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.
• 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!

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

Hello, Codeforces!

We are pleased to announce the resumption of the Global Rounds. Thanks to XTX Markets for supporting the initiative! In 2024, we will hold 4 such rounds. The series results will take into account the best 3 participations out of 4.

On Oct/27/2024 17:35 (Moscow time) we will host Codeforces Global Round 27.

Codeforces Global Round 27 marks the third round in the 2024 series of Codeforces Global Rounds. These rounds are open and rated for everyone.

The prizes for this round are as follows:

• The top 30 participants will receive a t-shirt.
• 20 t-shirts will be randomly distributed among participants ranked between 31 and 500, inclusive.

The prizes for the 4-round series in 2024:

• In each round, the top-100 participants get points according to the table.
• A participant's final score will be the sum of the points they earned in their 3 highest-placing rounds.
• The top 20 participants across the series will receive sweatshirts and placement certificates.

We extend our gratitude to XTX Markets for supporting the global rounds initiative in 2024!

The 8 problems were authored by our 8 authors: Benq, lunchbox, oursaco, sum, willy108, Hori, turtletortles, and last but not least ChatGPT.

We would also like to thank:

• Our coordinatorz Sugar_fan (first time) and errorgorn (almost last time)
• Our testers jqdai0815, SSerxhs, RDDCCD, wygzgyw, fallleaves01, triple__a, tarjen, omeganot, Yam, InternetPerson10, EmeraldBlock, Cai_Guang, Tobo, jay_jayjay, Nanani, ezraft, myst-6, Mr.Pie, AbduSaber, A_Nafees, Timosh, redpanda, newb_programmer, Jasonwei08, koolkid403, ShineChang318, khluo
• Alexdat2000 for translating the statements to Russian
• the one and only KAN
• MikeMirzayanov for creating the Codeforces platform

Round Information:

• Duration: 180 minutes
• Number of problems: 8 problems with 1 subtask
• Score distribution: 250 — 500 — 1000 — 1500 — 2000 — 2250 — (2250 — 2000) — 4500

We look forward to your participation!

UPD: Congrats to the winners

1. Kevin114514
2. 275307894a
3. jiangly
4. JoesSR
5. ksun48
6. turmax
7. dXqwq
8. hos.lyric
9. Rewinding
10. jiangbowen

UPD2: First solves

A: dXqwq
B: hos.lyric
C: dorijanlendvaj
D: riantkb
E: turmax
F: taeyeon_ss
G1: taeyeon_ss
G2: Kevin114514
H: orz (only in contest solve!)

UPD3: Editorial

Hello Codeforces! Me and yud08 are excited to invite you to take part in Codeforces Round 982 (Div. 2), which starts on Oct/26/2024 17:35 (Moscow time). You will be given 5 problems and 2 hours to solve them. Two problems are divided into two subtasks.

This round will be rated for all participants whose rating is strictly below 2100.

The problems were authored by me and yud08, and prepared by me.

We would like to thank:

• abc864197532 and Vladithur for an amazing double coordination.
• Alexdat2000 for translating the statements to Russian.
• BurnedChicken for LGM testing.
• BucketPotato, Fysty, alvingogo, and WiwiHo for red testing.
• sammyuri, anango, jay_jayjay, amsraman, Intellegent, valeriu, erekle, and golions for orange testing.
• Beacon, iceylemon157, and LittlePants for purple testing.
• Jasonwei08, godgenji, Banis, temmieowo and Arthas for blue testing.
• t0rtik, lumid, and AG-88301 for cyan testing.
• vatzahellmen for green testing.
• MikeMirzayanov for the Polygon and Codeforces platforms.

We hope you enjoy the problems!

Score Distribution: $$$500 - 1000 - 1250 - (1250 + 1000) - (2000 + 1000)$$$

We actually wanted to continue the trend of posting photos of contest writers, but we could only find one photo containing both of us, which was a group photo that we took with some other UK informatics people! (I'm the one in the back of the picture who is wearing the MHC T-shirt and yud08 is the one whose head is popping out from the left side of the photo.)

UPD1: Congratulations to the winners of the contests:

Div 1:

1. jiangly
2. neal
3. SSerxhs
4. A_G
5. kotatsugame

Div 2:

1. nathan_higgs
2. purupurupururin
3. Nonoze
4. Hong_Meiling
5. Nika_Tamliani

Also, first solves! (if any of these are wrong please let me know)

• A: A_G in 00:00:45
• B: A_G in 00:03:01
• C: Alex239 in 00:05:09
• D1: 74TrAkToR in 00:09:21
• D2: 74TrAkToR in 00:18:51
• E1: jiangly in 00:38:36
• E2: jiangly in 01:01:08

UPD2: Editorial is available here

Hello Codeforces!

I am pleased to invite you all to participate in Codeforces Round 981 (Div. 3), which will start on Oct/24/2024 17:35 (Moscow time).

The format of the event will be like any Div. 3 rounds:

• 6-8 tasks;

• ICPC rules with a penalty of 10 minutes for an incorrect submission;

• 12-hour phase of open hacks after the end of the round (hacks do not give additional points)

• after the end of the open hacking phase, all solutions will be tested on the updated set of tests, and the ratings recalculated

• by default, only "trusted" participants are shown in the results table.

I encourage participants with a rating of 1600+ not to create new accounts but to participate unofficially.

Only trusted participants of the third division will be included in the official standings table. This is a forced 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),
• do 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 (or you are a newcomer/unrated), then the round will be rated for you.

Also, it will be a round with unrated register. If you already registered as rated participant you can change registration type here.

I would like to thank

• MikeMirzayanov for creating Codeforces and Polygon.

• Vladosiya for beautiful coordination and helping in preparation.

• Pa_sha, SashaT9 and Skillful_Wanderer for not only testing but also discussion of the problems.

• Hyperbolic, Irmuun.Ch for red testing.

• LMeyling, Sokol080808, Intellegent, 18o3, amoeba3, -1e11, Error_Yuan, Wandoka for yellow testing.

• wuhudsm, Viktor36, CarlosS48 for purple testing.

• adepteXiao, yellow_13, macaquedev, Pa_sha, Vinayak286, chromate00 for blue testing.

• darysani for cyan testing.

• Parag_AP for green testing.

• My friends cat Chefir who inspired one of the task statements

Good luck!

Upd: Editorial is out.