BledDest's blog

By BledDest, 7 days ago, In English

Unfortunately, I have found out that the checker for problem E of Codeforces Educational Round 189 did not correctly verify the case when a circle does not cover any points. I am very sorry for this issue — I was not the person writing that checker, but proofreading it and fixing all of the bugs is my responsibility as the coordinator of the round, and I failed.

After discussing the issue with authors and analyzing the submissions, I have decided that dropping the constraint from the statement altogether, without any changes to verdicts during the round is the best course of action: the amount of changes in the scoreboard, compared to the situation if checker were working correctly, is negligible (perhaps even zero).

My reasoning for this

The problem statement will be updated accordingly in about $$$10$$$ or $$$15$$$ minutes.

I once again would like to apologize for not checking everything enough times, and I hope the decision I've made ensures that the minimum possible number of people are affected by this bug in checker.

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By BledDest, 8 days ago, translation, In English

2225A - A Number Between Two Others

Author: BledDest

Tutorial
Solution 1 (BledDest)
Solution 2 (BledDest)

2225B - Alternating String

Author: FelixArg

Tutorial
Solution (FelixArg)

2225C - Red-Black Pairs

Author: FelixArg

Tutorial
Solution (FelixArg)

2225D - Exceptional Segments

Author: FelixArg

Tutorial
Solution (FelixArg)

2225E - Covering Points with Circles

Author: basalov_yurij

Tutorial
Solution (FelixArg)

2225F - String Cutting

Author: FelixArg

Tutorial
Solution 1 (FelixArg)
Solution 2 (BledDest)

2225G - Simple Problem

Author: basalov_yurij

Tutorial
Solution (BledDest)

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By BledDest, history, 2 months ago, In English

Thank you for participation! We're still removing cheaters from the ranklist, so the results are not final. But we hope to finish it as soon as possible.

The problems were prepared by Neon, adedalic, Roms and me.

Huge shoutout to the testers: awoo, FelixArg and KIRIJIJI! Your feedback helped us immensely.

Now, the editorial inself:

2199A - Game

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

2199B - Two Towers

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2199C - Minesweeper

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2199D - Two Arrays

Idea: Roms, preparation: Roms

Tutorial
Solution (Roms)

2199E - Supersequence

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2199F - Self-Produced Sequences

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2199G - Jammer

Idea: adedalic, preparation: adedalic

Tutorial
Solution (adedalic)

2199H - Sum of MEX

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

2199I - Strange Process

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

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By BledDest, 2 months ago, In English

Hello Codeforces!

We are happy to announce the new episode of Kotlin Heroes! It is both an opportunity to try learning a new programming language (if you've never coded in Kotlin before) or solve programming problems of very different levels of difficulty in it (if you're already familiar with Kotlin). No matter if you're a professional or a beginner, we'll be glad to see you participate!

This is already the fourteenth time we conduct this competition, and the previous 13 episodes had lots of amazingly talented programmers participating. You can see for yourself by checking them out: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round, Episode 6, Episode 7, Episode 8, Episode 9, Episode 10, Episode 11, Episode 12 and Episode 13.

To prepare for the Episode 14, we advise you to register to the practice round, which contains several problems of various difficulties from past Codeforces contests. In the practice round, all solutions will be open to view for anyone.

We also recommend that you check some resources which can help you learn more about competitive programming in Kotlin:

And if you’d like to see how the top competitive programmers approach these challenges, check out ecnerwala and SecondThread solving problems from this practice round live on stage at the ICPC World Finals in Baku.

On March 2, 2026, the main phase of the contest starts! During Kotlin Heroes: Episode 14, you will have 2 hours and 30 minutes to solve several programming problems, ranging from simple short exercises to challenges that will test both your coding skills and algorithmic thinking.

The use of AI-based tools during the main contest is strictly limited. To find out the guidelines for proper AI use, what is allowed and what is prohibited, please read the post "Rule Restricting the use of AI". Improper use of AI tools during the main contest may result in disqualification. Using automatic translation tools (including but not limited to neural networks and AI) to convert code written in other programming languages to Kotlin goes against the spirit of the competition, so it is also strictly prohibited.

