Hello, Codeforces!

I'm excited to invite you to participate in MaraTON Challenge 1, our first marathon in collaboration with the TON Foundation. It's great to see our partnership with TON thriving and moving forward.

The challenge is brought to you by TON blockchain engineers, some of whom are community members. Special thanks to SpyCheese for preparing the problem!

The competition will run for three weeks, starting on Dec/23/2024 16:35 (Moscow time). Get ready to dive deep into the technical details of the blockchain world — it's worth it.

Winners will receive amazing prizes:

• 1st place: 8,000 USDT
• 2nd place: 5,000 USDT
• 3rd place: 3,000 USDT
• 4th–10th places: 2,000 USDT each
• 11th–20th places: 1,000 USDT each

Additionally, there will be bonus prizes for the leaders throughout the competition. Starting December 25th and continuing daily until January 13th at 12:35 (UTC), we will award bonus prizes to the top five leaders of the day:

• 1st place: 250 USDT
• 2nd place: 125 USDT
• 3rd place: 75 USDT
• 4th–5th places: 50 USDT each

Please note that these prizes will be distributed after full testing of all submissions made by 12:35 (UTC) on the respective day.

Join the competition — it's truly something new and exciting on Codeforces!

* All payments will be made to a TON wallet. All payouts (including those for daily leadership) will be issued after the final results are announced.
* In case of ties in the leaderboard, the participant who first achieved the score will rank higher for prize distribution.
* Please note that this is an individual competition. Collaboration, discussing ideas, or using shared code is prohibited. Please adhere to the rules regarding the use of third-party code.

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, SashaT9, 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!

Goodbye, 2024. Hello, 2025!

Dear Santa Claus,
Please make 2025 a happy year—not just for me, but for everyone. We all need this.

Hello, 2025!

And of course, we have our traditional gifts!

Change Handle Feature

Hurry! Until the 10th of January, you can change your handle (but only once)! Note that you can roll back the changes or request another handle change only after a year. Choose wisely!

You can change your handle to a new one that hasn’t been used by anyone else, or to one that you’ve previously used. Links to your old profile will automatically redirect to your updated profile.

Again this year, if you’ve participated in at least 10 rounds, you can request the handle of an inactive participant. This means the participant must have had a period of activity on Codeforces lasting at most 180 days, and this activity must have occurred in 2020 or earlier. The inactive participant must not have posted comments, messages, or similar content, and they must not have participated in more than 2 contests. In such cases, the handle will be automatically renamed, and the original owner will be notified via email. If the original user requests their handle back, we will roll back the change and restore your previous handle.

If you’re unable to change your handle, it means some of the requirements have not been met. Please do not ask me to intervene manually. I especially dislike requests such as, "This is my second account; I took an interesting handle myself." I'm not Santa Claus!

Speaking of handles, I always reminisce about one particular story. Once, a user sent me this message: "Please change my handle from I_love_Valya to I_love_Sveta, as I no longer love Valya..."

New Year's Masquerade of Colors and Ranks

The traditional magical tab has appeared in your profile settings. Happy New Year!

Art by Evirir

Hello / Selamat sejahtera / 你好 Codeforces! ^.=.^

We, CSQ31, Evirir, and YouKn0wWho, are excited to invite you to Codeforces Round 994 (Div. 2) on 20.12.2024 17:35 (Московское время)!

In this round, you will learn more about Evirir the dragon and help (or stop) them as they wreak havoc and escape from a wizard.

You will solve $$$6$$$ problems in $$$2$$$ hours.

The score distribution is $$$500 - 750 - 1000 - 1750 - 2250 - 2750$$$.

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

We would like to thank everyone who made this round possible:

• Kaey for coordinating the round, coming up with ideas and solutions, and helping with preparation;
• Alexdat2000 for translating the problem statements to Russian;
• A_G, Alpha_Q, Darkeld, ducksaysquack, franv, JOliva, LMeyling, MASTERB4APRIL, shaili17, Tainel, and whiitex for testing our round and providing useful feedback, praises, and flames;
• You for trying out our problems; and
• MikeMirzayanov for the amazing Codeforces and Polygon platforms that support contests beyond Codeforces contests.

