cry and I are very very very excited to invite you to participate in Codeforces Round 1020 (Div. 3), which will take place on Apr/24/2025 17:35 (Moscow time). You will be given 7 problems and 2 hours & 15 minutes to solve them. There will be at least one interactive problem, so please make sure to read this guide if you are not familiar with the format. One of the problems will be split into two subtasks.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of open hacks. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of 10 minutes for each wrong submission, following the rules of educational rounds.

Remind yourself that only the trusted participants of the third division will be included in the official standings table. As it is written by 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 five rated rounds (and solve at least one problem in each of them)
• not have a rating of 1900 or higher at any moment in time.

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 (unless you register unrated).

Also, note the rule restricting the use of AI. If you are caught while breaking this rule, you will be terminated and haunted. So for your own safety, please do adhere to this rule.

This round would really not be possible without the help of the following people:

• cry for coordinating the round and being kind enough to offer a problem for the set and Vladosiya for statement translation;
• cowthecow and rangerscowboys for their initial contribution to the problemset with unused and impossible problems;
• the non finite amount of testers: Dominater069, Intellegent, -firefly-, Proof_by_QED, __baozii__, Edeeva, Timosh, Friedrich, reirugan, yoru_sacri, IceWolf898, rangerscowboys, rewhile, chromate00, RE_Prince, Furyna, Banis, pop, beaten_by_ai, pianapolataa, Ashrayy, cowthecow, macaquedev, larush, ETL, bricked_, sbreger60, Lapca5, and other people from cry's basement;
• MikeMirzayanov for the amazing Polygon & Codeforces platforms;
• You for participating.

I hope to see you in the contest, and that you will be an honest and fair participant.

UPD: Editorial

UPD2: Winners!

All participants:

1. Hamed_Ghaffari

2. maspy

3. TKT_YI

4. BurnedChicken

5. DevastatingStrike

Trusted & Rated participants:

1. iren_eustia

2. tarunnnnn

3. alyzha

4. nan1669

5. CR7MEN7ALI7Y

Hello, Codeforces!

NemanjaSo2005 and I are glad to invite you to Codeforces Round 1019 (Div. 2), which will start on Apr/21/2025 17:35 (Moscow time). You will be given 6 problems and 2 hours to solve them.

The round will be rated for participants of Division 2 with a rating lower than 2100. Division 1 participants can participate unofficially.

All problems are invented and prepared by NemanjaSo2005 and me.

We would like to thank:

• MikeMirzayanov for the Codeforces and Polygon platforms!

• maomao90 for his great coordination of the round!

• Alexdat2000 for helping translate the round!

• prvocislo for being the MVT (Most Valuable Tester)!

• A_G for nutella testing!

• milisav, N_z__, _istil, TimDee, culver0412 and Error_Yuan for red testing!

• Pekiban and FEDIKUS for orange testing!

• Phantom_Performer, RTE and Friedrich for purple testing!

• beaten_by_ai, larush, Acanikolic73 and AlphaMale06 for blue testing!

• You for participating!

The score distribution is $$$500 - 1000 - 1500 - 2000 - 2750 - 3000$$$.

We hope that you will participate and enjoy the round!

UPD: We are aware of people cheating on problem F. We are looking into it and are going to make sure to ban as many of them as we can!

UPD 2: Editorial

UPD 3: Congratulations to the winners!

All participants:

1. maspy

2. Nachia

3. kotatsugame

4. abc864197532

5. Little_Sheep_Yawn

Rated only:

1. HS90R

2. oreg0na1

3. bssss_a

4. _.Ali._

5. miumah

✨ It took over a year, but it's finally here! ✨

Hello everyone! :D

We are proud to invite you to participate in Neowise Labs Contest 1 (Codeforces Round 1018, Div. 1 + Div. 2), which will be held on Apr/19/2025 17:35 (Moscow time).

The round will be rated for everyone. You will be given 8 problems and 2 hours to solve them. One of the problems will be interactive, so make sure to read the guide for interactive problems before the contest.

All problems were authored by thenymphsofdelphi and me.

We would like to thank the following people:

• 244mhq, for coordinating the round;
• 7oSkaaa, ItsNotMeItsYou, Error_Yuan, Hori, larush, N_z__, omeganot, RobeZH, Um_nik, user202729, VHPro, zltzlt, for testing;
• MikeMirzayanov, for creating Codeforces and Polygon;
• Last but not least, you, for participating!

Scoring distribution:

See you soon, and we hope you find the contest ✨ wonderful! ✨

And now, a word from our sponsor!

Neowise Labs is a proprietary trading firm founded by dark_ai, Igor_Kudryashov and Edvard. Most team members in Neowise Labs have maths and programming olympiad backgrounds. You can read more about us in the recent Codeforces post.

We’re open to find and work with new team members from the Codeforces community. If you’re interested in research, infra or other positions please fill out the form.

