Bay Area Programming Contest 2022 ### About The Bay Area Programming Contest, a programming contest for precollege students, will be held on June 12 from 10 am to 2 pm PDT. **Note that the contest has been pushed back by 1 hour to avoid colliding with Educational Round 130**. You can check the converted time [here](https://www.timeanddate.com/worldclock/fixedtime.html?msg=BAPC+2022&iso=20220612T10&p1=1240). If you are not a precollege student, you can participate, but you will not be eligible for prizes. The problems were created by [user:EndlessVoid,2022-06-11], [user:GusterGoose27,2022-06-11], [user:pocafup,2022-06-11], [user:lce4113,2022-06-11], and [user:NightWizard777,2022-06-11]. Problem preparation was done by [user:BucketPotato,2022-06-11]. Additional thanks to [user:eggag32,2022-06-11] and [user:izhang,2022-06-11] for testing the problems. ### Logistics The contest will be conducted through our [Codeforces group](https://codeforces.me/group/5kleZAqa52). Only those who fill out the registration for...

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IIOT — Open Contests 2021/2022 — Final Round Winners Announcement The final round of IIOT took place last weekend and we would like to thank all the teams who participated. The problems were harder than usual, the hardest being police7, which only had 2 teams get a full score on it. In the onsite contest, calculator, colorpoints, police7 and prankster were not solved completely by any team. Now, on with the top 5 teams: - In the fifth place, team "DB_Fanclub ><", from India, with 634 points. - In the fourth place, team "aa bb", from Italy, with 700 points. - In the third place, team "Alon Tanay", from Israel, with 735.83 points. - In the second place, team "pave ment", from Singapore, with 744.1 points. And finally "Bushido Staszic", from Poland, came first with a full score. Congratulations to all! The full ranking is available [here](https://mirror.squadre.olinfo.it/ranking/). Tommaso Dossi (on behalf of the Italian IIOT organizers)

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Ten Years of Competitive Programming 4 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 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). **Read the Persian version** [**here**](https://docs.google.com/document/d/e/2PACX-1vSUoFC9tLgDCji6rSCYy-RYoUG1_6uOQnHz_LlLKe6KksWBYWO4r6clDly5YxIgzu1g3Tj31weDxgWz/pub). What happened previously === I was a lone programmer, in a small city, trying to learn CP and prepare for the Iran National Olympiad. It was not as successful as I expected. I tried to change my school and I immigrated to Tehran, alone. I entered AE high s...

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Virtual Participation || Score Calculator **Hi,**<br> I've planned to concentrate on speed up solving problems A, B and C recently. So I need to solve just these problems, not all the problems of a round and evaluate my performance according to the scores (for each problem) that I've taken.<br> In order to do this, I thought about something like virtual participation; But I noticed that, I can have at most 1 virtual participation for each round, and because of I will have the same practice plan for D and E problems in the future, I don't want to do that!<br> Is there any other options for me (on Codeforces or other websites) to do this kind of practice?<br> What about a tool for calculating the scores (Score Calculator)? Is there? **Thanks..**

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1/phi Halving in Interactive Tree Problems Thanks to [user:toxicpie9,2025-04-22] for proofreading and emotional support. Recently, I was thinking about JOISC 2025 Space Thief. And there is a part where you need to do divide and conquer on a tree, where you need to split the edges of the tree into two components where the edges are both connected. Basically, we consider an interactive problem on a tree where there is a hidden edge. We are allowed to ask queries of the form $(v,N_v)$ where $v$ is a vertex of the tree and $N_v$ is a set of neighbouring edges of $v$. Then the query returns to us whether the hidden edge is in the subtree of one of $N_v$ when we root the tree at $v$. We maintain a set of edges that the hidden edge can be in. In each query, we try to split the set of edges into two parts and ask a query to separate them. In the worst case, we replace the set of edges by the larger component. Let $R$ be the maximum ratio of the larger component. In [this blog](https://codeforces.me/blog/entry/120446)...

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Beyond the Contest: How Competitive Programming Powers Real Life and Sports If you've ever done competitive programming (CP), you know the drill — segment trees at 2 AM, dynamic programming (DP) transitions that make your head spin, graphs that refuse to be traversed efficiently. It's easy to dismiss this as "just contest stuff." But the truth is, almost every algorithm you grind on Codeforces or LeetCode has a real job somewhere in the world — and one of the most fun places to see this is sports. This post covers two things: Everyday, real-life uses of classic CP concepts. A deep dive into how algorithms — especially DP — quietly run the show in cricket, tennis, basketball, football, chess, and more. **Part 1: CP Concepts You Already Know, Working in the Real World** **** **Sorting & Searching** **** Every time you sort products by price on Amazon or search for a contact on your phone, you're using variants of merge sort, quicksort, or binary search. Databases use B-trees (a generalization of binary search trees) to fetch records in logari...

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Codeforces Round 1121 (Div. 2) Editorial # Codeforces Round 1121 — Editorial Thanks for participating! ### [problem:2264A] Problem by [user:qwexd,2026-09-13]. <spoiler summary="Hint"> Look at the elements that are not in the right position. Which of them must be selected? Can selecting any other element help? </spoiler> <spoiler summary="Solution"> Every element that is not in the right position has to be selected; otherwise, it never moves. Selecting an element that is already in the right position cannot help. For it to stay correct after the reversal, it has to be paired with itself, because its value occurs nowhere else in the permutation. Thus it can only be the middle selected element, and removing it changes nothing. So, if the array is already sorted, choose any one element. Otherwise, select exactly the misplaced elements and reverse them. The answer is `YES` if this sorts the array, and `NO` otherwise. If the misplaced positions are listed from left to right, the reversal pairs the...

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