Hi, Codeforces!

I'm delighted to invite you to the best/second best/third best round of 2025 so far! Codeforces Round 997 (Div. 2) will be held on Jan/17/2025 17:35 (Moscow time). You will be presented with at least $$$6$$$ and at most $$$6$$$ problems, one of which might be divided into two subtasks, and $$$2$$$ hours to solve them.

Many of you may not believe it, but the problems were authored and written by nifeshe with a great help from maomao90. Moreover, I would like to thank:

• maomao90 for coordinating the round and helping with tasks ideas/preparation.

• Alexdat2000 for translating the problems to Russian.

• All of our testers: errorgorn, A_G, LipArcanjo, _istil, Markadiusz, Error_Yuan, Intellegent, mwen, LMeyling, hazzlek, iLoveIOI, Rideris, DilshodbekX, chromate00, tibinyte2006 for, believe it or not, testing.

• MikeMirzayanov for the Codeforces and Polygon platforms.

• Bliznetc for playing chess with me.

• And You for participating!

The score distribution is as follows: $$$500-1250-1500-2000-2250-(2750+1250)$$$.

I hope you will find a non-empty subset of problems to be interesting. Good luck!

UPD 1: Editorial

UPD 2: Congratulations to the top 5!

Div. 1 + 2:

1. maspy
2. BurnedChicken
3. jiangly
4. antontrygubO_o
5. Sugar_fan

Div. 2:

1. OdtreeKing
2. saaaalty
3. STUDENT0
4. rainboy
5. MamurjonDeveloper

UPD 3: First solves:

A. 00:02:01 by hitonanode

B. 00:02:17 by pipi0818

C. 00:03:52 by Proof_by_QED

D. 00:13:53 by wishgoodluck

E. 00:18:06 by zdc123456

F1. 00:27:48 by peti1234

F2. 00:28:40 by rainboy

Hellowo Codeforces o7

cry, larush, chromate00, LMeyling, Lilypad, and I are ebullient to welcome you to participate in Codeforces Round 998 (Div. 3) at Jan/19/2025 17:35 (Moscow time). We have cooked up $$$7$$$ problems to be solved in $$$2$$$ hours and $$$30$$$ minutes.

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 in an unorthodox manner, you will be banished off the face of the earth (trust me).

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 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).

We would like to orz the following individuals for making the contest possible:

• Vladosiya for coordinating our round.

• Our army of testuwuers: [VIP] awesomeguy856, [VIP] Dominater069, omeganot, Error_Yuan, Intellegent, -firefly-, amoeba4, 18o3, efishel, Edeeva, yoru_sacri, Abhishek_Srivastava, Vladosiya, macaquedev, DivinePunishment, Filikec, reirugan, pianapolataa, ETL, and Rahuldeb5,

• (MVP+++) MikeMirzayanov for developing the platform that will soon host Codeforces Round 1000.

Hello, Codeforces!

I'm pleased to invite you to open up the new year with Codeforces Round 996 (Div. 2) on Jan/12/2025 17:35 (Moscow time)! You will assist Florida Man through his whimsical adventures with $$$6$$$ tasks in the span of $$$2$$$ hours. The score distribution is as follows:

$$$\ \ \ \,$$$ $$$\ \ \ \,$$$ $$$\ \ \ \,$$$ $$$\quad\,$$$ $$$\quad\ $$$ $$$\ \ \ $$$

The problems were written and prepared by me, innocentkitten. However, this round would not have been possible without:

• maomao90 for coordinating the round and carrying me in general;

• Alexdat2000 for translating the problems to Russian;

• all of our testers: Anonymous_Noob, chromate00, Error_Yuan, HappyPacMan, Hyperbolic, ishaandas1, _istil, LMeyling, mohit458, NayemVai, priyanshu.p, raztun, sevlll777;

• MikeMirzayanov for the Codeforces and Polygon platforms;

• and You, for participating!

We hope you find that the problems are interesting, and that you earn your desired rating gains! or losses, if you somehow want that

UPD 1: The editorial is up! Hope you enjoyed the contest!

UPD 2: Congrats to the top 5!