REGISTER →

Prizes:

  • 🥇 $512 (or equivalent value) for 1st place
  • 🥈 $256 for 2nd place
  • 🥉 $128 for 3rd place
  • 👕 Kotlin Heroes T-shirts for the top 50 participants
  • 🎁 A raffle of 50 T-shirts for anyone who solves at least one problem

Please note that we are not able to ship prizes to any country, state, province, or territory subject to comprehensive OFAC sanctions, including Belarus, Cuba, Iran, North Korea, Russia, Syria, or the Crimea, Donetsk, or Luhansk regions. For complete the list, please visit this page.

Good luck to all of the participants! I hope you will enjoy the problems we've prepared.

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Announcement of Kotlin Heroes: Episode 14
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By BledDest, 5 months ago, In English

Judging by the comments in the ER announcement, people seriously disliked problem D (to say the least). I want to explain why it exists.

But first, I have to admit that I made two serious mistakes when setting the problem. My first mistake is actually putting it into a 2-hour solo round; in its current state, it is much more suitable for a longer contest with a team of three people, where you can actually get some help in debugging the code or verifying your solution logic. The second mistake will be explained a bit later, but I want to say that I understand why people think this is a terrible problem. I am sorry if this problem made the contest much worse for you.

However, I am also asking that you consider my point of view. You don't have to agree with it, but I don't want anyone to view me as some insane author who's setting a problem just to watch everyone get furious while implementing it.

This is definitely an implementation-heavy problem. But I think that implementation problems should exist in contests. When people think "implementation", they usually mean one of the following two things:

  • a problem where you have to write a lot of boring code or examine a lot of corner cases;
  • a problem where you have to think a lot about your solution structure after getting its main idea, or else it will be very complicated.

I think that these are two different categories of "implementation", even if they sometimes intersect. I dislike the first type, but I think that problems of the second type can be very interesting, because they make your brain work while trying to invent an easy-to-code solution. These types of problems can be much less tedious if you don't start coding as soon as you get the general idea.

I wanted problem D to be one of the problems of the second type: not requiring any algorithms or advanced data structures, just thinking about how to implement this in the easiest way possible. However, my second mistake was not eliminating some parts of the problem which make the solution much more tedious. Like, for example, does this problem need the letter X, wouldn't it be better without it? It would be better, but unfortunately, this idea came to me only in the middle of the actual contest. Because of these small tedious parts (which don't actually add anything to the idea of the problem, not even in the implementation part), problem D shifted way closer to the first type of implementation.

I'd like to hear your thoughts on this question: if this problem had only two types of letters (only I and V, no X), would it be better? Or would it still be too much boring implementation? Why exactly this change — it's because in my opinion, letter X actually does not add anything significant to the idea of the problem, but increases the tedium way too much. Most other "implementation-heavy" parts of the problem can be made much simpler if you think about them carefully.

And to finish the post, I want to show you my thought process on solving and implementing this problem:

Solution idea + implementation ideas
My solution code

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By BledDest, 7 months ago, In English

I hope you liked the problems! Thank you for participation. I am sorry that the difference between H and I turned out to be that big, I didn't expect that so many people would solve H.

The contest was prepared by me, Neon, adedalic, FelixArg and Roms. I would like to express my gratitude to the testers who helped us improve the contest: pashka, shnirelman and awoo.

See you in the next episode of Kotlin Heroes... sometime in the future (probably near the end of 2025).

