Hello Codeforces!

We (pwned, ACGN, HappyPacMan, maomao90, AverageDiv1Enjoyer, and trunkty) are thrilled to invite you to Codeforces Round 987 (Div. 2) on Nov/15/2024 15:35 (Moscow time) (note the unusual time)! After more than two years of preparation and nearly thirty problems on our shortlist, our contest is finally here for your enjoyment!

In this round, you will help Penchick as he embarks on a world trip through the Philippines, Indonesia, and even through the Australian beaches and attempt six problems in two hours!

The score distribution will be as follows: $$$500-1000-1500-2000-2500-3000$$$.

This round would not be possible without the support of everyone behind this round:

• maomao90 and KAN for their excellent coordination and problem setting,
• pwned, ACGN, AverageDiv1Enjoyer, and trunkty for the creative tasks,
• HappyPacMan for his amazing technical skills in making the problems come to life,
• PiejanVDC, Shrimb, heavylightdecomp, ryuusama, and SlavicG for their unique problem ideas,
• ArvinCiu, Irmuun.Ch, bestial-42-centroids, dbscts, zscoder, NeroZein, and wfe2017 for their advice in creating interesting problems,
• _Body, ljuba, Dominater069, pavement, Rideris, Error_Yuan, NovusStellachan, Dan4Life, lunchbox, DilshodbekX, SHZhang, micho, Muhammad-Saram, culver0412, ErrorAssassin, AlperenT, iLoveIOI, newb_programmer, mwen, Erering, and LMeyling for testing our round and providing invaluable feedback, and
• You for being an awesome member of the CF community!

Lastly, we thank MikeMirzayanov for creating the incredible Codeforces platform, where many of us have engaged in friendly competition, honed our problem-solving skills, and forged lasting friendships throughout the years!

From our keyboard to yours, we (and Penchick) wish you good luck, positive delta, and an exciting competition experience!

UPD: There is at least one interactive problem, so please read the guide for interactive problems if you are unfamiliar with them.

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, H3nTa1, 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.

Hello Codeforces!

I am glad to invite you to Codeforces Round 986 (Div. 2), which will start on Nov/10/2024 18:35 (Moscow time). Note the slightly unusual start time.

The contest will run for 2 hours and have 6 tasks. The contest will only be rated for those with a rating not higher than 2099, but we welcome higher rated users to participate out of competition.

Holding the contest would have been impossible without:

• flamestorm for insanely excellent coordination, without whom this round would certainly not happen.
• Vince729 and swagchicken for lots of discussions about the problems and proposing other problem ideas :)
• conqueror_of_tourist, BucketPotato, Dominater069, sstrong, triple__a, xiaowuc1, lucasxia01, n0sk1ll, nikilrselvam, thanhchauns2, AkiLotus, bibimoni, CSQ31, mp1309, Non-origination, Qualified, redpanda, dazlersan1, fatant for testing and giving a ton of useful feedback!
• MikeMirzayanov for the wonderful Codeforces and Polygon platforms.

and of course a special thank you to all of you for participating!

Score Distribution: $$$500-1000-1500-1750-2000-2500$$$.'

UPD: The Editorial is now published.

UPD2: Congratulations to the winners!

Div 1:

1. jiangly
2. A_G
3. BurnedChicken
4. MAKMED1337
5. maspy

Div 2:

1. SUPERLWR-beta
2. mychecksdead
3. sweet_dream
4. contee
5. Sunflower233

First solves:

• A: podyapolskiy.yaroslav in 00:01:14
• B: potato167 in 00:07:38
• C: thembululquaUwU in 00:09:18
• D: jiangly in 00:17:37
• E: golions in 00:17:54
• F: MAKMED1337 in 00:10:29

Hello, Codeforces!

We (KDOI Team) are glad to invite you to take part in Refact.ai Match 1 (Codeforces Round 985), which is the 8th CP contest held by us! You can view the previous rounds by us here.

• Number of problems: $$$9$$$ ($$$0$$$ interactive);
• Start time: Nov/09/2024 17:35 (Moscow time);
• Contest duration: $$$180$$$ minutes;
• Score distribution: $$$750-1250-1750-2250-2500-3000-3500-5000-5500$$$.

The problems were authored and prepared by Error_Yuan, wyrqwq, Otomachi_Una and me sszcdjr.

A few words from our sponsor:

We’re Refact.ai, an open-source AI Coding Assistant, and on November 9th, we’ll be hosting our first round on Codeforces! Winners will receive valuable prizes, and all participants will have a chance to get some exclusive merch from us.

Refact.ai is pushing AI beyond simple code completion. Soon, we’ll launch the Autonomous AI Agent—a developer’s buddy that handles real engineering tasks end-to-end, from planning and coding to testing and deployment. You can read more about us in this announcement.