Div. 1 + 2

1. Forested

2. maspy

3. potato167

4. A_G

5. Otomachi_Una

Div. 2

1. loK10

2. turgon314

3. BINYU

4. dialnote

5. _Enana

First clears

A. aryan12, 00:00

B. ankan.2526, 00:03 (Div. 1 + 2: arvindf232, 00:03)

C. Sunflower233, 00:11 (Div. 1 + 2: DE_aemmprty, 00:07)

D. suharius, 00:32 (Div. 1 + 2: Survivor_winner, 00:18)

E. myheartwaing, 01:50 (Div. 1 + 2: tute7627, 00:37)

F. N/A (Div. 1 + 2: maspy, 01:04)

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 13:35 (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 13:35 (UTC) on the respective day. The results are published here: https://mirror.codeforces.com/r/maraton-1-leadership-awards

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.

UPD: Here is the link to the table with the current progress on rewards for daily leaders: https://mirror.codeforces.com/r/maraton-1-leadership-awards

The Registration for the 48th Petrozavodsk Programming Camp is open.

THE CAMP WILL BE HELD ONLINE from January 28 to February 04, 2025.

For teams from the EAEU, offline participation is possible; details are in the information letter.

Teams of up to 3 members are invited to join

The level of contests: for participants of the semi-finals and finals of the ICPC World Championship

The training Camp schedule consists of 7 contests and 1 day off between them, preliminary schedule: camp.icpc.petrsu.ru/2025w/schedule

For each contest, a problem analysis will be broadcast in English.

The registration fee for participants from the EAEU countries is 10200/18600 rubles per participant (depends on meal inclusion).
The registration fee for participants from other countries is $150 per participant.

To register, the team coach should write a letter to the organizers.
After agreement, each team member must go through individual registration on the site of the Camp.

Contact Information

• Contact the organizers: camp.icpc.petrsu@gmail.com
  
• Website: camp.icpc.petrsu.ru
  
• Group in VK: vk.com/camp_acm_petrsu
  

Hi everyone!

Supported by

We are very happy to announce that Osijek camp is back this Winter, on February 15-23, 2025, right before the 2025 ICPC Europe Championship on February 28 — March 2, 2025. The camp is hosted by the School of Applied Mathematics and Computer Science of the University of Osijek and is brought to you by the organizing team of adamant and -is-this-fft-.

The camp is inspired by various competitive programming camps that we attended during our active years in ICPC, and is aimed to help college students prepare for ICPC regional contests and finals. The camp will consist of 7 ICPC-style contests and 2 days off.

Details

If you're participating in ICPC APAC, or are close to Singapore, please consider the Singapore mirror organized by errorgorn.

After some discussions with participants, and also thanks to the continued support of our sponsors, we decided to reform the structure of participation fees for the camp. While previously, participation fees were 100€ and 150€ per participant for online and onsite participation correspondingly, in this camp the participation fee for both online and onsite participants is 201€ per team.

For a full 3-person team, this marks a 33% reduction in the price of online participation, and a 55% reduction in the price of onsite participation! We hope that it will help us to incentivize onsite participation, and also participation in full teams, to make sure that it is as close as possible to the intended ICPC contest experience for everyone involved.

Note that, similar to previous camp editions, the fee does not include regular meals, travel or accommodation. Some further details about location, travel and food options can be found on the website.

We support and empathize with those affected by the ongoing war in Ukraine, therefore we offer a free participation for affected individuals and teams affiliated with Ukrainian institutions.

The expected starting time for the contests is 10am CET. For online participants, it is still a preferred starting time, but we will make accommodations for virtual participation at a later time, when necessary.

Most of our contests are originally developed for the camp. A small number of contests may be based on previous contests that have not been released to the general public. If you have seen some problems of a contest before, you can't participate on that day. We will privately contact participants who might be affected.

After the camp, we will have a silence period during which camp materials will not be released to the public. We ask participants not to discuss the problems in public unless they obtained an explicit permission from contest authors.

If you would like to get a feel of the contests, you can find links to some of the previously published camp contests here.

Participants

If you are interested in participating, please fill the form here.

We ask you to register before February 8 if you want to participate online and before February 1 if you want to participate onsite. If you require a visa, please register as soon as possible, as it might take a few weeks to receive (depending on location).

Also, if your university or organization has a lively ICPC community that may be interested in attending the camp, and you have some contacts of people in charge (e.g. coaches) we would highly appreciate if you could share some details in a direct message to me. Thanks!

