Stream I want to try streaming competitive programming. The goal is to make it educational so I will be talking a lot, also answering (at least some) questions. I'm planning three completely different streams to see what format to use: 1. Solving random easy-medium problems. 2. Solving old problems from Polish olympiad. 3. Post-contest stream, assuming I'm a setter or tester of a contest. Similar to what [user:scott_wu,2018-09-27], [user:ecnerwala,2018-09-27] and [user:stevenkplus,2018-09-27] did. Any thoughts, ideas? The first stream will most likely be on Sunday, starting around 7-8pm CEST. I will use Twitch and talk in English only. These first streams should show me and you whether it's cool and useful, and whether I like doing it. Also, I will try to make the video accessible later. **--- UPDATE ---** The first stream will start on Saturday at 10am CEST (check your [timezone](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Errichto+Stream+%231&iso=2018...

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Sums and Expected Value — part 1 part 2: https://codeforces.me/blog/entry/62792 Watch my lecture-stream tomorrow (Thursday) at [14:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=EV+lecture+1&iso=20181025T14&p1=262) &mdash; <s>[https://www.youtube.com/watch?v=qdlPY37MBPo](https://www.youtube.com/watch?v=qdlPY37MBPo)</s> [https://www.youtube.com/watch?v=U_h3IjreRek](https://www.youtube.com/watch?v=U_h3IjreRek). I will go through theory and problems from this blog. The only prerequisite is knowing what is probability. The next (harder) part on Monday. The video will be available later, with timestamps for each problem &mdash; so you don't have to watch everything. ### Definition of EV Let's say we bought a lottery ticket for 2$. We will win 10$ with probability 10%, and 20$ with p-bility 2%. On average, it gives us $0.1 \cdot 10 + 0.02 \cdot 20 = 1.4$, so we are worse off after buying the ticket. The computed average is called the expected value. The expected value (EV, expecta...

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Huawei IOI Camp 2022 Hi. I'm organizing an online IOI-preparation camp in collaboration with Huawei. Every day will be a 5-hour virtual contest, then my problem analysis, and sometimes a lecture. There will be at least 4 contests and 2 lectures. We will do some old IOI contests (2013?) from the [IOI archive](https://codeforces.me/blog/entry/104593), CEOI (2015-2016?), or maybe JOI/JOISC &mdash; to be decided this weekend. I don't want to do recent years like 2021 because most participants already covered it. The example lecture topics are those from Range Queries or Trees in [Usaco Guide Platinum](https://usaco.guide/plat). The camp is free for IOI 2022 participants. For everybody else, the video recordings will be posted on Youtube after the camp. By participating you get the live experience (Discord, asking questions, competing with others, leaderboards). **Dates**: 25.07-2.08 (updated) **Time** of every analysis/lecture: [14:00 UTC / 16:00 CEST](https://www.timeanddate.com/worldclock...

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My Streams in Summer 2025 Hi, I'm back to streaming :) In particular, I'm going live in 20 minutes. You can watch on [Twitch](https://www.twitch.tv/errichto) or [Youtube](https://www.youtube.com/errichto2). The recording will remain available on YT. #### June - [recording](https://youtu.be/p1DYJaPcsO4) 27.06 &mdash; Linux & Geany setup - [recording](https://www.youtube.com/live/J-Cjb4dkdmQ?si=W-KbE7Bus3X0ghYz) 28.06 &mdash; short test stream, solving 1-2 problems - [recording](https://youtube.com/live/VgXiMsX6YHE) 29.06 &mdash; div2 problems - [recording](https://youtube.com/live/B-6_16kkCkA?feature=share) 30.06 &mdash; div1 problems #### July - [recording](https://youtube.com/live/LQuhmiJDFj4?feature=share) 6.07 &mdash; (easy) div2 problems - [recording](https://www.youtube.com/watch?v=O0qbgoDUj0g) 7.07 &mdash; (hard) [problem:2119D] and [contest:2124] C-E - [recording](https://www.youtube.com/watch?v=32xFpRrexdY) 8.07 &mdash; (easy) [contest:2123] - [recording](https://youtube.com/live/k...

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My Summer CP School, rating 1000-2200 Hi, I'm going to teach competitive programming classes this Summer, starting with a 4-week batch to see how it goes. I hope to make 2 or 3 groups of ~12 students, each group aimed at some CF rating. We will use problems from Codeforces, CSES, Atcoder, Polish olympiad (only higher group), and my modifications and follow-ups. There will be homework, some to be discussed next lesson. - Dates: June 24 to July 19 (4 weeks) - Time: morning-noon in Europe - 2-3 lessons per week, 1.5h or 2h each - Price: around 20 USD per hour, 260-440 USD total per person - Platform: Discord and/or Google Meet Please fill [this form](https://forms.gle/v1q7qZKU1YnNWRbaA) to get a 5% early-bird discount. I will use the results to choose and announce groups (difficulty and frequency) in 1-2 weeks. Feel free to ask questions in the comments, or DM me. <spoiler summary="regarding the idea of USACO classes"> I already mentioned [here](https://codeforces.me/blog/entry/129009) my plan to do USAC...

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My Coding Streams in September 2020 You can watch me live on https://www.twitch.tv/errichto or see stored broadcasts on https://www.youtube.com/errichto2. I will start with a week of daily streams and then it's just when I have time. * [September 8, 18:30 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200908T1830&p1=262) &mdash; Codeforces Round #668 ([recording](https://youtu.be/h8W0omsVETo)) * [September 9, 17:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200909T17&p1=262) &mdash; chatting with viewers, random stuff ([recording](https://youtu.be/9Z8MgTBmOIs)) * [September 10, 17:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200910T17&p1=262) &mdash; 1v1 lockout against [user:Merkurev,2020-09-09] ([recording](https://youtu.be/lY2-stOhkVQ)) * [September 11, 17:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200911T17&p1=262) &mdash; recent Codechef lunchtime and cook-off contests ([recording](https://youtu.be/xc_RBsSw2mI)) * [Sep...

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My Coding Streams in May&June You can watch me on https://www.twitch.tv/errichto or https://www.youtube.com/errichto2. There is schedule with countdown on Twitch. Most likely I will stream in May on Tuesday mornings and Sunday evenings. - [May 3, 16:45 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200503T1645&p1=262) &mdash; **Codeforces hard** (solving hard problems because the round was moved) - [May 5, 9:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200505T09&p1=262) &mdash; **Boring Programming Stream** (planning videos, fixing chatbot, maybe learning Berlekamp–Massey) - [May 10, 18:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200510T18&p1=262) &mdash; **Atcoder hard** (Grand Contest 43?) - [May 12, 9:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20200512T09&p1=262) &mdash; **Atcoder hard** or something similar to practice for Google Code Jam. - [May 17, 18:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.htm...