2141A - Furniture Store

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2141B - Games

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2141C - Minimum on Subarrays

Idea: FelixArg, preparation: FelixArg

Tutorial
Solution (pashka)

2141D - Avoid Minimums

Idea: BledDest, preparation: adedalic

Tutorial
Solution (adedalic)

2141E - Perfect Cut

Idea: FelixArg, preparation: Neon

Tutorial
Solution (Neon)

2141F - Array Reduction

Idea: Roms, preparation: Roms

Tutorial
Solution (pashka)

2141G - Good Robot Paths

Idea: FelixArg, preparation: FelixArg

Tutorial
Solution (pashka)

2141H - Merging Vertices in a Graph

Idea: BledDest, preparation: BledDest

Tutorial
Solution (pashka)

2141I - Color the Tree

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

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By BledDest, 8 months ago, In English

Greetings Codeforces!

Ready to put your Kotlin skills to the test? Kotlin Heroes is your playground: a chance to experiment with the language's features, tackle fun and challenging problems, and level up your programming abilities. Perfect for beginners and experts alike!

A massive shout-out to all the amazing coders who have competed in past Kotlin Heroes events: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round, Episode 6, Episode 7, Episode 8, Episode 9, Episode 10, Episode 11 and Episode 12.

Kotlin Heroes is a great way to play around with Kotlin’s features, learn something new, and practice using the language by solving fun problems. It is great for programmers of any level!

We invite you to join the practice round, where you can improve your algorithmic problem-solving skills and complete training problems. In this round, all the solutions are open, and you can request hints if you’re stuck.

Here are some things you can do to help you refresh your knowledge of Kotlin and learn more about competitive programming while you practice:

And if you’d like to see how the top competitive programmers approach these challenges, check out ecnerwala and SecondThread solving problems from this practice round live on stage at the ICPC World Finals in Baku.

Mark your calendars for September 12, 2025! Kotlin Heroes: Episode 13 offers 2 hours and 30 minutes of problem-solving, featuring a wide range of tasks designed for everyone, from those just starting out to experienced competitive programmers.

The use of AI-based tools during the main contest is strictly limited. To find out the guidelines for proper AI use, what is allowed and what is prohibited, please read the post "Rule Restricting the use of AI". Improper use of AI tools during the main contest may result in disqualification. Using automatic translation tools (including but not limited to neural networks and AI) to convert code written in other programming languages to Kotlin goes against the spirit of the competition, so it is also strictly prohibited.

REGISTER →

Prizes:

  • 🥇 $512 (or equivalent value) for 1st place
  • 🥈 $256 for 2nd place
  • 🥉 $128 for 3rd place
  • 👕 Kotlin Heroes T-shirts for the top 50 participants
  • 🎁 A raffle of 50 T-shirts for anyone who solves at least one problem

Please note that we are not able to ship prizes to any country, state, province, or territory subject to comprehensive OFAC sanctions, including Belarus, Cuba, Iran, North Korea, Russia, Syria, or the Crimea, Donetsk, or Luhansk regions. For complete the list, please visit this page.

Best of luck to everyone!

upd: Editorial can be found here.

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Announcement of Kotlin Heroes: Episode 13
Announcement of Kotlin Heroes: Practice 13
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By BledDest, 10 months ago, translation, In English

2112A - Race

Idea: BledDest

Tutorial
Solution (Neon)

2112B - Shrinking Array

Idea: BledDest

Tutorial
Solution (adedalic)

2112C - Coloring Game

Idea: BledDest

Tutorial
Solution (Neon)

2112D - Reachability and Tree

Idea: adedalic

Tutorial
Solution (adedalic)

2112E - Tree Colorings

Idea: BledDest

Tutorial
Solution in M sqrt M (Neon)
Solution in M log M (BledDest)

2112F - Variables and Operations

Idea: BledDest

Tutorial
Solution (BledDest)

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By BledDest, 12 months ago, translation, In English

Neapolis University Pafos

Hello Codeforces!

The series of Educational Rounds continues thanks to the support of the Neapolis University Pafos.

