Heyo Codefoworcers!

vgoofficial and I are very delighted to invite you to participate in Codeforces Round 971 (Div. 4), which will start on Sep/03/2024 17:35 (Moscow time). There will be $$$7$$$ problems, with one split into three subtasks, to be solved in $$$2$$$ hours and $$$30$$$ minutes. We encourage you to participate and hope you have fun, regardless of your division!

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

• 5-8 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 (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 his awesome coordination and mesanu for reviewing the problemset once again.

• Our MVTs (Most Valuable Testuwuers), satyam343 and Dominater069, for their dedicated contributions.

• The rest of our army of testuwuers: omeganot, nskybytskyi, awesomeguy856, 18o3, Lilypad, chromate00, Sacharlemagne, ntarsis30, Prady, Non-origination, yash_9a3b, ETL, Orange905, MatthewC3297, mathtsai, macaquedev, jcai972, and cj8450.

• MikeMirzayanov for all that jazz.

01100 00000 11000 10011 00111 01000 10010 01001 01110 10100 10001 01101 00100 11000 01011 00100 00000 00011 10100 10010 10010 10011 00000 10001 10110 00000 10001 00011

UPD: The round will be unrated, even though m1.codeforces.com, m2.codeforces.com, and m3.codeforces.com were functioning correctly. While there were issues on the main site (which lasted more than an hour), no participant was able to view the leaderboard, ask a question, or receive an answer.

Editorial

Hello Codeforces!

I am pleased to invite you all to participate in Codeforces Round 970 (Div. 3), which will start on Sep/01/2024 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 the first 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 and testing the round.

• Vladosiya for beautiful coordination and helping in preparation.

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

• gmusya, Axial-Tilted, chen_zexing, Mr.Pie, XYZ_Herry, gvancak, Layk, CLown1331 and aboodsalman04 for testing and useful feedback.

Good luck!

UPD:

Editorial has been published.

Hello,

As you may have already noticed, tourist has reached the symbolic milestone of 4000 rating points. This is the first time in the history of competitive programming. I, personally, and the entire Codeforces team, congratulate Gennady tourist Korotkevich on this incredible achievement!

Right now, we have assigned a new rank “Tourist” to the 4+ rating. This highlights the uniqueness of the moment!

However, in the future, I would like to change this name to something a bit more neutral (or leave it Tourist?). Would you help me with this?

I’d appreciate your cool suggestions in the comments!

Here are a few options from me. Please, vote:

• Epic Grandmaster
• Ultimate Grandmaster
• Godlike Grandmaster
• Tourist
• 4K Grandmaster
• Grandmaster 4K
• Legendary Grandmaster 4K
• Joke option: Ultra HD Grandmaster
• from Tlatoani: Champion

Feel free to propose your own options and add (likes:n) (use square brackets instead of round), where n is an integer starting from 1, to allow for voting.

It's been a long day without you, Codeforces!

We are glad to invite you to take part in Codeforces Round 969 (Div. 2) and Codeforces Round 969 (Div. 1), which will start on Aug/30/2024 17:35 (Moscow time). You will be given 6 problems and 2 hours and 30 minutes to solve them in both divisions.

The problems are authored by LMydd0225, tzl_Dedicatus545, _FJqwq, Ternary_Tree_ and me wyrqwq and mostly prepared by LMydd0225. One of the problems is also prepared by DitaMirika.

We would like to thank:

• Artyom123 for his intelligent coordination, and for Russian translation.
• arvindf232, dXqwq, A_G, Atomic-Jellyfish, N_z__, Tony2_CF, abc864197532, PEIMUDA, hyman00, yuanruiqi, Imdie, _Purslane_, superyijin_txdy, SATSKY_2024target_IGM, Error_Yuan, WRKWRK, cfhj, Clan328, celin, Misuki, Romy67, misorin, yangchang, Fish_and_Chips, Yoav, turgon314, Tricopter, oloy, Lastiy124, Leonardo_Paes, flakes24, deneribeiro10, lhzawa for testing.
• MikeMirzayanov for Codeforces and Polygon platforms.