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August Classes & Huawei IOI Camp 2024 Hello, everybody. <spoiler summary="August CP School, cancelled"> August CP School ---------------- I'm again organizing group classes after trying the format [last month](https://codeforces.me/blog/entry/129878). There will be problem-solving, homework, and recordings. I can make a lecture on some topic per requests. There will be two groups. You can attend both, just don't spoil anything in the lower group. (Btw. I also want to do 3-month weekly classes after Summer.) 1. Medium group: [16:00-17:30 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20240808T16&p1=262&ah=1&am=30), 90-minute lessons, CF max rating 1500-1800 2. Hard group: [18:00-20:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20240808T18&p1=262&ah=2), 2-hour lessons, CF max rating 1900-2200 - Dates: August 8 to 26 or 29 (6 meetings in total) - Every Monday and Thursday - Price: 200 USD per person (so around 20$ per hour, or 13$ if you're going to attend both groups)...

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Sums and Expected Value — part 2 ### Instruction I recommend this blog also for red users. Read the theory and problems below, try to solve them. For solutions and extra insight/tips, watch my stream on Monday or watch the video later. If you aren't familiar with EV or summing problems, see part 1 first: [http://codeforces.me/blog/entry/62690] (http://codeforces.me/blog/entry/62690). I will stream a lecture on Monday at [14:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=EV+lecture+2&iso=20181029T14&p1=262) &mdash; [https://www.youtube.com/watch?v=HDk6zQw0Rdo](https://www.youtube.com/watch?v=HDk6zQw0Rdo) (also [Twitch](https://www.twitch.tv/errichto)). I will go through theory and problems from this blog. ### Expected Value theory, part 2 We roll a 6-sided die. Remember, EV of square of the number of pips is something different than square of EV: $$E(X^2) = \frac{1+4+9+16+25+36}{6} = 15.166666\ldots$$ $$E(X)^2 = (\frac{1+2+3+4+5+6}{6})^2 = 3.5^2 = 12.25$$ Two events are ...

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And three streams this week Hi. Even more streams are coming. For notifications, subscribe to my secondary channel for streams [Errichto 2](https://www.youtube.com/errichto2), or you can watch me on [Twitch](https://www.twitch.tv/errichto). **Stream 1** &mdash; Monday [at 12:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20190520T12&p1=262), I want to check out coding interview platforms like Leetcode. Here's [Youtube link](https://www.youtube.com/watch?v=1PhErzqrY6c). **Stream 2** &mdash; Tuesday [at 9:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20190521T09&p1=262). Algo research and writing old editorials. Links to [part 1](https://www.youtube.com/watch?v=XWf9DCMnpFM) and [part 2](https://www.youtube.com/watch?v=5rW-t3KFLM0) (the stream stopped for a few seconds and the new one started). **Stream 3** &mdash; Friday [at 12:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20190524T12&p1=262). Solving Codeforces problems, mainly around <s>div...

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DP Group Class in August 2025 _The blog publish date is incorrect, should be around 12.07.2025. CF saved the draft date._ Hi, I'm organizing paid group classes on Dynamic Programming in August. Last year, I did something similar with general problem-solving ([link](https://codeforces.me/blog/entry/129878)). There will be two groups of different style and difficulty. Each group gets 8 lessons of 1h30m each, from 28.07.2025 to 24-31.08.2025. Group size up to 12 people. You get access to recordings and problems from both groups, but you should actively attend only one. There's a lot of homework, some to be discussed next lesson. I will create new original CF/Polygon problems, especially for the easy group. These problems will eventually be published for everybody! **Price**: 250 EUR with a small country-based discount. **Registration**: You should pay via [link (Stripe)](https://buy.stripe.com/7sY3cx2nD5Oh8CQ7w96wE03) and choose the group there. I will send you the Discord invite link via e-mail. Co...

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After-stream thoughts Hello again. Next stream will start tomorrow (Wednesday) at 2pm CEST ([your timezone](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Errichto+Stream+%233&iso=20181003T14&p1=262)), solving problems from POI 22, round 1 ([link](https://szkopul.edu.pl/p/default/problemset_eng/oi/22)). It will be on my [Youtube channel](https://www.youtube.com/channel/UCBr_Fu6q9iHYQCh13jmpbrg). I did two streams this weekend that you can now find on my youtube [channel](https://www.youtube.com/channel/UCBr_Fu6q9iHYQCh13jmpbrg). The first with quite easy Codeforces problems that I solved from scratch (I haven't seen them before), also implementing them. The second one with a bit harder Topcoder problems that I've solved before, but I didn't necessarily remember the solution now &mdash; and for those I only described the solution, without implementation. The streams were fine but there are a lot of things to improve. I wanted to see two things: 1. Can I stream? Am I able to try to sol...

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[Tutorial] Полиномиальное хэширование + разбор интересных задач Здравствуйте! Этот пост написан для всех тех, кто хочет освоить полиномиальные хэши и научиться применять их в решении различных задач. Я кратко приведу теоретический материал, рассмотрю особенности реализации и разберу некоторые задачи, среди них: 1. Поиск всех вхождений одной строки длины $n$ в другую длины $m$ за $O(n+m)$ 2. Поиск наибольшей общей подстроки двух строк длин $n$ и $m$ $(n \ge m)$ за $O((n+m \cdot log(n)) \cdot log(m))$ и $O(n \cdot log(m))$ 3. Нахождение лексикографически минимального циклического сдвига строки длины $n$ за $O(n \cdot log(n))$ 4. Сортировка всех циклических сдвигов строки длины $n$ в лексикографическом порядке за $O(n \cdot log(n)^2)$ 5. Нахождение количества подпалиндромов строки длины $n$ за $O(n \cdot log(n))$ 6. Количество подстрок строки длины $n$, являющихся циклическими сдвигами строки длины $m$ за $O((n+m) \cdot log(n))$ 7. Количество суффиксов строки длины $n$, бесконечное расширение которых совпадает с бесконечным расшир...

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

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Olympiad Classes by Harbour.Space Hi. I'm excited to announce my partnership with Harbour.Space, which will include free Olympiad classes! I will teach two groups: - **Easy**: A course on competitive programming. You'll learn and practice algorithms, including topics from the USACO Guide [Silver](https://usaco.guide/silver) and [Gold](https://usaco.guide/gold). Prerequisites: C++, BFS, DFS, binary search. - **Hard**: We will mostly solve Olympiad problems, and cover topics from the USACO Guide [Platinum](https://usaco.guide/plat) and [Advanced](https://usaco.guide/adv). This group is aimed at students who want to get an IOI medal. The first semester will last from September until December, around 15 classes per group. As an optional pre-course, the Easy group will start next week (17.08.2026) with a few introductory classes in the second half of August. - Time: Mondays (Easy) and Tuesdays (Hard) at [16:00-17:30 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20260901T16&p1=262&ah=1&am=30...