On Apr/28/2025 17:35 (Moscow time) Educational Codeforces Round 178 (Rated for Div. 2) will start.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Adilbek adedalic Dalabaev, Mikhail awoo Piklyaev, Maksim Neon Mescheryakov, Alex fcspartakm Frolov and me. We would like to express our gratitude to Alexey ashmelev Shmelev for testing the problems and providing us with lots of useful feedback. Also, huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

The round is partially based on the Saratov Multi-University Olympiad and the Nizhny Novgorod Regional Collegiate Olympiad, so if you participated in any of these two competitions, please skip the round.

Our friends at Neapolis University Pafos also have a message for you:

Admission to the Computer Science and Artificial Intelligence Bachelor’s program at Neapolis University Pafos is ongoing!

The JetBrains Foundation is offering 20 fully funded scholarships for talented first-year students.

Each scholarship covers the entire duration of the program, including tuition, accommodation, medical insurance, visa fees, and €300 per month for personal expenses.

Find out more about the CSAI program →

Good news! If you missed the first round, there’s still time to apply for the second round! Submit your documents, pass the entrance test and interview, and receive a full scholarship.

  • Application deadline – June 12, 2025
  • Entrance test – June 15, 2025 (this is the last entrance test for 2025!)

Additionally, there are 2 fully funded scholarships available for students wishing to transfer into the second year of the program (for those already studying Computer Science).

If you have any questions, feel free to ask in the Telegram chat or email us at nup@jetbrains.com !

upd: Unrated registration is possible now. Sorry for the inconvenience.

upd2: The editorial can be accessed here.

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By BledDest, 13 months ago, In English

The contest was prepared by adedalic, awoo, Neon and me. We had a great team of testers: shnirelman, ashmelev, FelixArg, KIRIJIJI, Alenochka, alyoks1, Vladosiya, mariibykova — huge thanks to all of you!

One insane moment from the testing phase

Thanks to all competitors for participation, I hope you enjoyed the problems we made!

And last but not least, I would like to express my gratitude to MikeMirzayanov for keeping Codeforces and Polygon running even under unprecedented pressure from the bots.

Okay, now for the editorial itself:

2087A - Password Generator

Idea: BledDest, preparation: BledDest

Tutorial
Solution (Neon)

2087B - Showmatch

Idea: BledDest, preparation: BledDest

Tutorial
Solution (Neon)

2087C - Coin Game

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2087D - Uppercase or Lowercase?

Idea: adedalic, preparation: adedalic

Tutorial
Solution (adedalic)

2087E - Color the Arrows

Idea: BledDest, preparation: awoo

Tutorial
Solution (awoo)

2087F - Weapon Upgrade

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2087G - Esports in Berland

Idea: BledDest, preparation: adedalic

Tutorial
Solution (adedalic)

2087H - Nim with Special Numbers

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

2087I - Hamiltonian Partition

Idea: BledDest, preparation: BledDest

Tutorial
Solution (BledDest)

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By BledDest, history, 13 months ago, In English

Greetings Codeforces!

First things first, we would like to thank everyone who participated in the previous eleven Kotlin Heroes competitions: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round, Episode 6, Episode 7, Episode 8, Episode 9, Episode 10 and Episode 11.

Kotlin Heroes is a great way to play around with Kotlin’s features, learn something new, and practice using the language by solving fun problems. It is great for programmers of any level!

We invite you to join the practice round, where you can improve your algorithmic problem-solving skills and complete training problems. In this round, all the solutions are open and you can request hints if you’re stuck.

Here are some things you can do to help you refresh your knowledge of Kotlin and learn more about competitive programming while you practice:

On April 7, 2025, the real challenge begins! Kotlin Heroes: Episode 12 will last 2 hours 30 minutes and will feature a range of problems – from simple tasks anyone can solve to tricky challenges for seasoned competitive programmers.

The contest will contain at least one interactive problem, so we strongly recommend that you familiarize yourself with them — for example, by solving problem F from the practice round and/or reading the Codeforces guide for interactive problems. The flush operation in Kotlin is done by calling System.out.flush().

The use of AI-based tools during the main contest is strictly limited. To find out the guidelines for proper AI use, what is allowed and what is prohibited, please read the post "Rule Restricting the use of AI". Improper use of AI tools during the main contest may result in disqualification.

