OCPC 2025 Winter — wrap Hi everyone! <center><a href="https://ocpc.camp"><img src="https://ocpc.camp/images/ocpc.svg" height="100px"></a> <a href="https://icpc.foundation/"><img src="/predownloaded/43/08/43086529a28ccb5c9f2f2eec560ffa85e09c6881.svg" height="100px"></a></center> <center> <b>Supported by</b><br> <a href="https://www.quantco.com/"><img src="https://ocpc.camp/images/quantco.svg" height="60px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://ordercapital.com/"> <img src="https://ocpc.camp/images/OrCa.svg" height="60px" style="margin: 10px 10px 10px 10px;"> </a> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="60px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="60px" style="margin: 10px 10px 10px 10px;"></a> </ce...

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OCPC 2024 Winter — wrap Hi everyone! <center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a> <a href="https://icpc.foundation/"><img src="https://ocpc.mathos.unios.hr/images/ICPC.svg" height="100px"></a></center> <center> <b>Sponsored by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="50px" style="margin: 5px 5px 5px 5px;"></a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="50px" style="margin: 5px 5px 5px 5px;"></a> </center> Yesterday marked the conclusion of the third [Osijek camp](https://ocpc.mathos.unios.hr) (also see the [announcement](https://codeforces.me/blog/entry/124573) on Codeforces). Similar to the last time, the camp was organized by Tähvend Uustalu ([user:-is-this-fft-,2024-02-26]) and m...

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OCPC 2026 Winter — wrap _If you are potentially interested in participating in OCPC **in person** in Summer/Autumn 2026, **please** fill **[this form](https://forms.gle/VdMRh6cAJRN4YvQN6)**!_ Hi everyone! <center><a href="https://ocpc.camp"><img src="https://ocpc.camp/images/ocpc_light.svg" height="80px"></a> <a href="https://icpc.foundation/"><img src="/predownloaded/43/08/43086529a28ccb5c9f2f2eec560ffa85e09c6881.svg" height="80px"></a></center> <center> <b>Supported by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="40px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://www.hudsonrivertrading.com/"> <img src="https://ocpc.camp/images/HRT.svg" height="40px" style="margin: 10px 10px 10px 10px;"></a> <a href="https://www.silares.com/"> <img src="https://ocpc.camp/images/silares-red.svg" height="40px" style="margin: 10px 10px 10px ...

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Osijek Competitive Programming Camp 2023 fall — wrap Hi everyone! <center><a href="https://ocpc.mathos.unios.hr"><img src="https://ocpc.mathos.unios.hr/images/ocpc.svg" height="100px"></a></center> <center> <b>Supported by</b><br> <a href="https://www.janestreet.com/join-jane-street/open-roles/?type=students-and-new-grads&location=london"> <img src="/predownloaded/ee/f2/eef26616a3661c658d1545f18ed21fabb14d5871.svg" height="50px" style="margin: 5px 5px 5px 5px;"></a> <a href="https://icpc.foundation/"><img src="https://ocpc.mathos.unios.hr/images/ICPC.svg" height="70px" style="margin: 5px 5px 5px 5px;"></a> <a href="https://pinely.com/"> <img src="/predownloaded/0a/0f/0a0f3f67435d1f6e467bc7203d4a2090ba8f92cc.svg" height="50px" style="margin: 5px 5px 5px 5px;"></a><br> <a href="https://artofproblemsolving.com/"><img src="https://ocpc.mathos.unios.hr/images/aops.svg" height="40px" style="margin: 5px 5px 5px 5px;"></a> <a href="https://www.wolfram.com/"> <img src="https://ocpc.mathos.unios.hr/images/wolfram.png" height="40...