If you're excited about AI in software development and want to build the future instead of focusing on the trivial, join Refact.ai, founded by a former OpenAI researcher. We’re looking for talented Researchers and Backend developers to join our team.

Prizes:

• 1st place: 500 USDT
• 2nd place: 300 USDT
• 3rd place: 200 USDT
• 4-5th place: 100 USDT
• Top 50 participants will get T-Shirts
• Additionally, 50 random participants from the top 51-500 will receive a T-shirt

Good luck in the contest!

On the right, badges of the authors. From top to bottom, left to right are Error_Yuan, Otomachi_Una, sszcdjr and wyrqwq respectively.

We would like to thank:

• Vladithur for his wonderful coordination.
• Again, Vladithur for the Russian translation.
• programpiggy for providing a few unused problems.
• gyh20, dXqwq, Sugar_fan, 275307894a, Kubic, PEIMUDA, A_zjzj, LMydd0225, abc864197532, N_z__, rui_er, ProjectCF, chenyifanlx, MatrixGroup, wsc2008qwq, EasonLiang, cayaxi09, Hanghang007, SpadeA261, IwannaEATaCUTEcaca-qwq, OctoberEstuary, MrPython, acwing_gza, chromate00, mathtsai, Codula, tibinyte for testing and giving useful feedbacks.
• You, for participating and getting positive delta.
• Last but not least, MikeMirzayanov for great Polygon and Codeforces platforms.

Good Luck & Have Fun!

UPD1. The Editorial was published.

UPD2. Congratulations to the winners!

1. Benq
2. jiangly
3. hos.lyric
4. Radewoosh
5. arvindf232
6. Nachia
7. ksun48
8. Szoboszlai10
9. Endagorion
10. _Serge_

Hello Codeforces!

Hello Codeforces! As we wrap up another exciting round of our Kotlin Heroes series, it’s time to celebrate the champions who navigated the challenges like pros. With high stakes and impressive typing speeds, we witnessed incredible talent. Join us as we highlight the winners!

The top three contestants:

1. arvindf232
2. tourist
3. Golovanov399

A Kotlin Heroes T-shirt and exclusive Kotlin stickers will be presented to:

These participants also won branded T-shirts:

We will contact the winners soon to coordinate the delivery of their prizes!

It's great to see new people learning Kotlin and performing brilliantly in the competition. Challenges from all eleven previous rounds are available for practice here: 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.

For those who would like to get to know Kotlin better, take a look at Basic Kotlin (solve Koans), Kotlin Playground, this competitive programming tutorial, and these videos on competitive programming in Kotlin.

We wish you luck and hope you enjoy Kotlin!

Hello, Codeforces.

We're Refact.ai, an open-source AI Coding Assistant, and on November 9th, we'll be hosting our first round on Codeforces! It will be a combined Div.1+Div.2 round. Welcome!

The winners will receive valuable prizes, and all participants will have a chance to get some exclusive merch from us.

Refact.ai is pushing AI beyond simple code completion. Soon, we'll launch the Autonomous AI Agent—a developer's buddy that handles real engineering tasks end-to-end, from planning and coding to testing and deployment.

If you're excited about AI in software development and want to build the future instead of focusing on the trivial, join Refact.ai, founded by a former OpenAI researcher. We're looking for talented Researchers and Backend developers to join our team.

We already have competitive programmers on board, such as humbertoyusta and Rox. As humbertoyusta puts it, "Working at Refact.ai feels like being part of a team that's constantly pushing the boundaries of what's possible." If that sounds like your kind of environment, fill out this form for full-time positions (remote or in Barcelona).

If you're not open to new job opportunities but want to delegate tedious tasks and climb the leaderboard faster, explore: Refact.ai — an Open-source AI Coding Assistant that helps you create more while coding less.

Refact.ai already empowers you to code smarter. How?

• Built around your codebase, it provides accurate auto-completions powered by best-on-market Retrieval-Augmented Generation (RAG).
• Integrated in the IDE chat is already aware of your codebase and answers your questions right within your editor. (Compare it with Copilot and see the real power:)
• Detects and fixes bugs, writes unit tests, explains complex code, and much more!

Assign tasks in natural language, select from models like GPT-4o, GPT-4 Turbo, Claude 3.5 Sonnet, or Grow-Llama-3.1, and Refact.ai will generate the code for you.

• Get 3 months of the Pro Plan for free: Refact.ai has a special gift for the Codeforces community. Just use the promo code CODEFORCES to redeem it.

• Join the Discord community: Collaborate with like-minded developers and discuss the latest news and research.

• Contribute to Refact.ai: As an open-source project, Refact.ai welcomes your contributions—join us in building the future of programming together!

