Hello Codeforces.

We are introducing a new type of problem which may appear in future Codeforces rounds, called Communication problems!

In these problems, your program would be ran twice, with different input and output formats between the runs. All variables stored in the memory will be lost between runs. However, the information given to you on the first run may be important to you for completing the second run correctly. Therefore, one of the key challenges in these types of problems would be to find a way to use the limited amount of output you are given in the first run to communicate information to the second run. Below shows a flowchart.

Flowchart for communication problems

In these problems, time and memory limits for both runs would be kept separately. For example, if a problem has a time limit of $$$2$$$ seconds, you will only get the Time Limit Exceeded if program runs for more than $$$2$$$ seconds on one of the runs, but not if both runs takes $$$1.5$$$ seconds.

It is also possible that a problem is both interactive and run-twice. There may be interaction on either run of your program. For these types of problems, it is especially important to read the problem statement carefully to ensure you are getting the input and interaction format correctly, especially regarding whether you must flush your outputs.

To give participants a feel of these new types of problems, we will hold Testing Round 20 (Unrated, Communication Problems), which will start on Nov/03/2025 17:35 (Moscow time). You will be given $$$1$$$ hour to solve $$$3$$$ run-twice problems. The problems are authored by cry, yse, SpyrosAliv, and chromate00. One problem on the set will be interactive, so you are recommended to read the guide for interactive problems if you are unfamiliar with these types of problems. Of course, this round will be unrated. Good luck, and I hope you will have fun with the new type of problem!

Edit: The contest will be in ICPC format with no pretests and hacks disabled.

Hey, Codeforces!** (*^‿^*)

Pinely is here! We are glad to invite you to participate in Pinely Round 5 (Div. 1 + Div. 2) which will start on which will start on Oct/30/2025 19:35 (Moscow time) Note the unusual time of the round.

• You will be given 8 problems and 3 hours to solve them. The round will be rated for everyone.

The problems were authored and prepared by pinely Endagorion ch_egor aleex AndreySergunin budalnik cdkrot gepardo gleb.shnshn Ormlis VArtem along with AmShZ and our special friend Golovanov399

Thanks for all your ideas, remarks, improvements and attention for details (*ˊᗜˋ*)/ᵗᑋᵃᐢᵏ ᵞᵒᵘ*

We would like to express our special thanks:

• Endagorion for curating the round on Pinely side and surviving through all storms

• errorgorn and KAN for the excellent coordination

• Testers team: Broder, jason_sun, efishel, A_G, CatsAreCool, reirugan, yuanruiqi, Wayne_Yan, madlogic, isaf27, weirdflexbutok, SirTechnical! (ﾉ◕ヮ◕)ﾉ*:･ﾟ✧

• MikeMirzayanov for the great Codeforces and Polygon platform.

And, of course, you for participating (ᵔ◡ᵔ)

Prizes: The top 15 contestants will receive branded Pinely zip hoodies. Each hoodie can be personalized with custom name patches, making every prize truly unique.

To learn more about pinely you can visit our site or you can find our colleagues on CF in pinely organization.

UPD: Score Distribution

500 — 1000 — 1750 — 2250 — 3000 — 3250 — 3750 — 5000

☆ﾐ(o*･ω･)ﾉ Editorial is HERE

Congrats to winners! And everyone for participating ♥♥♥

• tourist
• Kevin114514
• Um_nik
• Petr
• jiangly
• Nachia
• ksun48
• hos.lyric
• BurnedChicken
• potato167
• VivaciousAubergine
• yosupo
• conqueror_of_tourist
• 353cerega
• 244mhq

Assalamu alaykum, Codeforces!

We are extremely excited to invite you to first-ever-Uzbek contest Codeforces Round 1062 (Div. 4), which starts on Oct/28/2025 17:35 (Moscow time). You will be given $$$7$$$ problems and $$$2$$$ hours and $$$15$$$ minutes to solve them. We hope you will find the problems interesting.

The problems were authored by khba, Muhammadali__, JahonaliX, Nasa and Isamatdin.

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 behaviour. 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), then the round will be rated for you.

We would like to exceptionally thank:

• Vladosiya and soullless for wonderful and epic coordination.
• Kevin114514 for red-black testing.
• physics0523 for red testing.
• Friedrich, reirugan, Saturnalorbit, [VIP+] djm03178, [VIP] Intellegent, Odminbey, Arpa, catgirl, [VIP] Timosh and [VIP] cry for orange testing.
• [VIP] chromate00, khos, thismagic and M1LLI0N_PP for blue testing.
• MikeMirzayanov and KAN for the great platforms.
• and last but not least, You for participating!

Good luck to everyone and enjoy the problems!

UPD: Editorial is out

On the special day of 1024, I am very glad to invite you to participate in Codeforces Round 1061 (Div. 2), starting at Oct/24/2025 17:35 (Moscow time)

There will be six problems for you to solve in two hours, one of which will have two parts. At least one problem will be interactive, so please make sure to read the guide for interactive problem before the contest. This round will be rated for all participants with rating below 2100.