Fun fact: As far as we know, this is the first round by Malaysians since 2020 (last being Codeforces Global Round 10)!

UPD: The score distribution has been added.

UPD 2: Editorial

UPD 3: Congratulations to the Top 5!

Div. 2:

1. rainboy
2. natural_fruits
3. Aestivate
4. trunkty
5. 1.618034

Div. 1 + 2:

1. Rubikun
2. arvindf232
3. antontrygubO_o
4. StarSilk
5. Otomachi_Una

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 Dec/19/2024 17:35 (Moscow time) we will host Codeforces Global Round 28.

Codeforces Global Round 28 marks the fourth 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 9 problems were authored by our 4 authors: JoesSR, cmk666, wsyear and Little09.

We would also like to thank:

• Our coordinator 244mhq.
• Our friends who discussed the task with us zjy2008, Zhouershan, LXH-cat, 5ab, cyb1010.
• Our testers orzdevinwang, Um_nik, 275307894a, A_G, JCY_, A_zjzj, umbrella-leaf, wyrqwq, zltzlt, Daniel777, Error_Yuan, lgswdn, gyydp123_LIM, Daniel081024, omeganot, jimmyywang, Meatherm, operator_, Imdie, chengcheng5677, Xiaohuba, ikira.57, Hanghang007, Chenly, angryarabianman, 0x4f, Hori, OME_, huangyuheng, newb_programmer, CuteWhite, Abracadaber, Union_of_Britain, ishaandas1, dazlersan1, OIer_Chtholly.
• 244mhq for translating the statements to Russian.
• MikeMirzayanov for creating the Codeforces platform.

Round Information:

• Duration: 180 minutes.
• Number of problems: 9 problems with 1 subtask.
• Score distribution: $$$ 250 - 500 - 1000 - 1250 - 1750 - 2000 - 2250 - 2750 - (3000 + 3000) $$$.

We eagerly anticipate your participation!

UPD:

Congrats to the winners!

1. jiangly
2. turmax
3. dorijanlendvaj
4. ksun48
5. hos.lyric
6. Nachia
7. jiangbowen_
8. Ormlis
9. maroonrk
10. dXqwq

First Solves:

A: dXqwq
B: dXqwq
C: Marcin_smu
D: jiangly
E: sevlll777
F: dXqwq
G: BlackLily
H: jiangly
I1: jiangly
I2: nobody solved

UPD2: Editorial.

Hello Cowodeforces :D

Art by chromate00

vgoofficial, Lilypad and I are very to invite you to participate in Codeforces Round 993 (Div. 4), which will start on Dec/15/2024 17:35 (Moscow time). There will be $$$8$$$ problems, with one split into two subtasks, to be solved in $$$2$$$ hours and $$$15$$$ minutes. Participate or you'll have to wait another millennium for a Div. 4 round.

The format of the event will be identical to Div. 3 rounds:

• 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 (but the rating will be recalculated for all with initial ratings less than 1400 or you are an unrated participant/newcomer).

We urge participants whose rating is 1400+ not to register new accounts for the purpose of narcissism but to take part unofficially. Please do not spoil the contest for the official participants.

Only trusted participants of the fourth 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 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 point of 1400 or higher in the rating.

Regardless of whether you are a trusted participant of the fourth division or not, if your rating is less than 1400 (or you are a newcomer/unrated), you may choose to participate rated or unrated.

We want to express overwhelming gratitude to the following orzosities for making the contest possible:

• Vladosiya for reviewing the contest.

• (VIP+) chromate00 for the idea for one of the problems.

