Hello, Codeforces!

I and ooaa are excited to invite you to participate in Codeforces Round 922 (Div. 2), which will take place on Jan/30/2024 17:35 (Moscow time).

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

You will be given 7-8 problems and 2 hours to solve them. We recommend you to read all the problems. 1 or more interactive problems may occur in the round, so we suggest to read this post.

We would like to thank:

• Akulyat for the excellent coordination of our round.
• wuhudsm for finding that the previous C has already occured in one of the rounds.
• A_G, bashkort, orz, Andreasyan, green_gold_dog, zwezdinv, EJIC_B_KEDAX, Kihihihi, makrav, sam571128, Undying, htetgm, wuhudsm, kovir_aleksey_korroy, JustNik77, Chaska, Murinh0, leoper and Ileonov for testing and valuable feedback.
• MikeMirzayanov and geranazavr555 for the excellent Codeforces and Polygon platforms.
• You, for participating in this round.

We wish you good luck and high rating!

UPD. Score distribution: $$$500 - 1000 - 1250 - 2000 - 2500 - 3000 - 3250$$$.

UPD2. Congratulations to the winners!

Div. 2

1. alice_ssoi

2. JaredGoff

3. ppltn

4. sunc_mgu_govno

5. 1926_yes

Div. 1+2

1. arvindf232

2. SSerxhs

3. alice_ssoi

4. natofp

5. JaredGoff

Congratulations to the first solves as well!

• А. EyadBT
• B. __jk__
• C. Golovanov399
• D. thisisnotaclone
• E. WLZ
• F. tute7627
• G. wsyear

UPD3. Editorial.

Hi Everyone :)

I would like to invite you to my first Codeforces Round, which I set with my friends JaySharma1048576 and mexomerf — Codeforces Round 921 (Div. 1) and Codeforces Round 921 (Div. 2) which will be held on Jan/27/2024 17:45 (Moscow time). This round will be rated for both divisions.

Both divisions will be given 6 problems and 2 hours to solve them.

One of the problems may be interactive. So, you are advised to refer to the guide on interactive problems in case you are not familiar with them.

We would really like to thank:

• Aleks5d for coordinating our round.
• jtnydv25, dario2994, IceKnight1093, oursaco, satyam343, Riladavin, magga, peltorator, _Enigma__, Makcum888, MisterReaper, htetgm, 18o3, sezal, alwyn, somplz, nor and kevinsogo for testing and improving the problems.
• abhidot for listening to our problems even before we proposed them.
• MikeMirzayanov for the amazing Codeforces and Polygon platforms.
• You for participating.

Good luck, have fun!

UPD: Scoring Distribution

Div. 1: $$$500 - 1000 - 1500 - 1750 - 2500 - 3000$$$
Div. 2: $$$500 - 1000 - 1250 - 1750 - 2500 - 3000$$$

UPD: Here is the editorial

UPD: Congratulations to the winners

Div. 1:

1. jiangly
2. maroonrk
3. Benq
4. gamegame
5. maspy

Div. 2:

1. kto_eto
2. fractum_locum
3. okok
4. beiyuli
5. BabaVoss

First solves -

Div. 2:

Div. 1:

Hello, Codeforces!

If you're developing problems in Polygon, you might like this image to attract attention.

For the new members of the community, I would like to remind you that Polygon (https://polygon.codeforces.com/) is a system developed and maintained by Codeforces for preparing programming problems. It is there that authors and coordinators develop all the problems for the rounds. Moreover, I believe a significant (large?) portion of the problems for other competitions is also developed there: various stages of ICPC, national competitions of different levels, educational problems for various courses, etc. In 2023, more than 50000 problems were prepared in Polygon (only those for which a package was compiled are counted)!

We often implement such improvements in Polygon that make the process of preparing a problem more reliable. These often include various automatic warnings and tips for problem developers and/or coordinators.

Today I want to talk about two recent such innovations in Polygon.

Hello Codeforces!

On Jan/18/2024 17:35 (Moscow time) Educational Codeforces Round 161 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

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, Roman Roms Glazov and me. Also, huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Big thanks to the testers shnirelman and Minder for their valuable advice and suggestions!

Good luck to all the participants!

UPD: Editorial is out

Hello! On Jan/15/2024 17:35 (Moscow time) will start Codeforces Round 920 (Div. 3), the next Codeforces round for the third division.

The round was coordinated by Vladosiya, and prepared by me and the students of Neapolis University Pafos: Vitaly503, goncharovmike, ikrpprppp, step_by_step.

Thank you very much Alexdat2000, dan_dolmatov, fastmath, FBI, Nickir, nikhil97agra, pavlekn, PMiguelez, SashaT9, senjougaharin, Sergey140146659, Sparrow_Guo, Toy_mouse, vladmart for testing the round.

