACM ICPC</span> semifinals of <span style="color:blue;">NEERC</span> region. During the first attempt, my team managed to solve two problems and was a bit higher than bottom in the scoreboard. However, this year we couldn’t solve anything (let’s not talk about places). At that moment, I realized that NEERC is a hard nut to crack. Being blue (not to mention green and cyan), it is way too early to dream about first-degree certificates or proceeding to Finals. So I said to myself: “Either you raise your rating to 2000 or you skip <span style="color:blue;">ACM ICPC 2017</span>. You won’t even register your team!”. Then I told my friends about this and four of them joined me. Now I want to offer this challenge to all div2 students, who want not only participa...

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Codeforces Round #448(Div.2) Hi everyone! Codeforces Round #448 (Div.2) takes place on [26th of November at 19:05 MSK](https://www.timeanddate.com/countdown/launch?iso=20171126T1905&p0=285&msg=Codeforces+Round+%23448&font=cursive). As usual, Div.1 participants can join out of competition. This is my second round on Codeforces! I advise you to read all of the 5 problems. Hope everyone will find something interesting. I'd like to thank [user:gritukan,2017-11-25] for coordination, [user:igdor99,2017-11-25] for helping me in developing problems. And, surely, thanks to [user:Tommyr7,2017-11-26], [user:Arpa,2017-11-26], [user:gainullin.ildar,2017-11-26] for testing this round. Of course, many thanks to [user:MikeMirzayanov,2017-11-25] for great Codeforces and Polygon platforms. Scoring: **500-1000-1750-2000-2250** High ratings to everybody! **UPD:** Contest is finished. Editorial will be posted soon. **UPD:** [Editorial](http://codeforces.com/blog/entry/56028) Congratulations to the winners!!!...

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Codeforces Round #172 Hello there! Codeforces Round #172 will take place on [Sunday, March 10th at 19:30 MSK(23:30 CST)](http://timeanddate.com/worldclock/fixedtime.html?day=10&month=3&year=2013&hour=19&min=30&sec=0&p1=166). This is my second time participating in prepration a Codeforces Round. Last time assist with [user:WJMZBMR,2013-03-04] is an unforgettable experience. This time, the hardest problems were created by **Jiatai Huang**([user:CMHJT, 2013-03-04]) and others by me and **Yuping Luo**([user:roosephu,2013-03-04]). Testers are [user:Sevenkplus,2013-03-04], [user:WJMZBMR,2013-03-04], [user:pashka,2013-03-04] and [user:Seter,2013-03-13]. We gratefully acknowledge **Gerald Agapov**([user:Gerald,2013-03-04]) for his help in giving advise about the problems, **Delinur** for her help in translating the problems to Russian, and [user:MikeMirzayanov,2013-03-04], who has designed such a powerful platform. Here let me express my personal thanks to the Codeforces community, which has given...

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Codeforces Round #441 (on the problems of Moscow Team Olympiad) Hi everybody, Lasts Sunday there was a 15th [Moscow Team Olympiad](http://olympiads.ru/team), high school students competition based in Moscow that is an elimination contest for All-Russian Team Olympiad. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Open Olympiad, Moscow Olympiad for Young Students and Megapolises Olympiad (rounds [327](http://codeforces.com/blog/entry/21185), [342](http://codeforces.com/blog/entry/23309), [345](http://codeforces.com/blog/entry/43615), [376](http://codeforces.com/blog/entry/47769), [401](http://codeforces.com/blog/entry/50613), [433](http://codeforces.com/blog/entry/54350)). Round will be held at [11:05 UTC on Monday](http://www.timeanddate.com/worldclock/fixedtime.html?day=16&month=10&year=2017&hour=14&min=5&sec=0&p1=166) and will last for 2 hours. Each division will consist of 6 problems. Problems are prepared [user:Andreikkaa,2017-10-15], [user:sender,2017-10-15], [user:Flyrise,2017-10-15], [...