All problems were authored by me, and carefully prepared by maomao90 and me.

I would like to thank the following list of very strong individuals for making this round possible:

• maomao90 for his wonderful coordination and careful adjustments to some problems!
• MathModel for his excellent work on the editorial.
• Alexdat2000 for translating the statements into russian.
• Dominater069 and A_G for VIP testing
• Aging1986, __baozii__, PinkieRabbit, _istil, fishcathu, AC-Automation and Andreasyan for red testing.
• Darko1, K-423, -firefly-, mzen, newhar, Ye_Che, Leonard7 and wuhudsm for orange testing.
• DarkTemplarDrop, TosakaUCW, Siyah and huikang for purple testing.
• eleven-mile, the_only_noob, chromate00, MathModel, kreeeesh_17, Gingoo, cy171, arpit_kr, Leopold_Fitz for blue testing.
• jushuai_lfx and Route101 for cyan testing.
• 3alam, Aritro_, Gorko, _Robi, nlogn130, greenofyu for green testing.
• ItsAmirAli and M_902 for grey testing.
• MikeMirzayanov and KAN for the wonderful platform I have been with for 5 years.
• You, for participating.

Score distribution: $$$500 - 750 - 1500 - 2000 - 2750 - (3250 + 3250)$$$

Hope everyone will enjoy the round!

Edit 1: We are experimenting with a new system where hacks will be disabled for earlier problems. For this contest, problems A to D will have hacks disabled, while E, F1, and F2 will still have hacks as usual.

Edit 2: Editorial is posted.

Edit 3: Congratulations to the winners

Div1:

• ksun48

• TKT_YI

• peti1234

• maspy

• Sugar_fan

• potato167

Div2:

• DiegoGarcia

• donttalk

• 1225Xia

• RaresPoinaru

• zhoujingchen

• RaduM

I am very excited to invite you to participate in Codeforces Round 1060 (Div. 2), starting at Oct/19/2025 17:35 (Moscow time).

There will be 6 wowee problems for you to solve in 2 hours, some problems will have multiple parts. All problems were authored and prepared by me. This round will be rated for all participants with rating below 2100.

I would like to thank the following list of very strong individuals for making this round possible:

• satyam343 for epic coordination.
• Um_nik for preliminary review.
• The army of testers: Dominater069, sammyuri, __baozii__, Andreasyan, p0tato, _istil, nifeshe, anango, cry, wuhudsm, FetFot, [VIP] reirugan, turska, catgirl, https, That_Salamander, temporary1, -firefly-, [VIP] Proof_by_QED, [VIP+] Friedrich, efishel, Jasonwei08, Hori, Edeeva, welleyth, milind0110, kevlu8, Non-origination, lucaski2, vladimirfilip, dazlersan1, ALnQ417, eric899.
• myst-6 for being too enslaved to test.
• Alexdat2000 for translating the statements into russian.
• MikeMirzayanov and KAN for codeforces and polygon.
• You for participating.

Score distribution: $$$500 - 1000 - (1250 + 1000) - 1750 - 2500 - (2250 + 1750)$$$

UPD: Editorial

UPD2: Congratulations to the winners!

From Div. 2:

1. RGB_ICPC3

2. ljw01

3. paulo.pr

4. HusseinFarhat

5. happyhush

From Div. 1 + 2:

1. potato167

2. Geothermal

3. A_G

4. arvindf232

5. maspy

Hello, Codeforces!

I am very excited to invite you to our contest Codeforces Round 1059 (Div. 3), which starts on Oct/17/2025 17:35 (Moscow time). You will be given $$$2$$$ hours and $$$15$$$ minutes to solve $$$8$$$ problems.

The problems were authored and prepared by wakanda-forever, wuhudsm, tridipta2806 and frostcat.

Note that at least one of the problems will be interactive. So if you are unfamiliar with them, please read the guide for interactive problems before the contest.

The round will be hosted by the 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 — rank will be determined by the number of problems solved, followed by penalty; wrong submissions will incur the usual penalty of 10 minutes, following the rules of educational rounds.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by the 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.

We would like to thank:

• cry for beautiful coordination.
• shorya1835, Divine_Spark and Krishbansal333 for proposing problems that later weren’t included in the final set.
• Dominater069 for LGM testing.
• __baozii__ for red testing.
• Friedrich, mayank69goel, shorya1835, aastik231205, reirugan, Intellegent, 18o3, Ming_Xu, Proof_by_QED, efishel and Arpa for orange testing.
• Edeeva, Prady, friedel, Forge, macaquedev, pop and omegaphi for purple testing.
• RustyGrill, Eikyu, HackerGupta069, DivinePunishment, Darsh_Jain, expertaq, Kushi, Krishbansal333, kingbass and chromate00 for blue testing.
• Trace_X1729, sanju77 and Maroon5_sugar for cyan testing.
• santaclaus67 for green testing.
• MikeMirzayanov and KAN for the great platforms.