As usual for the third division rounds:

• there will be 6-8 tasks in a round
• round duration is 2 hours 15 minutes
• the round follows the ICPC rules, penalty for an incorrect submission is 10 minutes
• round is rated for participants with ratings up to 1600
• after the round there will be a 12-hour open hacking phase

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 behaviour. 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.

Good luck to all!

UPD: Editorial

The Registration for the 46th Petrozavodsk Programming Camp is open.

THE CAMP WILL BE HELD ONLINE from January 30 to February 06, 2024.

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/2024w/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.

UPD: Also this year, we decided to simultaneously organize the second division for Russian-speaking participants. The second division is aimed to help college students prepare for participation in regional Olympiads and ICPC quarterfinals/semifinals. There will be lectures, themed contests, as well as the usual competitive contests.

Contact Information

• Contact the organizers: [email protected]
  
• Website: camp.icpc.petrsu.ru
  
• Group in VK: vk.com/camp_acm_petrsu
  

Hello Codeforces!

omeganot and I are excited to invite you to participate in Codeforces Round 919 (Div. 2) which will start on Jan/13/2024 17:35 (Moscow time). You will be given 2 hours to solve 6 problems. One of the problems is divided into 2 subtasks.

This round will be rated for participants of Division 2 with a rating lower than 2100.

We would like to thank

• Artyom123 for his epic coordination and also for translating the problem statements!
• A_G, PurpleCrayon, Yam, Andreasyan, oursaco, hyforces, Apple_Method, GusterGoose27, null_awe, awesomeguy856, lunchbox, jli505, Lemur95, ocasu, EmeraldBlock, EnDeRBeaT, cry, htetgm, SriniV, nonrice, mark, thehunterjames, ETL, AndrewPav, ForgottenDestiny, lazipotato, dutin, and Saq56 for testing the contest and providing valuable feedback.
• MikeMirzayanov for the amazing Codeforces and Polygon platforms.
• You for participating!

The score distribution is $$$500 - 1000 - 1500 - 2000 - 2250 - (2500 - 2500)$$$.

We hope everyone will enjoy the round!

UPD 1: Editorial

UPD 2: Congratulations to our winners and first solves!

Hi everyone!

Sponsored by

After successful camps last year (winter wrap, fall wrap), we are happy to announce that Osijek camp will be returning on 17.-25. February 2024 — just in time to prepare for the World Finals in... Maybe this spring? As well as several regional contests throughout the fall. 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.

If you want to get a feel of the contests, two contests from the last edition will be featured in Universal Cup contests soon:

1. Estonia contest, scheduled on 2024.01.20.
2. Delft contest, scheduled on 2024.02.03.

After Universal Cup rounds, the contests will also be uploaded to Codeforces gym.

Details

Participation fee for onsite participants is 150€ per person. It does not include regular meals, travel or accommodation. Some further details about location, travel and food options can be found on the website.

If you want to participate, but are unable to come onsite, we offer a reduced fee of 100€ per person for online participation. It is also possible to reduce fees individually if you are unable to attend some of the contests. This will be handled on a case-by-case basis.

We support and empathize with those affected by the ongoing war in Ukraine, therefore we offer a 100€ discount for affected individuals and teams affiliated with Ukrainian institutions. In other words, the fees would be 50€ and 0€ per person for onsite and online participation correspondingly.

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 other starting times.

Most of our contests are fresh and developed for this 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 (and your participation fee will be reduced accordingly). We will privately contact participants who might be affected. Based on feedback, we will have a silence period until the end of World Finals 2023, during which camp materials will not be released to the public. Therefore, we ask participants to not discuss the problems in public until that date.

Participants

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

We ask you to register before February 9 if you want to participate online and before February 3 if you want to participate onsite.

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 fill the form here, so that we can send an invitation. Thanks!

Problemsetters

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

• qwerty787788 — ICPC 2015 World Champion, Google HashCode 2019 and 2020 winner, CodeChef SnackDown 2016 and 2019 winner.
• antontrygubO_o — author of 1188B - Count Pairs.
• jeroenodb — Codeforces International Grandmaster, Computational geometry enjoyer. NWERC 2023 silver medalist.
• 998kover — IOI gold medalist, problemsetter for IZhO and data structure enjoyer.
• TheScrasse — Codeforces International Grandmaster, SWERC 2023 silver medalist, Codeforces coordinator.
• KLPP — Codeforces International Grandmaster, SWERC 2023 silver medalist, IOI silver medalist.
• Lebossle — Codeforces Grandmaster, problemsetter for ICPC Latin America 2021+.
• adamant — Codeforces Grandmaster, maintainer of cp-algorithms.com, Osijek camp organizer, author of over 60 competitive programming problems.
• gen — ICPC 2012 and 2014 world finalist, Google Hashcode 2017 finalist, coauthor of 7 Codeforces contests.
• de_sousa — SWERC 2023 silver medalist.
• flamestorm — MIT student, author of over 50 competitive programming problems.

... And others. We would also like to thank Um_nik and errorgorn for their help with reviewing problem proposals.