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Codeforces Round #263 Tutorial [Div2 A Appleman and Easy Task](http://codeforces.com/contest/462/problem/A) (Author: [user:wolf_sothe,2014-08-26]) This is a simple implementation problem. You can solve by searching adjacent cells of every cell. [Div2 B Appleman and Card Game](http://codeforces.com/contest/462/problem/B) (Author: [user:wolf_sothe,2014-08-26]) This is simple greedy problem, but it seemed to be reading-hard. The statement says, "Choose K cards from N cards, the score of each card is (the number of cards which has the same character in <b>K</b> cards. (not in N cards)" It is clear that this total score is (the number of 'A' in K cards)^2 + (the number of 'B' in K cards)^2 + ... + (the number of 'Z' in K cards)^2 This value will be maximized by the simple greedy algorithm, take K cards from most appearred character in N cards, the second most appearred character in N cards, and so on. [Div1 A / Div2 C Appleman and Toastman](http://codeforces.com/contest/461/problem/A) (Author: [user:ho...

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Codeforces Round #104 - Editorial <p</p><p><b>DIV2-A Lucky Ticket:</b></p><p>In this problem everything is obvious: if all digits are lucky and sum of the digits of the first half equals to the sum of the digits of the second half, then answer is YES, in other case - NO. All this can be checked by single loop through all the digits. </p><p><br /></p><p><b>DIV2-B Lucky Mask:</b></p><p>You can see that, in worst case, the answer will be equal to $177777$. It can't be greater. So, only thing you need is to write some function $F(x)$ which will return mask of the $x$. After that you need to write such kind of code: </p><p><br /></p><p>$x$ = $a+1$;</p><p>while ($F(x)$ is not equal to $b$)</p><p>increase $x$;</p><p><br /></p><p>and $x$ will contain the answer.</p><p><br /></p><p><b>DIV2-C DIV1-A Lucky Transformation:</b></p><p>You need to find two numbers: $c47$ (number of such positions $i$, that $a_i = 4$ and $b_i = 7$) and $c74$ (number of such positions that $a_i = 7$ and $b_i = 4$). After that the result will be $max(c4...

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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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CP is hard? Try breaking both hands I recently [broke both of my hands](https://codeforces.com/blog/entry/124704), which forced me to type rather slowly, so I've had to come up with some strategies to optimize my contest performance and so on. To be honest, it wasn't that bad (and it's less noticeable the longer a contest is, as implementation speed becomes less relevant. For example, I got 11th place on a 5 hour individual contest at the Brazilian ICPC Summer School a week ago) but I'm still very happy to announce that they removed both my casts today and I'm finally back to "properly" coding using both hands. I say "properly" in quotes because I'm not really back to 100% yet, as months of immobilization caused my muscles and ligaments to slightly atrophy, which causes some stiffness and pain when I move the affected joints. This is apparently easily solved by a month of rehab :^). Also, because of the way the bone came back together, the index finger on my right hand is now slightly rotated towards my middle fing...

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Codeforces Round #415 Editorial [tutorial: 810A] <spoiler summary="Setter's code"> ~~~~~ int n, k, s = 0; cin >> n >> k; for (int i = 0; i < n; ++i) { int x; cin >> x; s += x; } for (int ans = 0;; ans++) { int a = 2 * (s + ans * k); int b = (2 * k - 1) * (ans + n); if (a >= b) { cout << ans; return 0; } } ~~~~~ </spoiler> First accepted [user:Zhigan,2017-05-21]. [tutorial: 810B] <spoiler summary="Setter's code"> ~~~~~ for (int i = 0; i < n; i++) { cin >> k[i] >> l[i]; a.push_back(make_pair(min(2 * k[i], l[i]) - min(k[i], l[i]), i)); } sort(a.rbegin(), a.rend()); long long ans = 0; for (int i = 0; i < f; i++) { int pos = a[i].second; ans += min(2 * k[pos], l[pos]); } for (int i = f; i < n; i++) { int pos = a[i].second; ans += min(k[pos], l[pos]); } cout << ans; ~~~~~ </spoiler> First accepted [user:polygonia,2017-05-21]. [tutorial: 809A] <spoiler summary="Setter's code"> ~~~~~ st[0] ...

