Hello, Codeforces!

I am really excited to invite you to Codeforces Round 763 (Div. 2) on Dec/28/2021 16:35 (Moscow time)! The start time is unusual, so please pay attention.

All the problems were authored and prepared by me. I would like to give special thanks to everyone who made this round possible:

• KAN for excellent coordination with a lot of valuable advice!
• KAN again for translation of statements!
• tdpencil, Stepavly, Supermagzzz, minhcool, snowysecret, generic_placeholder_name, QuangBuiCPP, thenymphsofdelphi, PurpleCrayon, xuanquang1999, vinfat, hieplpvip, tourist, Lihwy, flamestorm for testing and valuable feedback!
• MikeMirzayanov for great Codeforces and Polygon platforms!
• You, for participating!

The round consists of 5 problems and you have 2 hours to solve them.

Wish you good luck and high ratings!

UPD0: The score distribution 500 — 1000 — 1750 — 2500 — 2750.

UPD1: Congratulation to the winners of the round!

Div. 2

1. wanyuezaifengli
2. ZhuJianfeng
3. proton1126
4. qazsxdew
5. Hayasaka

Div. 1 + 2

1. heno239
2. Geothermal
3. Vercingetorix
4. dorijanlendvaj
5. wanyuezaifengli

UPD2: The Editorial is out!

Hope that you guys enjoy the rounds, and thank you again for participating! <3

Hello Codeforces!

On Dec/27/2021 17:35 (Moscow time) Educational Codeforces Round 120 (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, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov, Roman Roms Glazov 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!

Oh yes, 2021 ends! I recently realized that 2022 is pronounced like "2020 too". Not that. I want a completely different year!

Anyway, we did a nice job this year. I hope we have pleased you with interesting problems. Thanks to the round coordinators and writers! You make our community richer. Please make us happy in 2022!

I wish you all interesting tasks and brilliant solutions! I wish you error-free code and wish us only rated rounds :-)

Hello, 2022!

And we have traditional gifts!

Change Handle Feature

Hurry! Only until the 10th of January, you can change your handle (but only once)! Note that it will be possible to roll back the changes or change the handle again only after a year. Be careful what you wish for.

You can change your handle to the new one which wasn't used before by anybody or which was used by you before. The links to a profile page with an old handle would automatically redirect to the actual profile.

Again, this year if you took part in at least 10 rounds you can request a handle of an inactive participant. It means that the participant should have a period of activity on Codeforces of at most 180 days, this period should be in 2019 or earlier. The inactive participant can't have posted comments, messages, and so on. It can't take part in more than 2 contests. It will be automatically renamed and informed by email. A user has the opportunity to request back his/her handle: in this case, we will roll back the change and return your previous handle to you. If you can't change your handle to another, it means that some requirements don't meet. Please do not ask me to do something with it. Especially, I do not like requests like "this is my second account, I took an interesting handle myself". I'm not Santa Claus.

Talking about handles I always
reminisce the following story. Once a user wrote me the 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 the profile setting. Happy New Year!

Happy Holidays!

On Dec/24/2021 17:35 (Moscow time) we will host Codeforces Global Round 18.

It is the sixth round of a 2021 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The presents for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The presents for the 6-round series in 2021:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2021 supported the global rounds initiative!

The problems were written and prepared by the hard-working elves Monogon, BledDest, and PurpleCrayon.

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

• The fabulous reindeer awoo, QuangBuiCPP, manish.17, Lyde, penguinhacker, Maksim1744, BucketPotato, magnus.hegdahl, ecnerwala, ItayOtto, ijxjdjd, actinium16, gamegame, kpw29, Um_nik, TadijaSebez, and AliShahali1382 for testing the round and providing valuable feedback to the problems!
• antontrygubO_o, the most famous reindeer of all!
• adedalic, for excellent coordination of the round!
• Saint Micholas Mirzayaclaus, MikeMirzayanov, for the amazing Codeforces and Polygon platforms!
• All the nice boys and girls who participate!

You will have 2.5 hours to solve 8 problems.

UPD: The scoring distribution: 250 — 1000 — 1750 — 2250 — 2750 — 3000 — 3750 — 4000

UPD: Editorial is out!

Good luck, have fun, and stay off the naughty list!

Hello! Codeforces Round 762 (Div. 3) will start at Dec/20/2021 17:35 (Moscow time). You will be offered 7-8 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 ACM-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.

You will be given 7-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) 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.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of our work. Problems have been created and written by ITMO University teams: MikeMirzayanov, MisterGu, myav, Gol_D, Aris, senjougaharin, me Vladosiya and SGU student Brovko.

Also many thanks to Geothermal, Rafbill, Sugar_fan, mango_lassi, hitonanode, Resende, Igorjan94, CtrlAlt, KerakTelor, FlakeLCR, MatheusMonteiro, Loolo, kocko for testing the contest and valuable feedback.

Good luck!

UPD 1: The opinion of the testers about the order of problems turned out to be so heterogeneous that there is no way to be sure about the increase in the complexity of problems in the set. We advise you to read all problems.

UPD 2: If you are a schoolchild from the Saratov region, then please refrain from participating in the round. One of the problems may be familiar to you. Thanks!

UPD 3: Editorial

Hello Codeforces!

On Dec/18/2021 18:35 (Moscow time) Educational Codeforces Round 119 (Rated for Div. 2) will start. Please, note the unusual start time.