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Codeforces Round #262 (Div. 2) Editorial [problem:460A] At this problem you need to model what written in statements. Also, it can be proved, that answer can be calculated using formula: $n + \lfloor\frac{n - 1}{m - 1}\rfloor$ , where $\lfloor x \rfloor$ is the integer part of $x$. [submission:7536107] [problem:460B] Obviously $S(x)$ can take only integer values and $ 1 \le S(x) \le 81 $. Let's check $S(x)$ from $1$ to $81$, and calculate $ B*S(x)^{A} + C$. After that if sum of digits of this number is equal to $S(x)$, it is positive and less than $10^9$, than it is a solution. There could be bug because of using C++ pow() function. [submission:7536153] [problem:460C] Note,that answer is positive integer not greater than $10^9+10^5$. Using binary search on answer, we will find answer. Really, we can check in $O(n)$ if some height is achievable. We go from left to right. For current flower we calculate how much times it need to be watered to stand not lower than checking value. If cuurent flower nee...

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Задача о максимальном потоке В этом посте я расскажу о четырех основных и простых алгоритмах поиска максимального потока, к каждому алгоритму прилагается описание работы, псевдокод, нестрогое объяснение корректности, реализация на C++11, и ссылки на задачи. ### I. Задача Пусть дан граф $G=<V,E>$ и две вершины $s,t \in V$, которые в дальнейшем будем называть исток и сток, и каждому ребру из вершины $a$ в вершину $b$ сопоставлена пропускная способность $c_{a,b}$. Определим сопоставление каждому ребру $<a,b>$ числа $g_{a,b}$. Назовем это сопоставление потоком, если для каждого ребра $<a,b>$ верны два утверждения: <br> 1) $0 \le g_{a,b} \le c_{a,b}$ <br> 2) $ \sum_{i \in V} g_{i,a} = \sum_{i \in V} g_{a,i} \forall a \in V \setminus \\{ s,t \\} $ <br> Величина потока равна $ \sum_{i \in V} g_{s,i} = \sum_{i \in V} g_{i,t} = |F|$. Задача &mdash; вычислить $|F|$ и все $g_{a,b}$. ### II. Метод проталкивания потока #### a) Алгоритм Форда-Фалкерсона Пусть дан граф с пропускными способностями. Будем хранить е...

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

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<s>Quantum</s> Google Hash Code 2018 recap stream Sadly, after spending a few hours learning about quantum programming, I decided to cancel the stream. Maybe I would be able to solve some problems in the warm-up round, but certainly, I don't have enough knowledge to make a stream about it, and I'm afraid I would say something incorrect multiple times and thus cause damage to viewers. I'm extremely sorry for that. Instead, I will talk about the Google Hash Code competition. I competed last year with a success. Our team won the qualification round and we were 6-th in the final round (I hope I remember that correctly because I can't find the standings). I'm going to go through the problems from that 2018 edition, talk about my codes, and I will give general advice for the contest. If you want to participate this year, you must hurry &mdash; the registration closes tomorrow (on Monday)! Registration [link](https://codingcompetitions.withgoogle.com/). The stream starts at [12:00 CET](https://www.timeanddate.com/worldclock/fixed...

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Huawei IOI Camp 2023 Here's [the previous edition](https://codeforces.me/blog/entry/104746) and [the video recordings](https://youtube.com/playlist?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH) (CEOI 2016, 2017, 2022, two lectures). Hi. I'm again conducting an online IOI preparation camp in collaboration with Huawei. Every day will be a 5-hour virtual contest, the problem analysis, and sometimes a lecture. Contests will consist of POI problems, and there might be a single day from BOI or CEOI. The example lecture topics are those from Range Queries or Trees in [Usaco Guide Platinum](https://usaco.guide/plat). The camp is free for IOI 2023 participants and coaches. You can register a few extra students if you're a country team-leader (then send me a msg in CF or email at [email protected]). There will be a Discord server and a leaderboard. For everybody else, the video recordings will be posted on Youtube after the camp. **Dates**: around 8-16.08 **Time** of every analysis/lecture: [14:00 UTC...

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2026 Codeforces Rating Distribution With Advanced Analytics! Hello, Codeforces ! I'm excited to share my first contribution to the community: a complete analysis of Codeforces rating distributions, as the last one I know about is [this one from 2024](https://codeforces.me/blog/entry/126802). After several days of collecting and processing data through the Codeforces API, I built a set of analytics covering user rating brackets, average time needed to reach specific rating milestones, and other interesting insights about progression on the platform. I’m also looking to build a community around future projects, learning programming, and helping each other improve. No matter your current rank on Codeforces, you’re welcome to join our newly created [Discord server](https://discord.gg/9RJHWfYUw9) ! Now let's get started with the data. I collected information only for users who have participated in at least 6 contests. I also categorized them based on their recent activity: 6 months, 1 year, 3 years, and all time. If interested in what s...

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

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AtCoder & LeetCode & Codeforces streams in February '20 I'm back to streaming and I plan the following three problem-solving streams, each lasting around 5 hours: - [At 8am CET on Thursday, February 6](https://www.timeanddate.com/worldclock/fixedtime.html?msg=atcoder+easy&iso=20200206T08&p1=262&ah=5) AtCoder easy problems (ABC), including the most recent [ABC 153](https://atcoder.jp/contests/abc153). - [At 8am CET on Monday, February 10](https://www.timeanddate.com/worldclock/fixedtime.html?msg=atcoder+difficult&iso=20200210T08&p1=262&ah=5) AtCoder hard problems (AGC), including the most recent [AGC 41](https://atcoder.jp/contests/agc041) by tourist. - [At 8am CET on Thursday, February 13](https://www.timeanddate.com/worldclock/fixedtime.html?msg=leetcode&iso=20200213T08&p1=262&ah=5) LeetCode recent problems. I will think out loud and talk about solutions, sometimes with implementation too. Streams 1 and 3 are meant to be educational, while stream 2 will be more of me thinking and struggling. I will not do virtual participation beca...

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Programming languages of reds and why we need more diversity I was considering trying to use Python on Codeforces, so I wanted to find a top rated contestant who uses Python as their main language. **Turns out no red contestant uses Python as their main language**. [I compiled this list of who uses which language.](https://gist.github.com/IAmWave/01603900db33d38a17c553c78d40076e) Not surprisingly, C++ dominates &mdash; about 95% reds use it: ~~~~~ C++: 262 Java: 12 Python: 3 C#: 1 ~~~~~ *Note that all three Python users were actually just messing around with the language recently, but they use C++ as their primary language. See the gist to see who uses which language + which compiler/version.* I think this is a shame, because there are many wonderful languages that simply don't get used because people fear they are slower than C++. Many problems are designed in a way that requires careful optimization even in C++ and are simply not solvable in other languages.fr I think having execution time multiplied by a constant ...