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Looking for people for escape room in San Jose I want to go to Joker's Asylum ER in San Jose (California) on the 7th of August, two days before GCJ finals. It's a difficult escape room and a team should consist of 5-10 people. So far, there's me and my friend &mdash; not really pros. I'm looking for more people to go there and maybe grab a beer later. If the date is fine for you and you are good at ER and/or algo, write a DM to me. This room has very good reviews and the escape room veteran [user:Swistakk,2019-07-12] recommends it a lot. Sounds promising, right?

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I was in a room of CHEATERS! In [contest:2002], I failed to solve D2 and got -29, and look at the room I'm in! Pupil and specialist were extremely good at coding and they won ratings from naive CMs just like me!  [user:ravikatharotiya392,2024-08-12] failed system test on A, and this is what he submitted [submission:275770575], and needless to say, 100% a cheater. And he had a skipped contest just a week ago. [user:klu-2100030642cser,2024-08-12], converted his code to GO, perl, php with ChatGPT to escape plagiarism check. [submission:275842762] [submission:275793939] And I'm pretty scared to see that he hasn't been caught even once in his 16 rated contests, he was a really clever cheater!!! Just in one room two cheaters came and defeat me so much and I can't help imagining how many cheaters are there in the whole contest! **Even problem E of Div1+2 can be solved by cheaters! Now cheaters can cheat their ways to Master!** There has to...

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Educational 24h livestream by me (Psyho) during the Marathon24 Some of you may read my [previous post](http://codeforces.me/blog/entry/20276). It's official now, so I can safely say that this will happen. In short: * As in title, I will be doing a 24h stream during the Marathon24. Sleeping not allowed. * [28/11 Saturday 9:15 AM GMT+1 to 29/11 Sunday 10:15 AM GMT+1](http://www.timeanddate.com/worldclock/fixedtime.html?msg=24h+Livestream+by+Psyho+during+Marathon24+finals&iso=20151128T0915&p1=3903&ah=23&am=59) &mdash; I'm starting 1 hour before the contest, that's why it's 25 hours. * I will be screencasting throughout the whole time + I will explain what and why I'm doing. The emphasis is on educational aspect. This means, that probably I won't perform too good, but at least you'll know everything that goes through my head. * My code should be available online (almost sure) + I'll maintain current TODO/schedule lists (100% sure). I'm also usually quickly writing a rich visualizer. You should be able to easily hop in at any moment and und...

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

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Codeforces Round #822 (Div.2) Editorial Thank you for your participation! [1734A &mdash; Select Three Sticks](https://codeforces.me/contest/1734/problem/A) ------------------ We first sort the array $a$ in non-decreasing order. Denote the indices of the elements that we choose from $a$ to be $x$, $y$, and $z$, where $1 \le x < y < z \le n$, and the final value (after performing the operations) of the concerned elements to be $v$. The minimum required number of operations is then $|a_x-v|+|a_y-v|+|a_z-v|$. It is well-known that such expression attains its minimum value when $v$ is the median of $a_x$, $a_y$, and $a_z$. Since the array $a$ has already been sorted, it is best to assign $v$ to be $a_y$. Our expression then becomes $|a_x-a_y|+|a_y-a_y|+|a_z-a_y|=(a_y-a_x)+0+(a_z-a_y)=a_z-a_x$. We would like to minimize the value of $a_z$, which implies $z$ should be as small as possible since $a$ is sorted. It is clear that taking $z=y+1$ would minimize the value of the expression. Similarly, we can show that we ...

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Some nice questions for beginners learning new stuffs (will be adding more in time) _Although I'm too a beginner but I try to learn new things everyday, so here are the questions on DS which beginners like me find hard but are too easy if learned the DS nicely._ ## Arrays | Index | Problem | Prerequisite | | --- | --- | --- | | 1 | [Maximum circular subarray sum](https://practice.geeksforgeeks.org/problems/max-circular-subarray-sum/0) | Kadane's Algorithm | | 2 | [Find subarray with given sum](https://practice.geeksforgeeks.org/problems/subarray-with-given-sum/0) | Hashing | | 3 | [Equilibrium index of an array](https://practice.geeksforgeeks.org/problems/equilibrium-point/0) | None | | 4 | [Maximum Sum Increasing Subsequence](https://practice.geeksforgeeks.org/problems/maximum-sum-increasing-subsequence/0) | Simple DP | | 5 | [K-Concatenation](https://www.codechef.com/problems/KCON) | Kadane's Algorithm | | 6 | [Convert array into Zig-Zag fashion](https://practice.geeksforgeeks.org/problems/convert-array-into-zig-zag-fashion/0) | None | | 7 | [Find...

