Hello denizens of Codeforces once again!

After our last two rounds, Yang Liu (desert97) and I (ksun48) are pleased to announce Codeforces Round #492, which will happen on June 24, 2018 at 19:35 MSK. There will be two versions of the contest, one for users in Division 1 and one for users in Division 2. Both versions will have five problems, with three problems shared between the versions.

The round will feature our friend and superstar member of ACM-ICPC team MIT TWO, Allen Liu (cliu568).

The scoring distribution will be visible once the contest begins. As usual, we'd like to thank our wonderful problem coordinator KAN and Codeforces administrator MikeMirzayanov, as well as the rest of the Codeforces staff for keeping this site an amazing place for competitive programming.

This round is in honor of uDebug who have supported Codeforces on its anniversary. Thank you, uDebug! uDebug is an enthusiastic community of competitive programmers who help each other out by answering questions on chat, providing hints and solutions to problems from several online judges, furnishing test input and sharing feedback. On uDebug, you can select a problem you’ve coded up a solution for, provide input, and get the "accepted" output. You can visit it by the link.

Good luck! As always, we encourage competitors to read all the problems.

(also, I seem to have heard some rumors floating around about a special surprise which might be happening during system testing, so keep your eyes peeled!)

Hello!

Codeforces Round #491 (Div.2) will start this Saturday, June 23, 18:35 (UTC+3). This round will be rated for the participants with rating lower than 2100 and other contestants can join it out of competition.

This round problems have a significant intersection with NNSU Programming Contest 2018. Please do not participate in the round if you participated in the NNSU contest or tried to upsolve the problems.

During the round you have to help student Vasya to manage the difficulties caused by the end of the academic year. There will be 6 problems and 2 hours to solve them. If you solve all the problems in 25 minutes you will be able to watch the second half of South Korea — Mexico at the FIFA World Cup.

The scoring is unusual a bit: 500-1000-1250-1500-2000-2750

Great thanks to Mikhail MikeMirzayanov Mirzayanov for the well-known platforms; Nikolay KAN Kalinin — for the help with problems and the round coordination; Mikhail mike_live Krivonosov, Alexey Livace Ilyukhov, Nikita neckbosov Bosov, Andrew GreenGrape Rayskiy and Alexey Aleks5d Upirvitskiy — for the round testing; Arseniy arsor Sorokin — for the statements translation. And good luck to all contestants!

UPD: The round is over, thank you for the participation! The detailed problems editorial will be published in several hours.

UPD: Congratulations to the winners!

Div. 1:

1. nuip
2. krijgertje
3. qoo2p5
4. hohomu
5. neal

Div. 2:

1. adamczh218 — solved all the problems, well done!
2. Daniar
3. Help.me
4. shoemakerjo
5. Toki_Time-Tinker

Hello!

Codeforces Round #490 (Div. 3) will start on June 21 (Thursday) at 14:35 (UTC). You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, 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. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

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

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 participants of the third division, you must:

• take part in at least two 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 my work. Thanks to Mikhail PikMike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

UPD: Also great thanks to step_by_step, kevinsogo and nhho for help in round preparation and testing the round.

UPD2: The results table!

Congratulations to the winners:

Congratulations to the best hackers:

110 successful hacks and 226 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

UPD3: Editorial

Hi, Codeforces! I'm glad to invite everybody to the #489 Codeforces Round, which will be held as soon as tomorrow, on Monday, June 18, 2018 at 19:35. The round will be rated for all participants from the second division (with rating below than 2100). As usually, we will be glad to see participants from the first division out of competition!

Problems for the round have been invented and prepared by us, pupils of Moscow school №2007, Dmitry DmitryGrigorev Grigorev and Fedor ushakov.fedor Ushakov. We want to give thanks to Andrew GreenGrape Raiskiy for his aid in preparing and testing of the problems, to Ildar 300iq Gainullin and to AmirReza Arpa PoorAkhavan who have tested our problems too and to the coordinator Nikolay KAN Kalinin, since our sometimes strange and undeveloped ideas have become eventually the Codeforces round. Also, we say thank you to Mike MikeMirzayanov Mirzayanov for his unbelievable Codeforces and Polygon platforms.

You will receive 5 problems and 2 hours for solving it. During the round you will be helping for an extraordinary girl Nastya, who has been living in Byteland and sometimes receives very strange gifts for her birthday :).

Score distribution will be announced, traditionally, closer to the start of the contest.

We're holding our the first and, I hope, not the last round in Codeforces, so I hope a lot you will like our problems. Please, read all the problems. Anyway, I wish luck and high rating for all the participants!

I'm looking forward your participation.

UPD Score distribution is standart — 500-1000-1500-2000-2500

UPD2 Thank you for your participation in the contest! It's very-very pleasant for me if you like the problems, and I'm sorry if you don't :) I hope the next my contest will be even better, than this. Thank you for all!

List of the winners of the contest:

Div.2

1. sminem

2. guIRELItAr

3. YaDon4ick

4. q-O_O-p

5. pajenegod

Div.1 + Div.2

1. dotorya

2. Benq

3. anta

4. sminem

5. kevinsogo

My frank congratulations for all the winners!

UPD3

Editorial is here

UPD note that the score distribution has changed

UPD2: LHiC found a bug in the author solution of div1-F. We are working on the situation.

UPD3: we found a correct solution for div1-F and both submissions made during the contest pass all the tests against the correct solution. The round remains rated.

Hi, everybody,

Codeforces round 488 for both divisions will take place on Jun/16/2018 19:35 (Moscow time). The round will be 2.5 hours long (which is 30 minutes longer than usual).