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Lockout Stream E01 feat. tourist, Radewoosh, majk, Egor I will host my first lockout stream on [Sunday, June 28, 19:00 CEST / 20:00 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Lockout+E01&iso=20200628T19&p1=262), featuring [user:tourist,2020-06-27], [user:Radewoosh,2020-06-27], [user:majk,2020-06-27] and [user:Egor,2020-06-27]. I'm not sure if we will use Codeforces or Atcoder problems. You can watch it live on https://www.twitch.tv/errichto and later on youtube. Watch previous streams organized by [user:ecnerwala,2020-06-27] (not alone), more info in blogs [one](https://codeforces.me/blog/entry/78799), [two](https://codeforces.me/blog/entry/77173) and [format/rules](https://codeforces.me/blog/entry/72557). **EDIT** Congratulations to [user:Egor,2020-06-28] for the win! You can watch the recording on Youtube https://youtu.be/N7ec-OoxvHg I was a great experience, you should expect the next lockout at the end of July :)

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Two streams this week Hi. I will make two streams this week. Both will be on my [YT channel Errichto 2](https://www.youtube.com/channel/UC2D_ekI79trchAxgRq5mwpQ/) and on [Twitch](https://www.twitch.tv/errichto). My streams will usually be on that second YT channel, while my main channel is for short educational videos, also outside of competitive programming. **Stream 1** &mdash; Thursday [at 9am](https://www.timeanddate.com/worldclock/fixedtime.html?msg=PSUT+Coding+Marathon+2019&iso=20190516T09&p1=262&ah=5), virtual participation of PSUT Coding Marathon 2019 with commentary, just like Atcoder DP stream. The contest is in GYM ([link](https://codeforces.me/gym/102191)). The original announcement by [user:2-SAD,2019-05-15] is [here](https://codeforces.me/blog/entry/66771). **Stream 2** &mdash; Friday [at 2pm](https://www.timeanddate.com/worldclock/fixedtime.html?msg=BPS&iso=20190517T14&p1=262), boring programming stream: maintaining and planning my YT channel, checking out blogs, <s>checking out n...

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Among Us & Regular Algo Streams Hi. I have a few announcements. Among Us stream on [Sunday, 20:00 CEST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20201004T20&p1=262) (just after CF 675 div2). The current team is me, [user:Egor,2020-10-03], [user:kostka,2020-10-03], [user:tmwilliamlin168,2020-10-03], [user:alexwice,2020-10-03], [user:xiaowuc1,2020-10-03], [user:SecondThread,2020-10-03], [user:Reyna,2020-10-04], [user:ssense,2020-10-04], [user:the_white_devil,2020-10-04], [user:SlavicG,2020-10-04], [user:gupta_samarth,2020-10-04], [user:lior5654,2020-10-04]. See you in the chat! https://www.twitch.tv/errichto I stream programming regularly now: every Tuesday (hard Atcoder upsolving), Thursday (coding interviews) and Saturday (easy Codeforces problems), always starting at [9:00 PST / 18:00 CEST / 21:30 IST](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20201003T18&p1=262). You can import my [google calendar](https://calendar.google.com/calendar/embed?src=0qldhlvr0oqd867pdi8nkm8s04%40gro...

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Harbour.Space IOI Camp 2026 - [2022 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH) &mdash; CEOI 2016, CEOI 2017, CEOI 2022, optimization problems, segment tree nodes - [2023 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eAN_QrR5MKnaZROHVSCaQiL) &mdash; POI 2019, POI 2022, CEOI 2018, graphs - [2024 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eCfvefczNWB-c-Af3BUSH0x) &mdash; POI 2016, POI 2019 mix, POI 2023, IOI 2014, lazy propagation, sweep line, partial dp/bfs (Bombs) - [2025 recordings](https://www.youtube.com/playlist?list=PLLnK7ZZWZ74k) &mdash; POI 2018, IOI 2015, CEOI 2019, Convex Hull Trick Hi! I'm running an online IOI camp for the fifth time. This edition is sponsored by Harbour.Space Institute of Technology. It's free for IOI participants and coaches. We also accept participants of regional olympiads like APIO, EGOI, BOI and CEOI 2026. Every day will be a 5-hour virtual contest, the problem analysis, and sometimes a lecture. ...

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Sunday POI 18-2 stream Hi. Thanks to [user:kostka,2019-02-02], this weekend you can participate virtually in an old edition of Polish olympiad: POI XVIII, stage 2. There are two days of a contest, Saturday and Sunday, 9-14 CET ([check your timezone here](https://www.timeanddate.com/worldclock/fixedtime.html?msg=day+1&iso=20190202T09&p1=262&ah=5)). An hour after the contest ends on Sunday (so, [15 CET](https://www.timeanddate.com/worldclock/fixedtime.html?msg=POI+18-2+stream&iso=20190203T15&p1=262&ah=4)), I will talk about problems from both days in a stream. You can watch me on [Youtube](https://www.youtube.com/errichto) and [Twitch](https://www.twitch.tv/errichto). Create an account in Szkopul first, [link](https://szkopul.edu.pl/c/tren18/join/RMQAKCjHhr1ceqVxywNIU5Kv/?fbclid=IwAR3kWUTGwUUClbAqgM0fHZQzwNyNLSf9Q9KxbiDytVVErhqz9KQ4wf7FYes). The statements will be both in Polish and English, or the link to the English version will be provided as an announcement. If you can't participate, I still rec...

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Invitation to CodeChef Starters 262(7 stars — Rated for all) — 28th October We invite you to participate in [CodeChef's Starters 262](https://www.codechef.com/START262), this Wednesday, 28th October, 7 stars — Rated for all. **Time:** [8:00 PM — 11:00 PM IST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=CodeChef+Starters+262&iso=20261028T20&p1=176&ah=3) The problems have been entirely authored by Nikhil [user:Mr._p,2026-05-12] Soni and Khan [user:Hyder1102,2026-05-12] Hyder (me!). This time, the problems on the harder side are Nikhil's. We are pleased to present the contest to the community and hope you enjoy solving the problems! Of course, Nishank [user:IceKnight1093,2026-05-12] Suresh helped us a lot in basically all aspects of hosting this contest. I forgot to mention him last time :( ... Thanks a lot, IceKnight!!! And thanks to my beloved **Web Enthusiasts' Club**, for greatly influencing the CP culture here at NITK. The club represents us,... and we and this contest represent our club. Joining us on the problem-setting panel ...