Problemsetters

We'd like to thank and praise the authors of the contests in the camp:

• Yarema, PetroTarnavskyi, mshcherba — a team from Ivan Franko National University of Lviv, who participated in the 47-th (Luxor, Egypt) and the 48-th (Astana, Kazakhstan) ICPC World Finals.
• ntherner — Codeforces (ex?)grandmaster, IOI 2024 gold medalist, author of under 15 competitive programming problems.
• tibinyte2006 — Codeforces newbie, ex-Codeforces pupil, author of over 15 competitive programming problems.
• AmirrzwM — ICPC 2024 World Finalist, Author of Codeforces Global Round 23 and Rayan Selection Round, Iranian National Olympiad in Informatics (INOI) Silver Medalist.
• MohammadParsaElahimanesh — Main Author of Codeforces Global Round 23 and Rayan Selection Round, INOI Silver Medalist. Best problem solver on Quera.
• Halzion — ICPC 2023 world finalist.
• Claris — ICPC 2017 and 2018 world finalist. Top contributor of QOJ.
• ToniB — IOI 2023 bronze medal and CERC 2024 first place.
• ppavic — triple IOI gold medalist.
• dorijanlendvaj — double IOI gold medalist, Codeforces Legendary Grandmaster.
• Pyqe — IOI gold medalist, author of IOI 2024 Nile and Tree.
• Kinon — IMO bronze, silver, and gold medalist.

... And others. We would also like to thank errorgorn and Um_nik for their help with reviewing problem proposals. You can find more details about contest rules and technical setup on the website.

Special thanks

Finally, we say special thanks to

• our sponsors, who make the camp possible;
• ICPC foundation for their help and support;
• Codeforces for guidance and promoting this announcement to the main page;
• eolymp for providing an online judge for the contests;
• School of Applied Mathematics and Computer Science of the University of Osijek for the invaluable help and providing a physical location for the camp.

Hello to all fans of competitive programming and Codeforces enjoyers! We're happy to invite you to participate in Hello 2025, which will take place on Jan/04/2025 17:35 (Moscow time).

We, I_love_kirill22, dope, and induk_v_tsiane, have prepared 8 problems for you, and you’ll have 2 hours and 30 minutes to solve them. One of the problems is divided into 2 subtasks. The round will be rated for all participants.

Huge thanks to MikeMirzayanov, geranazavr555, and KAN for great systems Polygon and Codeforces!

Special thanks also go to:

• FairyWinx for coordinating this round, finding testers, and providing moral and technical support.
• turmax, LeoPro, Kapt, sevlll777, Pechalka, Adam_GS, evjeny_23, Iura_Shch, Noobish_Monk, Chalishkan, BottleOfJuice, v0s7er, Error_Yuan, zwezdinv, RP-1, mz1, RomkaRS, epcgmein, golikovnik, and KiruxaLight for testing.
• Anna Zaitseva for the moral support of all our projects.

Score distribution: 500 — 1000 — 1500 — 2250 — (1000+2000) — 3500 — 3750 — 4500

UPD (Update!) (Update! Yey!) Editorial — link

This round was prepared with the support of T-Generation. If you are a Russian-speaking student, please switch to the Russian version of this blog. There you will find information about our educational projects that may be interesting for you.

UPDATE

Congratulations to the winners:

1. jiangly

2. ksun48

3. ugly2333

4. Flamire

5. Ormlis

6. hos.lyric

7. ecnerwala

8. noimi

9. maspy

10. arvindf232

Hello, Codeforces!

Only a couple of days remain until 2025. To wrap up the year, I'm bringing an update — I hope you'll find it useful.

Now, you can automatically find and add random problems for your mashup based on a range of criteria and restrictions. The problems are sourced from the archive, and unusual problems are automatically excluded.

So, click the "Add random problems" link under the problem list and proceed to the addition form.

Here's what you can do:

• Exclude problems that registered mashup participants have solved/attempted/authored (a problem will be excluded if at least one registered participant is familiar with it),
• If the mashup belongs to a group (e.g., your training group), exclude all problems from other contests in that group,
• Exclude problems with subtasks — such problems are often interconnected or reference each other,
• Simply specify a list of handles or user lists for whom familiar problems should be excluded,
• And finally, the most advanced option: in the "Problem Requirements" field, you can specify requirements for the problems to be added in a special format.