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Ten Years of Competitive Programming 5 Hey, Codeforces! I’m AmirReza PourAkhavan, the former Codeforces Contest Coordinator. I let the story become complete, and I’m sharing it now. The story is about a 16-year-old competitive programmer who left his family and migrated to another city alone to follow competitive programming. After seven years, he advanced to the International Collegiate Programming Contest World Finals twice. Read the previous parts: [1](https://codeforces.me/blog/entry/107465), [2](https://codeforces.me/blog/entry/108838), [3](https://codeforces.me/blog/entry/114356), [4](https://codeforces.me/blog/entry/122483). **Read the Persian version** [**here**](https://docs.google.com/document/d/1TN8pnS_8te7MLDYzMjlDxFrElNVjE4ZWjo1Ak-JJdmc/edit?tab=t.isfroku1gx3e). This part covers from December 2016 to November 2017. ## The Codeforces Contest Our contest was held on Codeforces, and it broke several records. - The record for the highest number of upvotes on an editorial. - The record f...

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Problems that I authored so far **UPD 1 [May 17 2025]:** I added my problems from Ukrainian Olympiad in Informatics (among others). They are available here: [contest:105820] Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs [by](https://codeforces.me/blog/entry/108940) [user:adamant,2023-02-20] and [by](https://codeforces.me/blog/entry/108595) [user:tibinyte,2023-02-20]; I finally decided to do it after my Universal Cup contest. This is not a super-comprehensive list, I also set some problems for some local contests, but that's most of it. I want to encourage other setters to write such blogs. For me, it's very interesting to read about the backstories of some problems and also to see all the problems by some author gathered in one place (as most authors give problems to several platforms). One important point. As you will see from the comments, many of my problems were improved by other people, and I myself improved some problems by other people. I think that it's cruc...

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BFS PROBLEMS Yesterday I read BFS for first time. I knew before DFS,and I had use it in 10+ problems,so it was a bit easier to undestand BFS. After of much time of reading(editorial) and effort,I undestood the solution of this: "Inviational 02 Semifinal Room 2 &mdash; Div 1 500 &mdash; Escape",problem from topcoder,and I solved it. But I saw that in topcoder tutorial,has not other bfs problems. Could you link me one more BFS problem down,that his difficulty is almost same with the above problem? (I googled it,but in my results,I did not find the level of each problem,so I couldnt know,if I am suitable to solve that.) Thank you for your time, and sorry if my english is a bit meaningless :P !!!

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A2SV Remote G5 — Contest #25 Editorial [Here](https://codeforces.me/contests/537575) is the link to the contest. Provide your feedback on each problem so that we can improve upon them the next time. [A. Valid Parentheses](https://codeforces.me/gym/537575/problem/A) ------------------------------------------------------------------- <spoiler summary="Solution"> The most optimal length is achieved if no parentheses need to be removed, but sometimes parentheses must be removed to maintain the balanced property. This happens when encountering a <b>)</b> before a matching <b>(</b>. To solve this, traverse the string from left to right. Every time you encounter a <b>(</b>, increment the open parentheses count by one. If you encounter a <b>)</b>, the count of open parentheses must be at least one. If it is, decrement the count by one and increment your result by two (one for the <b>(</b> and one for the <b>)</b> because both are part of the remaining valid string). If not, it means you have to remove this closing paren...

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

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