• Our testuwuers: awesomeguy856, (VIP) Dominater069, Error_Yuan, Edeeva, zrnstnsr, (VIP) LMeyling, 18o3, Intellegent, amoeba3, hbarp, efishel, ShUO-_--, larush, (VIP+) chromate00, SkibidiPilav, kevlu8, edwardmh, mathtsai, RobinFromTheHood, Filikec, macaquedev, sissi6827, and members of my high school's coding club including but not limited to IceWolf898, MatthewC3297, and ETL.

• (MVP++) MikeMirzayanov for Codeforces and Polygon.

UPD: Editorial

Hello!

On Dec/08/2024 17:35 (Moscow time) we will host Codeforces Round 992 (Div. 2).

The problems were written and prepared by Igor_Parfenov.

I would like to thank everyone who made this round possible:

• 4mda4mda, zap4eg, triple__a, Non-origination, _Israel_, ApraCadabra, FzArK, Dominater069, ezraft, thenymphsofdelphi, Pervushev, Arthas, Khomutov for testing the round and providing feedback to the problems
• Vladithur, for coordination of the round
• MikeMirzayanov, for Codeforces and Polygon platforms
• All participants

This round will be rated for participants with rating lower than 2100.

You will have 2 hours to solve 6 problems.

Score distribution: 500 — 1000 — 1500 — 2000 — 2250 — 2750.

Good luck!

UPD: Editorial

UPD: Congratulations to the Winners!

Div.2:

1. daniel6202

2. younesg

3. houseof

4. HUST_USELESS

5. FatihCihan

Div.1 + Div.2:

1. jiangly

2. maspy

3. Rubikun

4. BurnedChicken

5. neal

Hello! Codeforces Round 991 (Div. 3) will start at Dec/05/2024 17:35 (Moscow time). You will be offered 6-8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating of 1600 or higher, can register for the round unofficially.

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.

You will be given 6-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round is 10 minutes.

Remember 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)
• 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, then the round will be rated for you.

Problems have been created and written by our team: AVdovin, DanGolov, kbats183, Vladosiya and pskobx.

We would like to thank:

1. MikeMirzayanov for Polygon and Codeforces platforms.

2. Vladosiya for coordination.

3. EgorUlin, qsmcgogo, molney, misorin, vladmart, Blinov_Artemii for yellow testing.

4. snasibov05, FBI for purple testing.

5. artcosec, Pslnd, _icy_, Gabbasov, UniversalAdmin for blue testing.

6. dmit_brit, WahidmShafin, Osama.Rafat100 for cyan testing.

7. Kaushal_26 for green testing.

Good luck!

UPD: Editorial is out.

Hi Codeforces!

On Dec/03/2024 09:25 (Moscow time) we will hold Codeforces Round 990 (Div. 1) and Codeforces Round 990 (Div. 2). Note the unusual starting time!

The harder problems of this round are based on the problems from the Final round of Yandex Cup 2024, Algorithms track, that will be held at the same time.

The problems are authored by elshiko, Flyce, MrLolthe1st, sokolow, stepanov.aa, TeaTime, Tikhon228, webmonster, 4qqqq with guest problems from myst-6, Vladithur, BledDest and me.

I'd like to thank daubi, Golovanov399, arbuzick, pperm, orz, AgafonovArtem, Qwerty1232, k1r1t0, Itsmylove1, Sofi_, and errorgorn for testing the problems, tourist for helping with the round, and MikeMirzayanov for the Polygon and Codeforces systems.

Because of official Yandex Cup Finals ends later than the round on Codeforces, the upsolving, solutions, and test cases will be closed until the end of the onsite contest, roughly 3 hours after the end of the Codeforces round. It is also forbidden to discuss the problems publicly until the end of the onsite round. Any comments here concerning the problems will be removed.

Good luck!

UPD: The contest has been delayed to make sure the online contest does not start earlier than the onsite one.

Congratulations to the winners!

Div. 1:

1. jiangly
2. hank55663
3. noimi
4. cxm1024
5. Pyqe

Div. 2:

1. RGB_ICPC8
2. timer2024
3. tietieAM
4. ylzxxx7
5. mion_sonozaki

UPD: You are free to discuss the problems now.

UPD: Editorial.