REGISTER →

Prizes:

The top three winners will receive cash prizes of $512, $256, and $128 (or rewards of equivalent value), respectively. The top 50 participants will win a Kotlin Heroes T-shirt and an exclusive Kotlin sticker, and all competitors who solve at least one problem will be entered into a raffle for one of 50 Kotlin Heroes T-shirts.

Please note that we are not able to ship prizes to any country, state, province, or territory subject to comprehensive OFAC sanctions, including Belarus, Cuba, Iran, North Korea, Russia, Syria, or the Crimea, Donetsk, or Luhansk regions. For complete the list, please visit this page.

Best of luck to everyone!

UPD: You can find the editorial here. Thank you for participation!

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Announcement of Kotlin Heroes: Episode 12
Announcement of Kotlin Heroes: Practice 12
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By BledDest, 13 months ago, In English

So, if you paricipated in ER 176 and got WA2 on problem B, you might think this is a terrible problem, maybe one of the worst on CF. Let me try to explain why it was created, and maybe it will change your opinion about it (or maybe it won't).

This problem has an obvious solution: you have to maximize the sum of the first $$$k$$$ chosen elements and the last element you paint, so the sum of $$$(k+1)$$$ elements of the array. So, let's take $$$(k+1)$$$ greatest elements, add them up, and we get the answer. It even passes the sample test case, but it is wrong.

Why it is wrong

When preparing the problem, we had an option to discard the case when this greedy solution does not work. However, I didn't like that version of the problem because it just becomes a "guessforces" problem — people can just assume that you always choose $$$(k+1)$$$ maximums, submit the solution without proving it, and get Accepted. I believe we already have too many problems of this style on Codeforces.

To solve the current version of the problem, you have to actually find out what is wrong with the original idea, locate the case when the greedy solution does not work. I think that proving your solution or finding flaws in your ideas is a very important skill in programming contests, and this situation (when you have a "working" solution which does not pass the tests, and you need to find an issue with it) teaches this skill. This is also why the case when the greedy idea fails is not in the samples — otherwise finding the issue would be too effortless.

Were there any flaws with the problem itself? There was at least one, but it is not in its idea/preparation, but it is a mistake I made during the contest itself. The first global clarification for the problem was poorly worded, so some people assumed that an element has to have exactly two blue neighbours if we want to paint it. This was a mistake, and I am sorry for it. I probably should not have sent it in the first place.

But I still think that such problems should be on CF, especially because most other problems are set in a way that if you have a greedy idea which passes the samples, it passes the actual tests.

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By BledDest, history, 14 months ago, translation, In English

2069A - Was there an Array?

Idea: BledDest

Tutorial
Solution (BledDest)

2069B - Set of Strangers

Idea: adedalic

Tutorial
Solution (adedalic)

2069C - Beautiful Sequence

Idea: BledDest

Tutorial
Solution (Neon)

2069D - Palindrome Shuffle

Idea: BledDest

Tutorial
Solution (Neon)

2069E - A, B, AB and BA

Idea: adedalic

Tutorial
Solution (adedalic)

2069F - Graph Inclusion

Idea: BledDest

Tutorial
Solution (BledDest)

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By BledDest, 16 months ago, translation, In English

Neapolis University Pafos

Hello Codeforces!

The series of Educational Rounds continues thanks to the support of the Neapolis University Pafos. They offer a BSc in Computer Science and AI with JetBrains Scholarships. Gain cutting-edge skills in AI and machine learning, preparing you for high-demand tech careers. Curious? Check out the CSAI curriculum now. Limited scholarships available — don't miss your chance to study in Europe for free!

On Dec/24/2024 17:35 (Moscow time) Educational Codeforces Round 173 (Rated for Div. 2) will start.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest, you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 7 problems and 2 hours to solve them.