The contest is created by NEAR and its friends. NEAR is working on teaching machines to compete in programming competitions. Read our blog post to learn more about the state of the art in the program synthesis today, our vision, and how you can help us bring this vision to reality.

The contest will feature 6 problems for each division, with 4 problems shared across them.

The problems for the contest are from the test rounds hosted on a system JavaBlitz last year. If you participated in any of the JavaBlitz rounds, you shall not participate in this round.

The score distribution in the first division is 500-1000-1000-1500-2250-3000

In the second -- 500-1000-1500-2000-2000-2500

The round is rated for both divisions.

All problems are initially created by myself, Alexander "ItsNear" Skidanov, and by Nikita "neckbosov" Bosov. David "pieguy" Stolp, Alexander "AlexFetisov" Fetisko, Marcelo "MarX" Fornet, Nikolay "KAN" Kalinin and Mikhail "cerealguy" Kever helped tremendously ensuring the high quality of the problems.

As a closing note, we are constantly looking for people to help us label competitive programming data for research. Read more here.

Congratulations to winners!

Div. 1:

1. Um_nik
2. Errichto
3. scott_wu
4. Reyna
5. matthew99

Div. 2:

1. FiveAtomTree
2. shayan.p
3. gauss148
4. kessido
5. codejudge

The editorial is published here. Thanks for your participation!

Here and there, summer's in the air! (I beg your forgiveness, residents of the Southern Hemisphere... > <)

I'm delighted to invite you to Codeforces Round #487 (Div. 2), which starts at Jun/11/2018 16:35 (Moscow time). Please note that the timing is, as usual, unusual.

This is my third time creating a contest from scratch. Along the way can be seen the efforts of: KAN the super-ultra-hyper-mega-meta coordinator, who has reviewed, refined and translated the problems; 300iq, Livace, mike_live, Noam527, RobeZH, and Tommyr7 the super-ultra-great-delicious-wonderful testers, that have populated our collection of solutions; and MikeMirzayanov along with the super-ultra-extreme-awesomazing Codeforces/Polygon team, who have made all these happen in the way it is! Kudos to all of you!

The round will be rated for contestants from the second division, and the first division are welcomed as out-of-competition participants. There will be five problems to work on for two hours. The scoring distribution will be announced later, because of... love.

Despite my illiteracy, I included the stories in the hope that they'll be inspiring to some; feel free to skip them, if you'd like to fully concentrate on problems themselves.

We wish everyone a fun experience and a fair rating. We'll be pleased to have you on the contest!

Gone are the freshness and beauty of springtide, which raises the downheartedness in Mino the poet, as in many other poets. Mino's best friend, Kanno the painter, however, is intrigued by the changing palettes brought about by the seasons. On this day, their journey in search of spring begins...

UPD 1 The scoring is standard: 500–1000–1500–2000–2500. It's however strongly recommended to read other problems if you're stuck, since you may not necessarily find later problems harder. Good luck!

UPD 2 Congratulations to top contestants! Also big kudos to all participants!

Div. 2 Top 5

1. olphe
2. jorik
3. rahuldugar
4. UtahaS3npai
5. espr1t

Overall Top 5

1. olphe
2. mjhun
3. Inner_x_Peace (First to solve E!)
4. kobae964 (_That_ close! Integer division, maybe?)
5. jorik

UPD 3 The editorial is out, see you there!

Hello Codeforces!

On Jun/10/2018 13:05 (Moscow time) Educational Codeforces Round 45 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 extented ACM ICPC rules. 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 7 problems and 2 hours to solve them.

The problems were invented and prepared by Adilbek adedalic Dalabaev, Roman Ajosteen Glazov, Ivan BledDest Androsov, Mike MikeMirzayanov Mirzayanov and me.

Good luck to all participants!

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD: Editorial is out

Hello everyone!

You might have noticed a new link in the main menu (top) already. Here you can see top-10 most interesting/discussed blog entries in recent time.

Here is some info on how we decide which posts to show on that page. First, we filter only those post which have some activity (comments/positive votes) in recent time, and each comment/vote has a weight that depends on its time. The newer the post/comment/vote is, the stronger effect it has on the post for getting into the top.

Thanks for you attention! :)

Hello, Codeforces. Below you can see the improvements in the system Polygon.

A lot of work has been done to simplify the preparation of school tasks, which use groups and points for tests. In the General Information tab, you can enable the points option for each test. This option is enabled points for the whole problem, that is, for tests from all testsets. Let me remind you that test groups can be enabled for each testset separately on the Tests tab.

Points for groups, points policies, dependencies

Points for the test, as well as groups, can be entered in the table with the list of tests, and also specify them when creating a new test. If the group for the test appears for the first time, it will be automatically added to the list of available groups. This list is presented in the table.

Hello!

Codeforces Round #486 (Div. 3) will start on June 1 (Friday) at 14:35 (UTC). It will be the third Div.3 round in the history of Codeforces. You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, 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. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

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 participants of the third division, you must:

• take part in at least two 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 my work. Thanks to Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for testing the round.

UPD: I also would like to thank step_by_step and eddy1021 for testing the round and help with it preparation!

UPD2: You will be given 6 problems and 2 hours to solve them.

UPD3: Editorial is published. Thanks to Mikhail PikMike Piklyaev for the help with translation.

UPD4:

Congratulations to the winners (official results):

Congratulations to the best hackers:

530 successful hacks and 401 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

I hope that you will like the problems. If the problems in this round are too easy or too hard, then we will adjust the difficulties in the next Div. 3 rounds.

Good luck!