We’ve prepared presents for the winners and participants of the round:

• The best three participants will receive Apple Macbook Air M4 13'.
• The top 50 and random 50 participants from the top 500 will receive Neowise Labs caps.
• We also prepared valuable presents for some of the top 500 contestants but the formula to choose those contestants is a secret and will be revealed after the contest is finished, sha512 checksum for the formula is below: 7b55c594304f082436ee82bc051cf209254c103ef4545a4045c61e5d8340426a8124d8e5b5f1e1da8e534e72c4336255bd0443e5a47e35c03c6dd55ae5cbc1cc

Best of luck on the contest and have fun!

Update 1: The scoring distribution has been announced!

Update 2: Seems like a notorious coincidence.

Update 3: The editorial has been released.

Congratulations to our winners!

1. maroonrk
2. BurnedChicken
3. ksun48
4. hos.lyric
5. tourist
6. heuristica
7. Benq
8. Radewoosh
9. zhoukangyang
10. maspy

(I'm too lazy to write a post so I copied last year's, thanks feeder1 and pooty)

Hello, Codeforces community!

We are happy to invite you to participate in National University of Singapore (NUS) CS3233 Final Team Contest 2025 Mirror on Apr/14/2025 12:15 (Moscow time). CS3233 is a course offered by NUS to prepare students in competitive problem solving.

The contest is unofficial and will be held in Codeforces Gym. Standard ICPC rules (Unrated, ICPC Rules, Teams Preferred) apply. The contest is unrated. Note the unusual starting time.

The problems are written and prepared by user202729, rama_pang, feeder1, lovemathboy, tzaph_ and huajun.

We would also like to thank:

• Prof. Steven Halim for coordinating and teaching the CS3233 course;
• benson1029 as teaching assistant;
• yuto1115, Pyqe, Kinon, ArvinCiu, limanjun, caan_do, thanatos, mycho for testing the contest;
• errorgorn for existing;
• the Kattis team for the platform used in the CS3233 course and in the official contest;
• Codeforces Headquarters for letting us announce on the main page; and finally
• MikeMirzayanov for the amazing Codeforces and Polygon platform!

The contest will last for 5 hours and consist of 13 problems. While it is preferred to participate in a team, individual participation is also allowed.

The problems themselves may be quite standard as they are targeted toward those who have just learned competitive problem solving. However, we have also included a few challenging problems for stronger teams, such as ex-IOI or ICPC participants taking part in the course as well. So, the participants can expect a good mix of problems of varying difficulty levels, that we hope can be educational!

We hope you will enjoy and have fun in the contest. Good luck!

UPD: Thank you for your participation, sorry for the issues with the long queue. Editorial has been uploaded here

Good Morning/Afternoon/Evening/Night Codeforces

This is Orangutini Ananasini Emoji

cry and I are overjoyed to welcome you to participate in Codeforces Round 1017 (Div. 4) at Apr/13/2025 18:35 (Moscow time). Note the unusual time of the round. You will be given $$$2$$$ hours and $$$15$$$ minutes to solve $$$8$$$ problems.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks. After open hacks all accepted solutions will be rejudged on successful hacks.

Note that the penalty for each wrong submission in this round is 10 minutes. Also, note the rule restricting AI use!!! If you are caught using AI, your submissions will be skipped, then your account will be banned, and I will possibly even publicly shame you.

Remember that only the trusted participants of the fourth division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the fourth division, you must:

• take part in at least five rated rounds (and solve at least one problem in each of them)
• do not have a rating of 1400 or higher.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400, then the round will be rated for you (unless you register unrated).

We would like to thank the following people for making the contest possible:

• Vladosiya for coordinating and Russian translations.

• Our army of testuwuers: [VIP] Dominater069, Error_Yuan, Edeeva, -firefly-, efishel, Intellegent, temporary1, amoeba4, 18o3, [VIP] satyam343, __baozii__, rewhile, reirugan, yoru_sacri, [VIP] Friedrich, SpyrosAliv, [VIP+]chromate00, beaten_by_ai, mathtsai, pianapolataa, [VIP-] macaquedev, Filikec, pop, kevlu8, AG-88301, and members of cry's school club.

• (MVP+++) MikeMirzayanov for Codeforces and Polygon as usual

EDIT: There used to be a meme picture on this announcement. Unfortunately I was not aware of its potential political implications. It has since been removed.

EDIT 2: As a replacement to the controversial image, we have brought Orangutini Ananasini Emoji. Say hi to Orangutini Ananasini Emoji. Hi Orangutini Ananasini Emoji!

EDIT 3: editorial https://codeforces.me/blog/entry/141796

The Midnight Code Cup qualification round has ended. Thanks to all participants for giving it your best!

Final rankings are here: https://ranker.codeforces.com/ranklist/602915

Problem statements and materials are available here.

As we only accepted outputs for scoring, we’d love to learn about your solution approaches – please share in the comments!

This round would not have been possible without:

• MikeMirzayanov and the Codeforces team — thanks for your support and the new scoreboard system!
• Problem setters for this round: Aksenov239, Gassa, qwerty787788, cdkrot, MaxBuzz, pvs, Solenoid555
• Testers and support: winger, isaf27, PavelKunyavskiy, naagi, tourist, NALP, timav, Taube, noxwell, nsychev
• Our amazing sponsors: Recraft.AI, JetBrains, Neon, Pinely and our newest sponsors — Jane Street and Amazon!
• Our org comittee: Sofia Tekhazheva, Karina Tinicheva and Lidia Perovskaya

Thank you all!