The problems were invented and prepared by Artem Ferume Ilikaev, Ruslan AcidWrongGod Kapralov and me. We would like to thank Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces. Also, big thanks to problem testers: Um_nik, alex.dobleaga, Stanislau, Karabutsa, Golovanov399, Timur2006, shnirelman, adedalic.

Attention: the contest uses some problems from the onsite stage of the KFU Olympiad, so if you participated in it, please refrain from taking part in the round.

Good luck to all the participants!

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By BledDest, 16 months ago, translation, In English

2051A - Preparing for the Olympiad

Idea: BledDest

Tutorial
Solution (Neon)

2051B - Journey

Idea: fcspartakm

Tutorial
Solution (BledDest)

2051C - Preparing for the Exam

Idea: BledDest

Tutorial
Solution (BledDest)

2051D - Counting Pairs

Idea: fcspartakm

Tutorial
Solution (BledDest)

2051E - Best Price

Idea: BledDest

Tutorial
Solution (Neon)

2051F - Joker

Idea: BledDest

Tutorial
Solution (Neon)

2051G - Snakes

Idea: BledDest

Tutorial
Solution (adedalic)

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By BledDest, history, 16 months ago, In English

Hello, Codeforces!

On Dec/22/2024 17:35 (Moscow time) the Codeforces Round 995 (Div. 3) will start. The round will contain 7 problems, which are mostly suited for participants with rating below 1600 (or we hope so). Although, as usual, participants with rating of 1600 and greater can register for the round unofficially. Participants with rating below 1600 can also use unrated registration to participate 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 (we hope that our tests are strong enough, so there won't be too many solutions hacked during this phase).

You will have to solve 7 problems in 2 hours and 15 minutes. The penalty for a wrong submission is equal to 10 minutes.

We remind you that only the trusted participants of the third division will be included in the official standings table. As it is written on the blog which you can access by this link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

  • take part in at least two rated rounds (and solve at least one problem in each of them),
  • not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

The problems were prepared by Neon, fcspartakm, awoo, adedalic and me. We hope you enjoy solving them!

We would also like to thank MikeMirzayanov for his Codeforces and Polygon platforms, and Vladosiya for coordinating the round.

The contest was tested by shnirelman, k1sara, leovl48, jai_hanuman_orz, saba_goduadze, JuicyGrape, RohitLakra and rahmanmehraj627. Thank you for helping us in evaluating the difficulty better and in getting rid of ambiguity in statements!

Good luck, and see you during the contest!

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By BledDest, 17 months ago, In English

2042A - Greedy Monocarp

Idea: BledDest

Tutorial
Solution (Neon)

2042B - Game with Colored Marbles

Idea: BledDest

Tutorial
Solution (BledDest)

2042C - Competitive Fishing

Idea: BledDest

Tutorial
Solution (Neon)

2042D - Recommendations

Idea: adedalic

Tutorial
Solution (adedalic)

2042E - Vertex Pairs

Idea: BledDest

Tutorial
Solution (awoo)

2042F - Two Subarrays

Idea: BledDest

Tutorial
Solution (Neon)

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By BledDest, 17 months ago, In English

Note that initially this contest was scheduled on a different day. Due to technical difficulties, we had to postpone the online mirror. We are sorry about that; if you planned to participate, but are no longer able because the contest day has changed, you can use the virtual participation option.

Hello Codeforces!

The Southern and Volga Russian Regional Contest was held in Saratov State University yesterday, on 12th of November. This contest was used to qualify the teams from Southern Russia and Volga region to the Northern Eurasia Finals.

On Nov/18/2024 13:35 (Moscow time), we will conduct the online mirror of this contest. It will last for 5 hours and is best suited for teams of three people, although it is not forbidden to participate in teams of smaller/larger size. The mirror will use ICPC rules, the same as the offline contest.