You can find more details about contest rules and technical setup on the website.

Sponsors

Last but not least, we would like to say special thanks to our sponsors, who make the camp possible. If you are interested in sponsoring next editions of the camp or have any questions, please feel free to reach out at ocpc (at) mathos (dot) hr.

We would also like to thank Codeforces for guidance and promoting this announcement to the main page, eolymp for providing us an online judge for the contests and the School of Applied Mathematics and Computer Science of the University of Osijek for all their organizational support and providing us a physical location to conduct the camp.

Finally, we kindly thank ICPC foundation for their help and support.

Hello, Codeforces!

For the new members of the community, I would like to remind you that Polygon (https://polygon.codeforces.com/) is a system developed and maintained by Codeforces for preparing programming problems. It is there that authors and coordinators develop all the problems for the rounds. Moreover, I believe a significant (large?) portion of the problems for other competitions is also developed there: various stages of ICPC, national competitions of different levels, educational problems for various courses, etc. In 2023, more than 50000 problems were prepared in Polygon (only those for which a package was compiled are counted)!

Large language models are becoming an increasingly integral part of our lives, taking over routine and monotonous tasks.

With their help, problems created in Polygon will now have fewer typos and incorrect language constructions.

We have recently implemented three features in Polygon to ease routine tasks:

• Translation of solutions into another programming language
• Translation of problem statements into another language
• Advice on improving the texts of problem statements

All these features operate on request and typically take 30-120 seconds for a response from the AI service (currently, only OpenAI GPT in our case).

While waiting for translations of solutions and statements is acceptable, waiting for advice on improving text was too tiresome.

I recently developed several problems and, despite my experience in writing statements (and even having the highly recommended Grammarly plugin in my browser), the automatic advice tool for improving text helped enhance them.

Another example: I checked the working versions of the Hello 2024 problems about a day before the round started and took the time to manually launch the edit prompter. In most (almost all?) problems, it indeed suggested errors or deficiencies in English/Russian. The corrections were minor, but why leave mistakes if they can be fixed?

Indeed, such a tool can greatly improve the grammar of statements, but using it on demand was tiresome.

As a result, I implemented background processing of the problem statements to simplify and speed up the application of this feature. Now, Polygon analyzes problem statements in the background to find shortcomings. If any are found, you will see a similar block in the problem's sidebar.

This block might not appear immediately upon changing the statement, as processing a request to the AI service usually takes tens of seconds.

Clicking on the review link will open a tool for merging changes.

This is a synthetic example. I made a few typos in the statement of my old problem. I should note that even the Grammarly plugin didn't catch all of them.

I circled one of the triangles. Click on them to transfer the proposed changes (on the right) to the text of the statement (on the left). You can only transfer for a whole paragraph at a time (that's how the tool works), but you can manually correct the left if you want to transfer part of the changes or modify them.

At the bottom of the form is a Save button that will save the updated statement.

I hope that authors and coordinators will not neglect this feature and that there will now be fewer typos and language errors in statements.

I would like to note that I see no reason to worry about data leakage when processing statements with the AI service. For example, OpenAI explicitly states that data from API requests cannot be used for training: https://help.openai.com/en/articles/5722486-how-your-data-is-used-to-improve-model-performance. After all, we've been googling problem ideas for many years to ensure the problem is new. It seems to be a similar case.

However, if you are still concerned and want to explicitly disable this feature, it can be done:

• For a problem: via the Advanced link on the General info tab.
• In user settings: disable this feature for all new problems you create.

Thanks for reading! Stay tuned for more updates.

Hello.

Today I removed the account zh0ukangyang from the rating, after first nullifying its results in the Pinely Round 3 (Div. 1 + Div. 2) and banning it.

I would like to remind you again: Codeforces insists on the policy of using a single account. Creating and using additional accounts violates this rule. In an ideal world, each Codeforces account corresponds to one specific person.

Sometimes additional accounts are created for official, usually collective purposes (writing a post on behalf of a company, etc.). In such cases, these accounts do not participate in rated rounds and we do not pay attention to them unless there is some abuse of Codeforces resources.

Unfortunately, it is difficult for us to enforce this rule in almost all cases. But I urge you to respect the rules. Please remember that by registering for any rated contest, you confirm that you are participating with your only account. If this is not the case, then you are violating the community rules. Do not do this. By breaking the rules, you automatically agree that punishment may be applied to you.

In cases where rule violations significantly affect the ratings of other participants, we may take drastic measures. Remember, with great power comes great responsibility.

In this case, zh0ukangyang was at the top of the ratings, occupying high places in the rounds.

What should you do if you already have several accounts and want to stop breaking the rules? You should not write to us with a request to delete accounts or transfer data from one account to another. All you need to do is simply stop participating from all accounts except one. Change the password to a random one and do not log into the account anymore.

For participants at the very top (somewhere in the top 50 of the ratings), we are ready to manually deal with the situation and exclude illegal accounts from the rating.

M.