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, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov, Roman Roms Glazov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Our friends at Harbour.Space also have a message for you:

Hello once again, Codeforces!

Almost 5 months have passed since we organized the Harbour.Space Scholarship Contest 2021-2022. It’s been quite a tough challenge with more than 15,000 participants. However, we were able to select the ones who were ready to take the opportunity and join Harbour.Space this year. In addition to the contest, we carefully reviewed all scholarship applications and awarded a total of 11 students.

We would like to introduce you our Competitive Programming Scholarship Winners who have already arrived to Barcelona:

aniervs, MaksymOboznyi, 244mhq, Meijer, bthero,amanbol, DimmyT, 998kover

We are looking forward to achieving incredible results with our new ICPC teams. One of them, Harbour.Backspace (MaksymOboznyi, 244mhq, 998kover), has already finished in 3rd place during Moscow Workshops. We wish them the best in the upcoming contests.

As usual, we are always excited to see Codeforces participants as our students here at Harbour.Space

UPD: Editorial is out

Hello, Codeforces!

I am happy to invite you to Codeforces Round 761 (Div. 2), which will take place on Dec/16/2021 16:35 (Moscow time). The round will be rated for participants with rating lower than 2100. Notice the unusual starting time.

All the problems were authored and prepared by me. The round wouldn’t be possible without these people:

• Artyom123 for excellent coordination and translation of statements.
• KAN for help with round preparation.
• arvindf232, physics0523, SecondThread, Igorbunov, kevinxiehk, generic_placeholder_name, Kotehok3, minhcool, anthony123, Elison, shishyando, SlavicG, Absyarka, erniepsycholone, dbsbs, lomienyeet for testing and valuable feedback.
• Again, arvindf232 and generic_placeholder_name for providing solutions to a problem that are better than the author’s solution.
• Again, kevinxiehk for submitting many different solutions to a problem.
• MikeMirzayanov for great Codeforces and Polygon platforms.
• You, for participating!

You will have 2 hours to solve 5 problems, one of which is divided into two subtasks. One of the problems is interactive, please see the guide of interactive problems if you are not familiar with it.

Wish you good luck and high ratings!

Here is the score distribution: $$$750-1000-1500-(2000-1000)-3000$$$.

The editorial is here: click.

UPD: Sorry but there is a checker bug in problem E. All submissions of problem E will be rejudged soon.

UPD2: Rejudge done, the round remains rated.

Congratulations to the winners (will be updated after system tests):

We invite ML students and specialists from all over the world to take part in the International Data Analysis Olympiad. HSE University and Yandex are organizing it for the 5th time, and the Otkritie bank will be our platinum partner this year.

Since it’s our first anniversary, we decided to change the format: students and ML specialists are divided into two separate divisions. Only students are able to join the main competition — the Student Division. All others can join the Open Division to participate hors concours (for their own interest).

Traditionally, the first stage’s task will be given by the Laboratory of Methods for Big Data Analysis (LAMBDA, HSE University). It will be about predicting the properties of two-dimensional crystals of various configurations. The task for the Finals will be provided by the Otkritie bank. The Olympiad includes two stages:

Online Stage (1-28 February 2022):

• Track 1: Traditional machine learning competition on Yandex.Contest platform. You will need to make new predictions and upload them to the automatic verification system.

• Track 2: Come up with a solution for the same problem, keeping within a rigid framework of time and memory used.

Final (16-17 April 2022, Moscow):

• top 30 teams according to the Online Stage results will be invited to the Online final.

• In the final 36 hours of the competition, participants will try not just to train the model, but to create a full-fledged prototype, which will be tested both in terms of accuracy and performance.

Registration is open till February 13: https://idao.world/

Hello, Codeforces!

On Dec/14/2021 17:35 (Moscow time) the Codeforces Round 760 (Div. 3) will start. This is a usual round for the participants from the third division. The round will contain 8 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.

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 8 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 Brovko, shnirelman, Lankin, awoo and me. We would like to thank the testers of the round: vovuh, Nil_Sinyaev, IsaacMoris, altynai, MarcosK, osylai, ZulaMostafa, nondeterministic, mumumucoder, peroon and kocko.

And, the last but not the least, thanks to Mike MikeMirzayanov Mirzayanov for Codeforces and Polygon systems!

Good luck in the contest! I hope you'll enjoy solving the problems we have prepared.

UPD: The editorial is out.

Hi all!

This weekend, at Dec/12/2021 18:15 (Moscow time) we will hold Codeforces Round 759 (Div. 2, based on Technocup 2022 Elimination Round 3). They are based on problems of Technocup 2022 Elimination Round 3 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup website and take part in the Elimination Round.

The Div.2 edition is open and rated. Register and enjoy the contests!

• The round authors are: Denisson, antonis.white, dimatimoshin23, napstablook, kirill.grachoff
• Thanks Makcum888, snowysecret, stevancv, wxhtzdy, and ijxjdjd for testing.

Have fun!

UPD: congratulations to the winners!

Technocup 2022 - Elimination Round 3

1. LeoPro
2. princebelkovetz
3. DDima
4. pelmenner
5. abdula-mon-fon-alibaba-A

Codeforces Round 759 (Div. 2, based on Technocup 2022 Elimination Round 3)

1. Maria_Akizuki
2. maxlevel_spyofgame
3. zhaojianmin
4. FlameDragon
5. Shawn

The editorial is published.