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AtCoder Beginner Contest 262 Announcement We will hold AtCoder Beginner Contest 262. - Contest URL: https://atcoder.jp/contests/abc262 - Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20220731T2100&p1=248 - Duration: 100 minutes - Number of Tasks: 8 - Writer: [user:m_99,2022-07-30], [user:KoDaman,2022-07-30], kyopro_friends, [user:leaf1415,2022-07-30], [user:PCTprobability,2022-07-30], [user:nok0,2022-07-30] - Tester: [user:PCTprobability,2022-07-30], [user:physics0523,2022-07-30] - Rated range: ~ 1999 The point values will be 100-200-300-400-500-500-600-600. Since this is used as a qualification round of a local contest, - Earlier problems are easy to implement. - Later problems have similar difficulties. - The style of problems are slightly different (though closer to normal ABCs than to normal ARCs). We are looking forward to your participation!

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Invitation to TOKI Open Contest March 2018 Hello Codeforces Community, TOKI Open Contest is back again! :D We would like to invite you to participate in this TOKI Open Contest March 2018. TOKI Open Contest is Indonesian (bi-)monthly online programming contest. You may see the January 2018 contest [here](http://codeforces.me/blog/entry/57280)! :) Every problem is written in both Bahasa Indonesia and English. The contest will be divided into **two divisions**: Division 1 and Division 2. It is pretty similar to the divisions in [Atcoder](http://atcoder.jp/) (Beginner and Regular). You are free to register in any division (it's extremely OK if you are a Div2 Codeforces user and register to our Division 1 contest)! The expected difficulties of the problems are much the same with Atcoder's contest problems. TOKI Open Contest March 2018 will be held on [Saturday, 24 March 2018, 19.00 — 21.00 Western Indonesian Time (UTC+7)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=TOKI+Open+Contest+March+2018&iso=20180324T19...

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Second edition of Marathon24 team programming contest Hello everyone!  Once again we invite you to participate in the 24-hour team programming contest **Asseco Programming Marathon24 Gdynia 2014. Powered by CodiLime**. The first edition in 2013 was quite a success: 243 teams of three from over 20 different countries were registered for the contest and 30 teams from 8 countries were qualified for [the finals in Gdynia](http://marathon24.com/gallery/2013/#video). In the contest teams of three can participate. There is no limit concerning the age or education of contestants. Also there is no limit in equipment, programming languages or materials you can use during the contest. The contest consists of two stages. You can check out [problems from the first edition](http://marathon24.com/archive/2013/#qualifications) to familiarize yourself with the format. This year's tasks will also be prepared (among others) by Tomasz Idziaszek [user:monsoon,2014-09-23] and Wojtek N...

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Creating AI Bot — Code a la Mode by Codingame Hi. [https://www.codingame.com/](https://www.codingame.com/) regularly holds 10-day long competitions where you should write a program that plays a 2-player game. Sometimes you must move units/soldiers in a grid, sometimes it's a card game. The next game starts tomorrow (Friday) and then we'll see what's the topic (well, it must be food related).  I'm going to stream my approach from scratch on [Youtube](https://www.youtube.com/watch?v=RvqcuKLqQyI) and [Twitch](https://www.twitch.tv/errichto). Start on Friday at [9pm CET](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Code+a+la+mode+-+AI+bot+stream&iso=20190308T21&p1=262&ah=2) (3pm EST). Btw. I streamed the previous game three months ago, [link](https://www.youtube.com/watch?v=wWvkJZMlg8U). No prerequisites needed. I will explain my thoughts and give general advice for this type of contests. Feel free to ask questions in chat. See you...

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Huawei IOI/EGOI/CEOI/etc. Camp 2025 [registration started] - [2022 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH) &mdash; CEOI 2016, CEOI 2017, CEOI 2022, optimization problems, segment tree nodes - [2023 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eAN_QrR5MKnaZROHVSCaQiL) &mdash; POI 2019, POI 2022, CEOI 2018, graphs - [2024 recordings](https://www.youtube.com/playlist?list=PLg_Krngrs0eCfvefczNWB-c-Af3BUSH0x) &mdash; POI 2016, POI 2019 mix, POI 2023, IOI 2014, lazy propagation, sweep line, partial dp/bfs (Bombs) Hi! For a fourth time, I'm organizing an online IOI camp sponsored by Huawei. It's free for IOI participants and coaches. **UPDATE**: we will accept participants of regional olympiads too (from this year, so e.g. BOI/EGOI/CEOI/APIO 2025)! Every day will be a 5-hour virtual contest, the problem analysis, and sometimes a lecture. - Dates: 17-23.07 (6 training days; Sunday off) - Contests: IOI 2015, POI 2024 and something else from POI/BOI/CEOI - **[EDIT]** Registration: Y...

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New team programming contest: Marathon24 Hello everyone!  We invite you to participate in a new team programming contest **Asseco Programming Marathon24 Gdynia 2013**. In the contest teams of three can participate. There is no limit concerning the age or education of contestants. Also there is no limit in equipment, programming languages or materials you can use during the contest. The contest consists of two stages. If you have participated in Challenge24, you should be more or less familiar with the format. The first stage are qualifications, which will start on [19th October 2013 at 9:00 CEST](http://www.timeanddate.com/worldclock/fixedtime.html?msg=Marathon24+Qualifications&iso=20131019T09&p1=262&ah=5) and will last for 5 hours. There will be 5 algorithmic problems, to which 10 test cases will be provided. You only submit outputs to the tests and you get immediate feedback on your score. Some problems will have only one answer, and some will be optimiz...

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Useless CP Information #8: Are LGMs Overrated? Alright, clickbait title aside, how do tourist and jiangly get to 4000 rating? In chess, real life ratings cap out at around 2900, and even on online sites like Lichess, [the highest bullet players are 3300-3400, and just around 3000 for the other modes](https://lichess.org/player). Also, anecdotally, if rating is correct, the model predicts that someone who is 2940 should beat me 99.1% of the time. I have a gut feeling I beat more than 0.9% of GMs and LGMs in round 1105 and round 1108. <spoiler summary="Review on rating models if you forgot"> Rating represents win probability. In a match, for every 400 points player A is rated higher than player B, player A is 10 times more likely to win (exponentially). - If player A is rated 400 points higher than player B, then out of 11 games, player A should win 10 and player B should win 1. - If player A is rated 800 points higher than player B, then out of 101 games, player A should win 100 and player B should win 1. This can be ...