Hope you will enjoy the problems!

Score Distribution:

• Div. 2: $$$500 - 750 - 1000 - 1500 - 2250 - 2750$$$;
• Div. 1: $$$750 - 1250 - 1500 - 2000 - 2500 - 3000$$$.

badges$$$^\dagger$$$ of the authors:

$$$^\dagger$$$: Began in 2022 at NOI Shanghai, Badge Exchanging has been an activity popular among Chinese CPers. The host school for NOI 2022 decided to print badges containing the avatar of contestants for the contestants, and one can exchange his or her badge with another. The collection of one's badges (of other CPer's avatars) shows the group of CPers that he has met and even made friends offline. It has achieved great success. And since then, it has been a tradition for years.

UPD: Congratulations to the winners!

Div. 1:

1. tourist (Updated, and congrats!)
2. jiangly
3. ecnerwala
4. Radewoosh
5. Kevin114514

Div. 2:

1. mkrukov07
2. temp6
3. wjq1234567
4. bingpao
5. AuSquare (It seems that the rank 5 was banned? So let's move on to rank 6!)

The Editorial is out. You can also download Simplified Chinese Editorial in the contest material of the Div. 1 part of the contest.

Hello!

We are starting to test the long-awaited feature of non-rated registration for rounds. Here’s the plan: we will first test this feature in Testing Round 19 (Div. 3). Then, we will apply this innovation for ICPC-like rounds (Div. 4 Rounds, Div. 3 Rounds, Educational Rounds). After we have tested the feature in ICPC-like rounds, we will start using it in other types of rounds as well.

Here’s how the feature works:

• When you register for a round (if it is rated for you), you can choose non-rated registration if you do not expect to perform at your best (for example, if you might be interrupted during the round).
• You can change your registration type (rated or non-rated) BEFORE THE ROUND STARTS. Once the round starts, you cannot change your registration type.
• If you register for a round after it has started, you will automatically be registered as rated (if the round is rated for you). In other words, you will not be given the option to register as non-rated.
• After the round, the rating will be updated only for those who participated in the round and had a rated (regular) registration.

During the round, you will not be able to see whether another participant is registered as rated or non-rated. You will be able to find out later by checking if their rating has changed.

We urge you not to abuse this feature in the future and to try to participate in rated mode. Use this option only if you have a valid reason.

Let's test the new feature together: participate in Testing Round 19! We advise you to randomly choose your registration type so that we have both rated and non-rated registrations.

After the round, we will temporarily recalculate ratings to ensure everything works correctly. After that, of course, the rating changes from Testing Round 19 will be removed.

Thank you for participating!

UPD: Thank you all for testing! Share your feedback in the comments. The ratings for this round will be rolled back within a few hours.

(After 3 months) Hello again, Codeforces!

We are glad to invite you to participate in Codeforces Round 968 (Div. 2), which will start on Aug/25/2024 17:35 (Moscow time). You will be given 6 problems and 2 hours to solve them. Two problems are divided into two subtasks.

This round will be rated for participants whose rating is below 2100. Participants with higher rating can participate unofficially.

The problems were authored and prepared by me.

I would like to thank:

• 244mhq for perfect coordination.
• A_G, wutongchun, yeminghan for red testing.
• DisconnectedGraph, small_peter, JWRuixi for orange testing.
• yinhee, QwQwf, Jryno1, sinsop90 for purple testing.
• dieselhuang, WRuperD, CSQ31, gdf_yhm for blue testing.
• liujunyi123, Ender32k for cyan testing.
• ishaandas1 for green testing.
• Our previous testers Um_nik, antontrygubO_o, CharlieV, YuJiahe, Edwin__VanCleef for testing a subset of the problems.
• MikeMirzayanov for the great Codeforces and Polygon platforms.

• You

  for participating!

Scoring distribution: $$$500 - 750 - 1000 - (1000 - 1250) - (1750 - 1000) - 2500$$$.

Good luck & Have fun!

UPD1: Editorial and also Simplified Chinese Editorial are out.

UPD2: Congratulations to the winners!