I wish you the best of luck, and I hope you enjoy the problems!

UPD: Editorial

Hello Codeforces!


We are pleased to announce the start of the Yandex Cup 2025 Championship!

This year, we still have 6 tracks and a prize fund of 12 million rubles:

• Algorithm❤️
• Machine Learning
• Backend
• Analytics
• Frontend
• Mobile development

Let's talk in more detail about two directions:

Algorithm ❤️

An important change this year: we ask all participants of the qualification stage (last year it was called the semi-final) who are applying for the finals to arrange proctoring. After the qualification is completed, a window will appear in the participant's personal account, where you will need to send a link to proctoring.

Machine Learning

This year we decided to make the track more interesting. We have three pieces of news:

• from this year, the Machine learning track, like the Algorithm track, becomes international;
• schoolchildren from Russia aged 14 to 18 can participate in the track;
• the format of the competition is changing.

The new format of the Machine Learning track:

The qualification stage will last 22 days — from October 15 to November 2, inclusive. Participants will be offered three tasks:

• Autonomous Driving camera sensor image generation.
• STEM problem illustrations Q&A with VLMs.
• Large Language Models hallucinations robustness.

Restrictions: each participant can submit two submissions per day with a limit of 1 GPU/hour. We will publish detailed rules of the track on the direction page on Tuesday.

The final stage is a five-hour contest with tasks in the ioai-format.

Dates of the championship in 2025

Trial round

This year, we have made some changes to the qualifying stages. All stages of the championship in all directions will be held on our testing system Yandex Contest. This year, our colleagues from Yandex Contest have significantly updated the user interface. We do not want the unfamiliar interface to prevent participants from achieving the desired results. Therefore, instead of the usual qualification stage, we will hold a trial round with tasks from previous years. The trial round will not be taken into account in the overall standings, but we recommend taking part in it to get to know the new interface.

Dates of the trial round: October 20–29 (format: virtual contest).

Qualification round (former semi-final)

The qualification round will be held on November 2. The start of the contests is at 12:00 (GMT+3) and 17:00 (GMT+3) for the «Algorithm» and «Analytics» tracks. The duration depends on the chosen track.

Final round

The following will reach the finals:

• the top 20 participants in the Algorithm, Backend, Analytics and Machine Learning directions;
• the top 10 participants in the Frontend and Mobile Development directions;
• the top 10 participants in the Juniors track in the Algorithm, Analytics and Machine Learning.

The final of the competition will be held in Istanbul, Turkey, from December 5 to December 7. We will cover all expenses related to the travel and accommodation of the finalists.

We have prepared a detailed schedule for you in the form of a table here

Or you can follow the dates on CLIST

See you soon!

Hello, Codeforces!

We gladly invite you to participate in Codeforces Round 1058 (Div. 1, Div. 2), which will be held on Oct/12/2025 17:35 (Moscow time)! You will be given $$$\mathbf{2.5}$$$ hours to solve $$$\mathbf{6}$$$ or $$$\mathbf{7}$$$ problems (depending on your division). One problem will be divided into two subtasks.

The problems were authored by wuhudsm, Proof_by_QED and chromate00. We have put so much effort (and time) into this contest, and we hope you will enjoy it!

Do note that for both divisions, at least one of the problems will be interactive. So if you are unfamiliar with them, please read the guide for interactive problems and get yourself ready.

Our team would like to thank the following people:

• TheScrasse for coordinating the round and believing in us for such a long time;
• Alexdat2000 for translating statements in this and every other contest;
• cry and sum for earning the "professional relaxer" title by not proposing problems;
• satyam343, BurnedChicken, zeemanz for VIP testing;
• Um_nik for shortly taking a look at the problemset;
• A_G, _istil, sammyuri, fextivity, cadmiumky, Dragos, IBory, szilb, awoo, rhombus, efishel, Intellegent, turska, adamant, beaaaan, spike1236, ArshiaDadras, qwexd, reirugan, rewhile, harshith_04, macaquedev, Edeeva, IvanBorquez, ProofByContradiction_, DivinePunishment, larush, tin.le2, ymwang, Non-origination, SpyrosAliv, and ALnQ417 for testing the problemset and helping us improve it;
• MikeMirzayanov and KAN for great platforms Codeforces and Polygon;
• and last but not least, You for participating!

And now, the score distribution.

Division 1:

Good luck, and I hope you find enlightment from the problemset!

UPD: Editorial is uploaded here.

Also UPD by chromate00: I sincerely apologize about the weak pretests of problem 1B/2E. I have greatly underestimated the runtime and memory usage of the worst solutions, while still wanting to be generous about slower solutions. This has led to weak tests during contest. Deeply sorry about the bad contest experiences affected by this.