The Qualification round has started! Cheer for your favourite team: https://ranker.codeforces.com/ranklist/602915

We’re excited to launch the first-ever Midnight Code Cup (MCC) — a team competition featuring an online Qualification round and a 24-hour onsite Final. Expect algorithmic challenges, optimization puzzles, cutting-edge computer science, and some just plain weird problems. It’ll be exhausting. And fun.

Who are we?

A team of problem solving geeks veterans enthusiasts, eager for the return of this contest format. The idea of Midnight Code Cup was born at Recraft.AI (AI image generation and graphic design pioneers) with huge support from JetBrains (creator of Kotlin, intelligent IDEs, and AI-driven developer tools) as well as Neon (developer-first open-source database) and Pinely (HFT company powered by competitive programmers).The sponsor list is not final and will be updated.

We are also thankful to have Codeforces as our hosting partner.

Who can participate?

Teams of 3 ready to rock and roll! No programming language, affiliation or problem solving methods restrictions. You only need to be at least 18 years old and have a slightly concerning enthusiasm for coding challenges.

Save the Date

April 12, 2025: Online Qualification (4 hours) – here at Codeforces, starts at 13:00 UTC

June 7–8, 2025: Onsite Final (24 hours) – Belgrade, Serbia

Problem setters and jury: Aksenov239, isaf27, NALP, Taube, Gassa, cdkrot, PavelKunyavskiy, tourist, qwerty787788, MaxBuzz, pvs, Solenoid555, nsychev, naagi

Registration opens soon – you have enough time to find a team. Leave your email here and you will be the first to register.

See you at Midnight!

Update: We've set the start time for the qualification round (13:00 UTC). The duration has been changed to 4 hours to accommodate participants across multiple time zones, although covering all regions globally remains a challenge.

Update 2: The registration is open now: https://midnightcodecup.com

Update 3: The registration will close on April, 9th

Update 4: The Qualification round has started! Cheer for your favourite team: https://ranker.codeforces.com/ranklist/602915

Hello, Codeforces!

I’m excited to introduce to you Neowise Labs. We’re going to host an upcoming Neowise Labs Contest 1 (Codeforces Round 1018, Div. 1 + Div. 2) and have prepared presents for you. Neowise Labs was founded by Max (dark_ai), Igor (Igor_Kudryashov) and me, and here is our story.

Igor_Kudryashov and I have been in the same ACM ICPC team for many years while studying at the Saratov State University. dark_ai was in the Saint Petersburg State University team so we were competitors back then :) Those years in the university we were doing the same as all other competitive programmers: solve problems, make contests, practice, practice and practice again (and sometimes study). I’ve even enjoyed being a Codeforces platform developer in my final year of study.

Hello, Codeforces!

The TG channel team @KogutIvanTutoring is pleased to invite you to participate in Codeforces Round 1016 (Div. 3) on Apr/08/2025 17:35 (Moscow time) — another Codeforces round for the third division. This round will feature 7 problems selected in difficulty to create an interesting competition for participants with ratings up to 1600. However, anyone with a rating of 1600 or higher can register for the round out of competition.

The round will follow the rules of educational rounds. Thus, during the round, the problems will be tested on preliminary tests, and after the round, there will be a 12-hour phase of open hacking. After this phase, all successful attempts will be retested on successful hacks. We have tried to create decent tests — just like you, we will be disappointed if many solutions fail after the contest ends.

You will be offered 7 problems and 2 hours 15 minutes to solve them.

The penalty for an incorrect attempt in this round will be 10 minutes.

We remind you that only reliable participants of the third division will be included in the official results table. As stated in the link — this is a necessary measure to combat unsportsmanlike behavior. To qualify as a reliable participant of the third division, you must:

• participate in at least five rated rounds (and solve at least one problem in each of them)
• not have a rating point of 1900 or higher.

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

The problems were conceived and prepared by part of our team: fstilus, EzikBro, _icy_, Boodoochai, pskobx, gravitsapa

Also, a big thank you to:

• MikeMirzayanov for the Polygon and Codeforces systems.

• Vladosiya for coordinating the round.

• Madball, Merkurev for red testing of the round.

• a.stepanov281005, reshke, Pagode_Paiva, AC_sahER for orange testing of the round.

• Alexbrii for purple testing of the round.

• Friendiks, Wileyne, margothequeen, Tainel, darysani, Pistol_Engineer, CarlosS48 for blue testing of the round.

• im_sad_now, veliak, harpreet1237 for cyan testing of the round.

• NeNichiy, alice19, Telyatnikov_Mikhail for green testing of the round.

Good luck to everyone!

UPD. Editorial is out!

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:

• Review our Kotlin solutions for the Advent of Code algorithmic puzzles.
• Read our competitive programming tutorial.
• Watch the videos from our Kotlin in Competitive Programming YouTube playlist.
• Look at the problems from the previous practice rounds.

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.

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!