We hope you enjoy the problems and have a great time participating in the round!

Hi Codeforces!

We would like to invite you to participate in Codeforces Round 984 (Div. 3) on Nov/02/2024 17:35 (Moscow time). You will be given 7 problems and 2 hours and 15 minutes to solve them. The penalty for an incorrect submission will be 10 minutes. There may be interactive problems in the round.

The round will be ruled according to the standards of educational rounds (extended ICPC). Thus, 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 open hacks all accepted solutions will be rejudged on successful hacks. We've tried to make decent tests — just like you, we'll be upset if you have dropped solutions after the end of the contest.

Reminder that only trusted Division 3 competitors will be included in the official results table. This is a forced measure to combat unsportsmanlike behavior. To qualify as a trusted Division 3 competitor, one must:

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

Whether you are a trusted Division 3 participant or not, if your rating is less than 1600, the round for you will be rated.

The tasks were authored and prepared by a team consisting of Seny, eugenechka.boyko.2_0-0 and myself.

The round is based on the recent Lipetsk Team Programming Olympiad for school students. Please note that if you are a participant of the Olympiad, you are not allowed to participate in this round. Thanks to the coordinator of this Olympiad myav and the author Small_machine, whose tasks were not included in this round due to their high complexity.

We thank very much:

• Vladosiya for excellent coordination
• 74TrAkToR, Sokol080808, FBI, ssor96, itz_pabloo, IceHydra, justlm, SashaT9, nirjoy_139, lorenzotinfena for testing the round
• MikeMirzayanov for creating the wonderful Codeforces and Polygon platforms.
• You for participating!

We hope you find the problems interesting. Good luck!

UPD.: Editorial

Hello Codeforces!

$$$\newline$$$

It's been a while, today AkiLotus and I are delighted to invite you to participate in Codeforces Round 983 (Div. 2). This round will be rated for all participants with a rating lower than 2100.

Our round will start on Nov/01/2024 17:35 (Moscow time). You will be given 6 problems and 120 minutes to solve them.

This contest is a collaboration between AkiLotus, his friends and Code Mely, a Vietnamese community and an individual passionate about Computer Science. Reach out to us here.

Special thanks to:

• MikeMirzayanov for interesting Codeforces and Polygon platform.
• Artyom123 for coordinating the round.
• Teja-Smart, Xylenox for preparing sauce for chicken nuggets.
• Our talented authors: MofK, Kuroni, AkiLotus, thanhchauns2
• Our testers: cdkrot, unalive, neko_nyaaaaaaaaaaaaaaaaa, Ste, Pirate_King, Kude, tablemoon, blitztage, Dominater069, Hyperbolic, stefdasca,xuanquang1999, Railgun, towrist, mwen, FairyWinx, tibinyte, dorijanlendvaj, kokokuro, nor, SPyofgame.
• Our testers and preparation team from Code Mely: me, bibimoni, Yugi.Hacker, mp1309, nguyenphong233, CoolManGame, Tran_Thi_Thanh_Van, fanwen, DOCUTEE
• KFC for their chicken nuggets again.
• You for participating.

$$$\newline$$$

Score distribution: $$$500 - 750 - 1250 - 1750 - 2250 - 3000$$$

Happy coding! Our chicken nuggets and Fubao bless you.

UPD1: Editorial is published.

UPD2: Congratulations to the winners!

Div. 1 + Div. 2:

1. Nachia
2. arvindf232
3. peti1234
4. turmax
5. superguymj
6. Rubikun
7. ksun48
8. potato167
9. BurnedChicken
10. Vincella

Div. 2 (official):

1. Vincella
2. SUPERLWR-beta
3. BlackLily
4. leolin0214
5. TAIYANGFENG
6. xiaowangba
7. piasticOuO
8. Nikephoros2Phocas
9. SkyWave2024
10. zsj6315

First solves:

• A: Vincella (00:01:19)
• B: Vincella (00:05:48)
• C: intij_tk (00:04:36)
• D: penguin133 (Div.1, 00:11:27), Tonni_and_Huy (official, 00:20:33)
• E: awesomeguy856 (Div.1, 00:20:09), kaiboy (official, 00:37:08)
• F: peti1234 (Div.1, 00:19:54), rainboy (official, 00:36:03)

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? Join the livestream on Tuesday, October 29 at 5:00 pm UTC to learn about the CSAI program’s curriculum, course structure, scholarships, student internships, and their hands-on learning approach.

Want more experience in coding and math competitions?
JetBrains Youth Challenge returns in November 2024!

Who can join?
Ages 13–18
Anyone currently enrolled in secondary education
Register now

On Oct/28/2024 17:35 (Moscow time) Educational Codeforces Round 171 (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, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also, huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

UPD: Editorial is out