The contest was prepared by adedalic, awoo, dmitryme, elena, Neon, DmitryKlenov, MikeMirzayanov, Ferume and me. Big thanks to the contest testers: Kuroni, ashmelev, bthero, KIRIJIJI, Kniaz, vladmart, JanPlovLagman, PropeRam, pshenikita. I would like to express my gratitude to MikeMirzayanov for not only participating in the preparation process himself, but also making Polygon, which made our work much easier.

As the chief judge of the contest, I hope you enjoy the problems!

Of course, the contest will be unrated.

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By BledDest, 19 months ago, In English

This round was prepared by Neon, adedalic, awoo, shnirelman and me.

Huge thanks to all of the testers: ashmelev, KIRIJIJI, PavelKunyavskiy, soup and Fanarill! Your feedback helped us balance this contest (and find a very stupid overflow bug I'm too ashamed to mention).

Thanks for participation, we hope you enjoyed the contest!

2011A - Problem Solving

Idea: BledDest, preparation: BledDest

Tutorial
Solution (Neon)

2011B - Shuffle

Idea: BledDest, preparation: BledDest

Tutorial
Solution (Neon)

2011C - Split the Expression

Idea: BledDest, preparation: BledDest

Tutorial
Solution (Neon)

2011D - Among Wolves

Idea: BledDest, preparation: adedalic

Tutorial
Solution (adedalic)

2011E - Rock-Paper-Scissors Bot

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2011F - Good Subarray

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2011G - Removal of a Permutation

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2011H - Strange Matrix

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

2011I - Stack and Queue

Idea: shnirelman, preparation: awoo

Tutorial
Solution (awoo)
Solution 2 (awoo)

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By BledDest, 19 months ago, In English

Greetings Codeforces!

First things first, we would like to thank everyone who participated in the previous nine Kotlin Heroes competitions: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round, Episode 6, Episode 7, Episode 8, Episode 9, and Episode 10.

Kotlin Heroes is a great way to play around with Kotlin’s features, learn something new, and practice using the language by solving fun problems. It is great for programmers of any level!

We invite you to join the practice round, where you can improve your algorithmic problem-solving skills and complete training problems. In this round, all the solutions are open and you can request hints if you’re stuck.

Watch tourist and ecnerwala tackle the Kotlin Heroes practice round challenges at the ICPC World Finals in Astana.

Here are some things you can do to help you refresh your knowledge of Kotlin and learn more about competitive programming while you practice:

On September 30, 2024, the real challenge begins! Kotlin Heroes: Episode 11 will last 2 hours 30 minutes and will feature a set of problems ranging from simple ones, which are designed to be solvable by anyone, to some really tricky ones for seasoned competitive programmers.

Note that the usage of AI-based tools during the main contest is strictly limited. To find out the guidelines for proper AI use, what is allowed and what is prohibited, please read the post "Rule Restricting the use of AI". Improper use of AI tools during the main contest may result in disqualification.

Using automatic translation tools (including but not limited to neural networks and AI) to convert code written in other programming languages to Kotlin goes against the spirit of the competition, so it is also strictly prohibited.

REGISTER →

Prizes:

The top three winners will receive cash prizes of $512, $256, and $128 (or rewards of equivalent value), respectively. The top 50 participants will win a Kotlin Heroes T-shirt and an exclusive Kotlin sticker, and all competitors who solve at least one problem will be entered into a raffle for one of 50 Kotlin Heroes T-shirts.

Please note that we are not able to ship prizes to any country, state, province, or territory subject to comprehensive OFAC sanctions, including Belarus, Cuba, Iran, North Korea, Russia, Syria, or the Crimea, Donetsk, or Luhansk regions. To see the list of sanctioned countries and regions, please visit this page.

Best of luck to everyone!

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Announcement of Kotlin Heroes: Episode 11
Announcement of Kotlin Heroes: Practice 11
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By BledDest, 23 months ago, In English

We hope you enjoyed the problems! Thank you for participation.

The authors are the usual suspects: Neon, awoo, adedalic, Roms and me. Huge thanks to the testers: shnirelman, KIRIJIJI, soup, Optoed, le.mur, and the MVP tester PavelKunyavskiy. Without your insights, this round would be impossible!