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Haskell solutions For those who are interested, here is a list of all problems for which Haskell solutions have been submitted. (Use the 'Status filter' to show only the Haskell submissions.) [1A](http://codeforces.me/problemset/status/1/problem/A) [1B](http://codeforces.me/problemset/status/1/problem/B) [1C](http://codeforces.me/problemset/status/1/problem/C) [2A](http://codeforces.me/problemset/status/2/problem/A) [2B](http://codeforces.me/problemset/status/2/problem/B) [2C](http://codeforces.me/problemset/status/2/problem/C) [3A](http://codeforces.me/problemset/status/3/problem/A) [3B](http://codeforces.me/problemset/status/3/problem/B) [3C](http://codeforces.me/problemset/status/3/problem/C) [3D](http://codeforces.me/problemset/status/3/problem/D) [4A](http://codeforces.me/problemset/status/4/problem/A) [4B](http://codeforces.me/problemset/status/4/problem/B) [4C](http://codeforces.me/problemset/status/4/problem/C) [4D](http://codeforces.me/problemset/status/4/problem/D)...

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Contest #1 — Editorial ## Introduction Contest #1 was an exciting competition with strong participation from multiple contestants. The contest featured four problems (A, B, C1, C2), and the results were as follows: [user:EyadBT,2025-03-03] achieved the first accepted solution in A, C1, and C2. [user:Ibrahimfostok,2025-03-03] was the first to solve B. The fastest full completion was achieved by [user:EyadBT,2025-03-03] (67 minutes). --- ## Standings | Rank | User | Solved | Penalty | |------|------|--------|---------| | 1 | [user:EyadBT,2025-03-03] | 4 | 67 | | 2 | [user:MoamenZ,2025-03-03] | 4 | 118 | | 3 | [user:Mazen_Ghanayem,2025-03-03] | 4 | 134 | | 4 | [user:sword060,2025-03-03] | 4 | 203 | | 5 | [user:AhmedElseyoufi,2025-03-03] | 4 | 207 | | 6 | [user:mostafaabdelaal_03,2025-03-03] | 4 | 229 | | 7 | [user:ALFarouK,2025-03-03] | 4 | 253 | | 8 | [user:Ibrahimfostok,2025-03-03] | 4 | 261 | | 9 | [user:AliRagab313,2025-03-03] | 4 | 262 | | 10 | [user:AL70SSAIN,2025-03-03] | 4 | ...

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My Facebook page about algo & Monday CF stream! If you use Facebook, you might want to check out my new page [https://www.facebook.com/errichto](https://www.facebook.com/errichto). I will post some short problems, puzzles I know/heard (maybe also not-algo puzzles, who knows), mention upcoming contests or cool problems from recent ones, sometimes share my thoughts about an algorithm or a contest. Kind of a blog, but likely with shorter but more frequent posts. Cheers! PS. next Competitive Programming stream will be on Monday, div2 C-D problems from recent CF rounds, [12pm CEST](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Errichto+Stream+22.10&iso=20181022T12&p1=262).

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Python Codeforces API Wrapper library Hi there! I would like to introduce wrapper [library](https://github.com/soon/CodeforcesAPI) for Codeforces API written in Python 3. It helps you with collecting, analyzing and visualizing data. ####Intro: As a contest member you may want to increase your power by solving problems, but some of them are quite simple, and you want to skip them. Lets say, you want to practice only Div2-C problems. You could, of course, open Problemset, then press `Ctrl+F` and write `C` to highlight preferable problems. But this may take a long time (you should look through the page and open only unsolved Div2 problems. A little boring, neh?). Another way is write a script for loading all problems then filter only unsolved Div2-C problems and sort by solved count. Sounds interesting, isn't it? There is an [example](https://github.com/soon/CodeforcesAPI/blob/examples/examples/show_only_unsolved_problems/main.py) of such script. All you need is run it and input your codeforces handle, and it w...

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AtCoder DP Stream Hi. On Sunday, I'm going to solve problems from the Educational Dynamic Programming contest on AtCoder &mdash; [https://atcoder.jp/contests/dp](https://atcoder.jp/contests/dp). Start at 10:00 CET ([check your timezone] (https://www.timeanddate.com/worldclock/fixedtime.html?msg=AtCoder+DP+stream&iso=20190217T10&p1=262&ah=5)), expected duration 5 hours. Watch me on YT or Twitch: [https://www.youtube.com/errichto](https://www.youtube.com/errichto), [https://www.twitch.tv/errichto](https://www.twitch.tv/errichto). There will be 26 problems, all on dynamic programming. More info [here](https://codeforces.me/blog/entry/64250). See you tomorrow!

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ICPC Streams/Screencasts (Swiss Subregional 2019, Petrozavodsk) I and [user:Radewoosh,2021-01-26] will virtually participate in Swiss-Slovak subregional ([announcement](https://codeforces.me/blog/entry/70777), [contest](https://codeforces.me/contestInvitation/47b8fb8b3fd6adb70dbc4d8c1f2a413587fafae9)) on Tuesday at [16:00 CET](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20210126T16&p1=262&ah=5). Watch my live stream on Twitch https://www.twitch.tv/errichto. Or later rewatch on YT https://youtu.be/M-xGjXwTXzQ. Thanks to [user:Xellos,2021-01-26] for the suggestion and [user:majk,2021-01-26] for the contest. This should be a nice warm-up before Petrozavodsk camp, which starts in a few days. I'm going to participate in half of the contests (as a member of mixed Polish Mafia team). I will record screencasts if allowed.

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Codingame Xmas — creating AI bot, stream Wednesday evening ([check your time zone](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Codingame+Xmas&iso=20181212T17&p1=262&ah=3)) I will stream solving an AI bot problem on Codingame, [https://www.codingame.com/ide/challenge/xmas-rush](https://www.codingame.com/ide/challenge/xmas-rush). As usually, I will talk a lot about what I'm doing. The goal is to show you how to approach this kind of problems. Link to the stream on Youtube (and currently just the countdown): [link](https://www.youtube.com/watch?v=wWvkJZMlg8U).  If you want to chat with me before or after the stream, visit the Competitive Programming discord, [link](https://discordapp.com/invite/UzaURu7).

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Kickstart & Leetcode live stream (post-contest) There are two mainstream contests tomorrow (Google Kickstart and Leetcode biweekly) and I will make a live stream just after them at [18:30 CEST on Saturday](https://www.timeanddate.com/worldclock/fixedtime.html?iso=20191019T1830&p1=262). After talking about some problems from those contests, I will upsolve Codeforces or Topcoder problems, maybe from a recent CF round by tourist. Watch me on Youtube &mdash; [https://youtu.be/w3W-w0EXEtc](https://youtu.be/w3W-w0EXEtc).