Div. 2:

1. Empty_Dust
2. cz_yxx
3. Hosen_ba
4. farkon00
5. _minhduccp

Div. 1 + Div. 2:

1. jiangly
2. ksun48
3. kotatsugame
4. Sugar_fan
5. Golovanov399

UPDATE: Some time ago, there was news here that we supported C++23 by installing GCC 14 from the Winlibs project. It turned out that with this method of supporting C++23, some compatibility issues lead to significant performance drops in certain submissions. So, I tried another distribution for GCC 14: the MSYS2 project. It seems that this problem does not occur with it, and now there are no unexpected performance drops. Let's test this C++23 support option together!

Hello, Codeforces!

Together with Vladosiya, we've added support for the 64-bit g++14 C++23. You can find it under the name GNU G++23 14.2 (64 bit, msys2).

If you're using Windows, you can easily install it via our minimalistic package manager, PBOX, by running the command pbox install gcc14-64-msys2.

Thanks to the MSYS2 project! We used the distribution from the official package manager.

Your solutions will be compiled using the following command line: g++ -Wall -Wextra -Wconversion -static -DONLINE_JUDGE -Wl,--stack=268435456 -O2 -std=c++23 program.cpp -lstdc++exp.

Now you can start using C++23 features!

Please note that support for GNU G++23 14.2 (64 bit, msys2) is currently experimental. We invite you to join in the testing and experimentation process. Share your thoughts and experiences in the comments!

Hello Codeforces! (你好, Codeforces!)

Kaey and I are glad to invite you to Codeforces Round 967 (Div. 2) which will start on Aug/20/2024 17:35 (Moscow time).

The contest will last for 2 hours with 5 tasks for you to solve, and 1 task will have subtasks. The contest will only be rated for those with a rating not higher than 2099, but higher rated users are also more than welcome to participate out of competition. There is at least one interactive problem, so please read the guide for interactive problems if you are unfamiliar with them.

Holding the contest would have been impossible without the help from:

• Kaey for supercalifragilisticexpialidocious coordination.
• feecle6418 for providing idea of one of the problem.
• BurnedChicken, cheissmart, SorahISA, WiwiHo, Fysty, Potassium, Emilan, Wayne_Yan, sam571128, Darren0724, HNO2, FoodSheep, Aestivate, jamesbamber, franv, jakao, warner1129, guagua0407, ub33, Bossusuprem, AverageAmogusEnjoyer, _hq8398_, XDEv11, Qualified, temmieowo, kenkenken, ayhan23, DanielMontes, TLE_Automaton, Mohamed_M.M.R, BaoCoder613, alls, Vamperox, Ahmad_OS, AdunAdunov, ciao_gio, baibaiouo, VelajZmaj, pandaa73 for testing and giving useful feedback to make the round better.
• Alexdat2000 for translating the statements to Russian.
• MikeMirzayanov for Codeforces and Polygon.

The score distribution is $$$500 - 1000 - 1500 - 2000 - (2000 - 2000)$$$.

Good luck and have fun!

UPD1: Editorial

UPD2:

Congratulations to the winners:

Div.1 + Div.2:

1. maspy
2. Mangooste
3. kotatsugame
4. Rubikun
5. potato167

Div.2:

1. kkkksc03
2. ThMinh_
3. yifeizhu
4. activedeltorre
5. suuuuuu

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? Check out the CSAI curriculum now. Limited scholarships available — don't miss your chance to study in Europe for free!

On Aug/15/2024 17:35 (Moscow time) Educational Codeforces Round 169 (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 Round 966 (Div. 3) will start at Aug/13/2024 17:40 (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: myav, Gornak40, senjougaharin and Vladosiya.

We would like to thank:

1. MikeMirzayanov for help with ideas and Polygon and Codeforces platforms.

2. FairyWinx, TheScrasse, Be_dos for red testing.

3. irkstepanov, Kirkon, ikrpprppp, Kaey, Bruteforceman for yellow testing.

4. Vitaly503, FBI for purple testing.

5. satyam343, vikram108 for blue testing.

6. trgt26 for green testing.

Good luck!

UPD: Editorial is out.