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About Div. 4 Rounds and other useful suggestions for further improvement Given [user:MikeMirzayanov,2020-05-07]'s [Div 4 contest announcement](http://codeforces.com/blog/entry/77028) and [user:Errichto,2020-05-07]'s [suggestion for lower bound for Div 2](http://codeforces.com/blog/entry/77035), I decided to come up with some ideas to further improve this update. Firstly, I'd like to say that Div. 4 contests are a great addition for people who have absolutely no idea about competitive programming and the ability of being able to solve more than just one problem will definitely make new people more confident when it comes to problem solving. However, this change will definitely bring lots of new contestants to Codeforces, and some measures will have to be taken in order to deal with the new change. As [user:Errichto,2020-05-07] suggested, a rating lower bound would be beneficial because it partly solves the rating inflation and also because it will generate less queue. Starting from this point of view, I'd like to suggest further improvements whic...

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Codeforces Round #559 Hello, Codeforces! I'm glad to invite you to [contest:1158] and [contest:1159], which will be held on [contest_time:1158]. The round will be rated for both divisions (I hope). All problems were written and prepared by me. Thanks to [user:aleks5d,2019-05-10], [user:TLE,2019-05-10], [user:sunset,2019-05-10], [user:Sooke,2019-05-10], [user:Peltorator,2019-05-10] for testing problems and good advice, [user:300iq,2019-05-10] for round coordination and help with preparation and [user:MikeMirzayanov,2019-05-10] for great systems Codeforces and Polygon. You will be given 6 problems in both divisions and 2 hours to solve them. Please, read all the problems. Good luck, have fun and I wish everyone high ratings! The scoring distribution will be announced closer to the beginning of the round. **UPD** The contest finished, contgratulations to the winners: Div1: 1. [user:mnbvmar,2019-05-12] 2. [user:ecnerwala,2019-05-12] 3. [user:ainta,2019-05-12] 4. [user:ksun48,2019-05-1...

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Codeforces Beta Round #91 - Analysis <div><b>1. [[problem:122A,Lucky Div (Div2 A)]]</b></div><div><br /></div><div>In this problem you just need to loop through the integers $i$ from $1$ to $n$ determine, is $i$ lucky, if yes, then try, if $n$ mod $i$ = $0$, then answer is &quot;YES&quot;. If there are no such $i$, answer is &quot;NO&quot;.</div><div><br /></div><div><b>2.&nbsp;[[problem:122B,Lucky Substring (Div2 B)]]</b></div><div><br /></div><div>Notice, that answer is either one digit or -1. So, if there are no $4$ and $7$ digits, then answer is -1. Else, if there is more or equel number of digits $4$, then answer is $4$, else answer is $7$.</div><div><br /></div><div><b>3.&nbsp;[[problem:121A,Lucky Sum (Div1 A + Div2 C)]]</b></div><div><br /></div><div>Let generate all lucky number between $1$ and $10^10$. Consider all segment&nbsp;$[1; L0]$, $[L0+1; L1]$, $[L1+1; L2]$ ... Then the result equals to product of intersection of segments&nbsp;$[1; L0]$ and $[1; n]$ by $L0$ plus size of intersection of $[L0+1; L1]$ and &n...

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Problemsetter's Memoir Preparing a contest is not as popular a topic as the perennial question of "how to become red in three months", but still it stirs some interest in Codeforces community now and then. Earlier I've written about [preparing Surprise Language Round](http://codeforces.com/blog/entry/4290) and about [emotional aspect of problemsetting](http://codeforces.com/blog/entry/3857); now it's time to share some facts about running regular contests. ### Problems > How much time does it take to prepare, select, recall or find problem ideas? > How much experience solving competitive programming problems is necessary to be confident about inventing problems of your own? Idea generation is a long-term, nearly continuous process. A couple of years ago when I was still an active problemsetter I used to create ideas from literally everything (a squirrel running... hey, this could be a great problem! &mdash; seriously, the problem is still there in my drafts, and a pretty comp...