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Подготовься к респе::третья неделя Привет, Codeforces! Немного поменял свой план, чтобы лучше подстроиться под то, что нужно. А именно: меньше решал задачи, больше разбирал темы. Итак, итоги: - MWJ: Был в Div. C, по итогу вошёл в топ-5. По олимпиаде заключительного дня также получил 3 дип. В целом, мне эти сборы очень понравились, извлёк для себя много нового. Разобрался наконец-то с тем, как работает суффиксный автомат, потоки. Если у вас будет возможность участвовать в следующем году &mdash; очень советую. Спасибо большое [user:snarknews,2022-03-07] за организацию такого интересного формата сборов! <img src="/predownloaded/22/da/22da511fd89bf54a6bb16ac04cc3e45e8ce8209d.jpeg" style="width:35%"/> - Вторая половина недели: разбирал темы, которые могут потом пригодиться. Решил свою первую задачу на [<font style="color:#006400">Центроидную декомпозицию</font>](https://codeforces.me/contest/161/submission/148051923), [<font style="color:#006400"> Метод отжига </font>](https://codeforces.me/contest/745/submi...

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Google Hash Code Warm-up Stream [At 18:00 CET on Saturday](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Hash+Code+Warm-up&iso=20200215T18&p1=262), as a warm-up before [Google Hash Code](https://hashcode.withgoogle.com/) qualification round, I will solve a practice problem (or just some old problem?) live together with my teammate [user:kabuszki,2020-02-15]. You can watch us on YT or Twitch https://www.youtube.com/errichto2/live & https://www.twitch.tv/errichto. I know it collides with SRM but this time is convenient for me. Maybe I will also record our qualification round performance on Thursday, we'll see. Unrelated: expect a few short problem-solving streams next week, stay tuned.

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Invitation to RookieRank on HackerRank Hello everyone,  I'm pleased to invite you, especially these ones of you who are starting with competitive programming, or like to practice with easy problems, to compete in a brand new contest RookieRank by HackerRank: [https://www.hackerrank.com/rookierank](https://www.hackerrank.com/rookierank) The contests starts in 4 hours ([July 26 2016 at 6PM CET](http://www.timeanddate.com/worldclock/fixedtime.html?msg=%5BHackerRank%5D+RookieRank&iso=20160728T18&p1=262)), and there will be 5 problems to solve, starting from very easy ones up to a few just slightly harder. I'm the author of 4 of them. Moreover, there will be two separated leaderboards. One especially for all first time competitive programmers, i.e. these who are not listed on the Algorithms Leaderboard yet. The point is, that if you are just starting on HackerRank, you will compete with other people with similar experience. ...

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Who participated most? This is top100 with most participated in official contests, included non-rated ones. |Rank|Handle|Total|Official|Unofficial| |---|---|---|---|---| | 1 |  [user:ruban,2019-12-23] | 660 | 612 | 48 | | 2 |  [user:PAG,2019-12-23] | 604 | 585 | 19 | | 3 |  [user:uwi,2019-12-23] | 587 | 352 | 235 | | 4 |  [user:dreamoon_love_AA,2019-12-23] | 511 | 351 | 160 | | 5 |  [user:kmjp,2019-12-23] | 506 | 319 | 187 | | 6 |  [user:KrK,2019-12-23] | 471 | 314 | 157 | | 7 |  [user:2-SAD,2019-12-23] | 458 | 311 | 147 | | 8 | ![ ](https://sta.codeforces.com/s/5...

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SICK MINDS !!!! Codeforces Round #262 (Div. 2) : all these new accounts just registered in codeforces before 29 hour ago except "Memset137" : [user:6wr1,2014-08-20] [user:shaojj,2014-08-20] [user:poaspoas1,2014-08-20] [user:girlfriends,2014-08-20] [user:Nyaruko,2014-08-20] [user:kiss_me,2014-08-20] [user:KingTon,2014-08-20] [user:Memset137,2014-08-20] [user:GFW_sb,2014-08-20] [user:prathyu,2014-08-20] maybe i am wrong but it is obvious that they are Div1 participants depending on what they solve !! now if we eliminate these participants we will get the TRUE standing . 1 &mdash; [user:buptcjj,2014-08-20] 2 &mdash; [user:ladvnlt,2014-08-20] 3 &mdash; [user:linjek,2014-08-20] 4 &mdash; [user:AmrMahmoud,2014-08-20] 5 &mdash; [user:rureggaeton,2014-08-20] 6 &mdash; [user:win_ay39,2014-08-20] 7 &mdash; [user:ErdemKirez,2014-08-20] why they do this ?!! they can participate even if they are Div1 !

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Judge returning a different answer from local testing. Hello, in short, I'm trying to solve [problem:1999E] with the following solution: [submission:276991813] While testing locally, the solution correctly returns the expected output for the sample test case, but the judge says the following: "wrong answer 4th numbers differ &mdash; expected: '263', found: '262' " I tried some online compilers and they also return the expected output with my solution. Why is the judge returning a different output?? Any help would be appreciated, thanks.

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IOI 2023 Country Standings Hello everyone! Similar to [last year](https://codeforces.me/blog/entry/105957), these are the country standings for IOI 2023 based on the sum of scores of all contestants. Check the spoiler at the bottom for the complete list. <table style="width:100%"> <tr> <th>Rank</th> <th>Team</th> <th>Score</th> </tr> <tr> <td>1</td><td>CHN</td><td>1997.5</td></tr> <tr> <td>2</td><td>USA</td><td>1624.5</td></tr> <tr> <td>3</td><td>JPN</td><td>1574</td></tr> <tr> <td>4</td><td>IOI_2</td><td>1463.5</td></tr> <tr> <td>5</td><td>TWN</td><td>1296</td></tr> <tr> <td>6</td><td>KOR</td><td>1218.5</td></tr> <tr> <td>7</td><td>POL</td><td>1201.5</td></tr> <tr> <td>8</td><td>ISR</td><td>1187.5</td></tr> <tr> <td>9</td><td>CAN</td><td>1168</td></tr> <tr> <td>10</td><td>VNM</td><td>1129.5</td></tr> </table> <spoiler summary="Complete list"> <table style="width:100%"> <tr> <th>Rank</th> <th>Team</th> <th>Score</th> </tr> <tr> <td>1</td><td>CHN</td>...

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Contests hack statistics (Number of hacks by round) Just felt like gathering some data about hacks. Parsed around ~400 last contests Probably it would be worth it to also include SFT, but whatever Educational 96 is not finished yet but also whatever Last 100 ------------------ **847** Educational Codeforces Round 96 (Rated for Div. 2) **30** Codeforces Global Round 11 **248** Codeforces Round #674 (Div. 3) **0** 2020 ICPC, COMPFEST 12, Indonesia Multi-Provincial Contest (Unrated, Online Mirror, ICPC Rules, Teams Preferred) **97** Bubble Cup 13 &mdash; Finals [Online Mirror, unrated, Div. 2] **86** Bubble Cup 13 &mdash; Finals [Online Mirror, unrated, Div. 1] **20** Codeforces Round #675 (Div. 2) **1** Codeforces Round #672 (Div. 2) **70** Codeforces Round #671 (Div. 2) **58** Educational Codeforces Round 95 (Rated for Div. 2) **3** Codeforces Round #673 (Div. 2) **11** Codeforces Round #673 (Div. 1) **73** Codeforces Round #667 (Div. 3) **121** Grakn Forces 2020 **4** Co...