1958A - 1-3-5

Idea: BledDest, preparation: BledDest

Tutorial
Solution (PavelKunyavskiy)

1958B - Clock in the Pool

Idea: adedalic, preparation: adedalic

Tutorial
Solution (PavelKunyavskiy)

1958C - Firewood

Idea: BledDest, preparation: BledDest

Tutorial
Solution (PavelKunyavskiy)

1958D - Staircase

Idea: BledDest, preparation: BledDest

Tutorial
Solution (PavelKunyavskiy)

1958E - Yet Another Permutation Constructive

Idea: BledDest, preparation: BledDest

Tutorial
Solution (PavelKunyavskiy)

1958F - Narrow Paths

Idea: BledDest, preparation: awoo

Tutorial
Solution (PavelKunyavskiy)

1958G - Observation Towers

Idea: BledDest, preparation: awoo

Tutorial
Solution (PavelKunyavskiy)

1958H - Composite Spells

Idea: Roms, preparation: Roms

Tutorial
Solution (Neon)

1958I - Equal Trees

Idea: BledDest, preparation: Neon

Tutorial
Solution (PavelKunyavskiy)

1958J - Necromancer

Idea: BledDest, preparation: Neon

Tutorial
Solution (Neon)

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By BledDest, history, 2 years ago, In English

Greetings Codeforces!

First things first, we would like to thank everyone who participated in the previous nine Kotlin Heroes competitions: Episode 1, Episode 2, Episode 3, Episode 4, Episode 5: ICPC Round, Episode 6, Episode 7, Episode 8 and Episode 9.

Kotlin Heroes is a great way to play around with Kotlin’s features, learn something new, and practice using the language by solving fun problems. It is great for programmers of any level!

We invite you to join the practice round, where you can improve your algorithmic problem-solving skills and complete training problems. In this round, all the solutions are open and you can request hints if you’re stuck.

Here are some things you can do to help you refresh your knowledge of Kotlin and learn more about competitive programming while you practice:

On May 13, 2024, the real challenge begins! Kotlin Heroes: Episode 10 will last 2 hours 30 minutes and will feature a set of problems ranging from simple ones, which are designed to be solvable by anyone, to some really tricky ones for seasoned competitive programmers.

REGISTER →

You can solve Codeforces challenges directly from your JetBrains IDE using its smart features. Just enable the JetBrains Academy plugin and follow the instructions in the Getting started with Codeforces guide.

Prizes:

The top three winners will receive cash prizes of $512, $256, and $128 (or rewards of equivalent value), respectively. The top 50 participants will win a Kotlin Heroes T-shirt and an exclusive Kotlin sticker, and all competitors who solve at least one problem will be entered into a raffle for one of 50 Kotlin Heroes T-shirts.

Please note that we are not able to ship prizes to any country, state, province, or territory subject to comprehensive OFAC sanctions, including Belarus, Cuba, Iran, North Korea, Russia, Syria, or the Crimea, Donetsk, or Luhansk regions. To see the list of sanctioned countries and regions, please visit this page.

Best of luck to everyone!

Full text and comments »

Announcement of Kotlin Heroes: Episode 10
Announcement of Kotlin Heroes: Practice 10
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By BledDest, history, 2 years ago, In English

1913A - Rating Increase

Idea: Roms, preparation: awoo

Tutorial
Solution (awoo)

1913B - Swap and Delete

Idea: BledDest, preparation: adedalic

Tutorial
Solution (adedalic)

1913C - Game with Multiset

Idea: Ferume, preparation: Ferume

Tutorial
Solution (awoo)

1913D - Array Collapse

Idea: Roms, preparation: Roms

Tutorial
Solution (Roms)

1913E - Matrix Problem

Idea: Ferume, preparation: Ferume

Tutorial
Solution (BledDest)

1913F - Palindromic Problem

Idea: Ferume, preparation: Ferume

Tutorial
Solution (awoo)

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