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Analysis Codeforces Beta Round #75 <p><strong>Problems A(div2), B(div2)</strong><br></p>In these problems you should only realize what was written is the statement. In problem <em>B</em> wasn't recommended to use BigInteger in Java because of slow speed.<br><p><strong>Problem C(div2), A(div1)</strong><br></p>In this problem letters from $s1$ should be taken greedily: take the left letter from the right of the last used letter, if there is no necessary letter from the right of the right used letter the the search should be started from the beginning of string $s1$ and the answer should be increased by one. But the brute solution get $TL$ and have complexity $O(Ans*|s1|)$.&nbsp;<br><br>This solution can be optimized using the following way. For every position in $s1$ let's precalculate positions of the closest letters from the right of it from the alphabet. It can be done by moving from the right to the left ins $s1$ and remembering the last position of every type of symbol. This solution have complexity $O(|s1|*K + |s2|)...

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Codeforces Round #417 (Div. 2) Hello Codeforces! I would like to invite you to Codeforces Round #417 that will take place tomorrow [on June 1st, 2017 at 17:05 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codeforces+Round+%23417+%28Div.+2%29&iso=20170601T1705&p1=166&ah=2). This is my first round. Great thanks to [user:KAN,2017-05-31] for his efforts and help in the round preparation, [user:mike_live,2017-05-31] and [user:gainullin.ildar,2017-05-31] for testing the problems, and [user:MikeMirzayanov,2017-05-31] for the awesome Codeforces and Polygon platforms. The round is rated for the second division. Participants from the first division can take part out of competition. As usual, the participants will be given 5 problems and two hours to solve them. I hope you will find the problems challenging and interesting! **UPD 1**: Scoring disrtibution: 500 &mdash; 1000 &mdash; 1500 &mdash; 2000 &mdash; 2500. **UPD 2**: Due to a technical issue, the contest is delayed by 10 minutes. *...

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Codeforces Round #363 Dear friends! We are glad to invite you to take part in Codeforces Round #363, featuring some problems of the VK Cup 2016 Final Round that took place in Saint Petersburg at the beginning of July. The second part of the problemset will be used to conduct Codeforces Round #364. Of course, we made some new problems to complete the set to fulfill the requirements of the regular round and it now contains problems of the appropriate difficulty for participants of any color. We will obey the good old tradition to publish the scoring distribution right before the start of the competition. We wish you good luck and an interesting contest! **UPD1**. Scoring distribution will be standard in both divisions 500-1000-1500-2000-2500-3000 (yes, there will be six problems featured in both div1 and div2). **UPD2**. Problems were prepared for you by [user:MikeMirzayanov,2016-07-19], [user:Errichto,2016-07-19], [user:fcspartakm,2016-07-19], [user:qwerty787788,2016-07-19] and [user:Stonefean...

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Solutions for Codeforces Round #125 **Div2 A.** You can just output "0 0 n". Author is ~Alex_KPR,2012-06-23 [cut]. **Div2 B.** You should check for every circle of one ring: it have intersections with another ring or not. So, there are 4 checks. There are 2 cases: 1. circle is inside of ring; 2. circle is outside of ring and ring is outside of circle; 3. circle is outside of ring and ring is inside of circle. If at least one of these cases is performed, circle is good. You can easily do checks following way. Let us $d$ be a distance between centers of ring and circle, $r_1$ and $R_1$ are inside and outside radii of ring, $r$ be radius of circle. Then conditions for all cases will be 1. $d+r \le r_1$. 2. $r+R_1 \le d$. 3. $d+R_1 \le r$. You can check all conditions in integers using squares of distances. Author is ~Alex_KPR,2012-06-23 **Div2 C.** **Div1 A.** The first solution. Consider sequence $a_0=1$, $a_i=a_{i-1} k + b$: $a_0$, $a_1$, $a_2$, ..., $a_n=z$. ...

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