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Республиканская олимпиада 2022 год. Казахстан 2021 : https://codeforces.me/blog/entry/90111 2020 : https://codeforces.me/blog/entry/80808 2019 : https://scoreboard.bc-pf.org/results/informatics/national-olympiad/2019 2018 : https://codeforces.me/blog/entry/58432 2017 : https://codeforces.me/blog/entry/51416 #### 9 класс <table> <thead> <tr> <th>Место</th> <th>ФИО</th> <th>CF handle</th> <th>Балл</th> <th>Медаль</th> </tr> </thead> <tr> <td>1 </td><td>Таймас Мансур</td><td>[user:gamicrab,2022-04-19]</td><td>322</td></td><td><img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a72d9e.png" style="max-width: 100.0%;max-height: 100.0%;"> </td> </tr> <tr> <td>2 </td><td>Абжами Ерсултан</td><td>[user:syrtin,2022-04-19]</td><td>274</td></td><td><img alt=" " src="/predownloaded/93/73/9373156f429b185ba6bc779f81d16894f9a72d9e.png" style="max-width: 100.0%;max-height: 100.0%;"> </td> </tr> <tr> <td>3 </td><td>Шермаханов Ильяс</td><td>[user:Tenjin,2...

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Ubuntu Algorithm Classes Hello, On Friday, April 13 17:00 UTC[1], at channel #ubuntu-classroom (freenode.net server) the first workshop Ubuntu Algorithm Classes are held, which are dedicated to the practical application of the algorithms in programming. I invite everyone, especially beginners, to participate. Workshops have their own online judge system, which now includes the tasks. I encourage you to exercise, the workshops are simple and focused on learning specific methods / algorithms. Online judge: http://onlinejudge.xn.pl Notes can be found at: https://docs.google.com/document/d/1CHU5TgXegp6IkRQhx7ok9HFNMPVONiWojbkIgfdFJrQ/edit For more information, visit: http://bdfhjk.blog.pl [1]http://www.timeanddate.com/worldclock/fixedtime.html?msg=Algorithm+Classes&iso=20120413T19&p1=262&ah=1 Marek Bardoński

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Задачи А на контестах Good Bye 2013 и Codeforces Round #262 Вот [это](http://codeforces.me/contest/379/submission/5572013) мое решение задачи А на контесте Good Bye 2013. Если этот код сдать **вообще** без изменений [сюда](http://codeforces.me/problemset/problem/460/A)(это задача А с Codeforces Round 262(div. 2)), то решение получает АС. Это уже как-то слишком... **upd:** переименовал пост

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

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Республиканская олимпиада 2021 года. Казахcтан. Результаты. 2021 : https://codeforces.me/blog/entry/90111 2020 : https://codeforces.me/blog/entry/80808 2019 : https://respa.daryn.kz/ 2018 : https://codeforces.me/blog/entry/58432 2017: https://codeforces.me/blog/entry/51416 ####9 Класс <html> <body> <style type="text/css"> .tg {border-collapse:collapse;border-spacing:0;} .tg td{border-color:black;border-style:solid;border-width:1px;font-family:Arial, sans-serif;font-size:14px; overflow:hidden;padding:10px 5px;word-break:normal;} .tg th{border-color:black;border-style:solid;border-width:1px;font-family:Arial, sans-serif;font-size:14px; font-weight:normal;overflow:hidden;padding:10px 5px;word-break:normal;} .tg .tg-0pky{border-color:inherit;text-align:left;vertical-align:top} </style> <table class="tg" style="undefined;table-layout: fixed; width: 579px"> <colgroup> <col style="width: 50px"> <col style="width: 160px"> <col style="width: 170px"> <col style="width: 97px"> <col style="width: 102px"> </colgroup...

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codeforces round 262 http://codeforces.me/contest/460/problem/C can any one pls explain how to do this problem through binary search. #include <iostream> #include <stdio.h> using namespace std; long long i,n,k,m[200010],w,l,r,z,a[200010],kol,sum,p; int main(){ //freopen("input.txt","r",stdin); //freopen("output.txt","w",stdout); cin>>n>>k>>w; for (i=0;i<n;i++) cin>>m[i]; l=1; r=10; while (l<=r){ z=(l+r)/2; kol=0; sum=0; for(p=0;p<10;p++) a[p]=0; for ( i=0;i<n && kol<=k;i++){ sum=sum+a[i]; if (m[i]+sum<z){ kol=kol+z-(m[i]+sum); a[i+w]-=z-(m[i]+sum); sum=z-m[i]; } } if (kol<=k) l=z+1; else r=z-1; } cout<<r; return 0; } here is one of the codes and i couldnt understand any thing at all.

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

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codeforces round 262 could any one pls explain the following problem clearly so that a beginner could understand http://codeforces.me/contest/460/problem/C

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First Ever Users to Reach Some Rating Milestones Revised: ratings above 1500 and greatest falls Several days ago I published a [table](https://codeforces.me/blog/entry/104320) with first people to reach certain ratings. It was a bit raw because, firstly, it was based on top 20000 Codeforces users by rating, and, secondly, because it only gave information about ratings divisible by 50. Now I have prepared a table that is of more complex design, but both issues are resolved. Good luck understanding what is going on in it. [cut] For several reasons I firstly put another table. This is the table of greatest rating falls in the history of Codeforces. The reasons are: 1. I have collected so much data from Codeforces that it would be blasphemy not to use it in as many ways as possible. 2. These tables might intersect a lot: it's easier to get a terrific fall in ratings if you are high-rated. 3. Someone recently posted a table with greatest rating rises and falls. I wasn't able to find this table to check whether it was right, but if someone finds it, you're welcome to pu...

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

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

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Milestones: ratings below 1500 and greatest rises (2024 edition) <i>Note.</i> This is an updated version of [this post](https://codeforces.me/blog/entry/104683). If you like [this style](https://codeforces.me/blog/entry/104320) more, please tell me in the comments. Since [user:tourist,2024-09-05]'s [breakthrough](https://codeforces.me/blog/entry/133401), I've received a lot of requests to update my old posts with rating achievements. However, I wasn't able to do it immediately since my method of doing it requires to download the rating change history of every user, which, in turn, requires to perform several hundred thousand requests to Codeforces, about which the website (and Cloudflare) is not happy. It took more that three days, but finally the job is done! Below are two tables. The first one is the greatest positive rating changes. The second one is the first users ever to reach some rating value. [cut] <table> <tr> <th>Place</th> <th>&Delta;</th> <th>Person</th> </tr> <tr> <td>1^st</td> <td><b>1182<...

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