The "Problem Requirements" field describes the number and properties of the problems you want to find. By clicking the question mark icon, you'll see the following explanatory text.

Enter one or more lines. Each line specifies requirements for a single problem. A line must start with the Latin letter p, followed by a space, and then additional parameters can be specified:

• Short problem name (its letter in the contest);
• Problem difficulty requirements (e.g., ratings:1000-1200, ratings:2000, ratings:3000-, or ratings:-1000: leaving the number on the left or right of the hyphen empty means the corresponding boundary is not set);
• Tags (use tags: and provide a comma-separated list of tags, e.g., tags:dp, binary search, brute force): a problem containing at least one tag from the list will be selected.

Examples of requirement lines:

• "p": any problem, the letter in the contest will be assigned automatically;
• "p F": any problem assigned the letter F;
• "p ratings:2000-2400": a problem with a difficulty level between 2000 and 2400, with the contest letter assigned automatically;
• "p D ratings:-1200 tags:greedy,dp": a problem with a difficulty level of no more than 1200, containing the tag dp or greedy (or both), assigned the letter D.

When you click the "Find Problems" button, you'll be presented with a list of problems to add. You can press the button repeatedly to generate different lists. In this list, you can mark the problems you like and finally add them to your mashup.

Note that next to the "Find Problems" button, after pressing it, additional statistics will be displayed. These can help you navigate the ratings of available problems under the specified restrictions.

I hope this makes finding problems for your training sessions and competitions easier.

Good... yes, good afternoon, Codeforces!

We are glad to invite you to take part in Good Bye 2024: 2025 is NEAR, which will start on Dec/28/2024 17:35 (Moscow time). You will be given 9 problems and 3 hours to solve them. One of the problems will be divided into two subtasks.

All the problems are authored by _istil and me.

In this round, we would like to say goodbye to the past bad memories. However, the point is we won't say goodbye to:

• TheScrasse for his cherrish coordination as always.
• Alexdat2000 for Russian Translation.
• dqstz for providing a problem proposal that was not used.
• LMydd0225, Error_Yuan, and N_z__ for helping with preparation on Polygon (including testing).
• Tony2_CF for improving a task, and KAN for improving the statement of many tasks.
• StarSilk, and jqdai0815 for LGM testing.
• nullptr_qwq, cat_of_Nesraychan, and Gabp for red testing.
• Caylex, tzl_Dedicatus545, juan_123, erray, jer033, Imdie, ABitVeryScaredOfWomen, MythicFish, anango, and min_inf for orange testing.
• IwannaEATaCUTEcaca-qwq, _TernaryTree_, doujinshi_master, PaciukZvichainyi, Dulustan, Eclipsar, and FFTotoro for purple testing.
• Chancylaser, jonatas57, SopaconK, jager59, and Fesdrer for blue testing.
• SkyWave2022, and mikcf for cyan testing.
• ishaandas1 for green testing.
• (_nikd_, Damdam307, OgradL), and (acoatoitgs, LaMatematica14, Alenygam) for team testing.
• sszcdjr for being invited to test but refuse to check a single problem at an excuse of Chemistry papers; and 251Sec for being invited to test but have no time to do virtual.
• MikeMirzayanov for the great Codeforces and Polygon platform.

UPD: The score distribution is $$$500 - 1000 - 1250 - 1750 - 2000 - 2500 - 4250 - 4500 - (3000 + 2000)$$$.

UPD: as pointed out here, the official solution of 2053I2 - Affectionate Arrays (Hard Version) is wrong. We are not sure that the problem is solvable with the current constraints. We will decide how to deal with this issue within tomorrow.

UPD: the problem I2 was removed from the official contest. Its statement has been corrected for future use. The affected participants have been unrated from the contest.

UPD: Congratulations to the winners!

1. jiangly
2. ecnerwala
3. Benq
4. Egor
5. Radewoosh
6. Petr
7. Ormlis
8. ksun48
9. Nachia
10. EnofTaiPeople

We are pleased to announce that NEAR has supported the round!

The featured prizes in NEAR are:

• Ⓝ 512 for the first place,
• Ⓝ 256 each for places 2 and 3,
• Ⓝ 128 each for places 4 to 7,
• ...
• Ⓝ 1 each for places 512-1023 places.