Hi everybody!

I'm glad to invite you to the Yandex Algorithm Round 2 that will happen tomorrow at 21:00 Moscow Time. This round is prepared by me with a great help of GlebsHP. I want to say thanks to Chmel_Tolstiy, snarknews and Gassa for their support during the preparation and to all of the Yandex developers that tested this round.

Good luck and have fun!

Link to the contest will be posted here as soon as I manage to find it by myself :)

UPD: the link to the contest is located here: https://contest.yandex.com/algorithm2016/contest/2540/enter/

UPD2: Thanks everybody for the participation, I hope you enjoyed the round! Results will be available shortly. I'd like to publish an editorial, but it fails to compile on Codeforces and I'm trying to fix this issue.

UPD3: Congratulations to winners:

1. jqdai0815
2. eatmore
3. rng_58
4. jcvb
5. KAN

The preliminary pdf-version of an editorial is posted: http://codeforces.com/blog/entry/45354. Continuing the nice tradition of providing an editorial with questions related to the problems, I invite you to think about them/

Hello Codeforces.

The CF Round #356 will happen on 8-th June (exact time). You will get five problems to solve in two hours. The round is rated.

I encourage you to read other problems if you don't like or can't solve something. The scoring distribution will be announced.

MikeMirzayanov and GlebsHP make the round possible. Also, thanks for Radewoosh, kostka, johnasselta, AlexFetisov and (more to be added?) for their amazing help. And I want to thank my girlfriend because there would be no Limak without her.

It's my first standard round. Still, you should get nice interesting problems. You will meet Limak, who is usually a little polar bear. Here he is, preparing one of problems.

I wish you great fun and no frustrating bugs.

EDIT — It's recommended for both divisions to read the Interactive Problems Guide before the round.

EDIT2, SCORING

div2: 500-1000-1750-2250-2750
div1: 750-1250-1500-2000-2500

EDIT3

The editorial with codes is ready.

WINNERS, congratulations!

1. Petr
2. ainta
3. halyavin
4. jcvb
5. brandnewnode

and Division 2:

1. Y_UME
2. kaq
3. BehtarinFake
4. Zoli9
5. Jeannette

Thank you all for participation and see you next time. And regards from Limak, a bear.

Sometimes you can meet interactive problems on programming contests (including Codeforces).

In problems of this type, the input data given to your program may be not predetermined but is built specifically for your solution. Jury writes a special program — interactor, such that its output is tranferred to the input of your solution, and the output of your program is sent to interactor’s input. In the other words, your solution and the interactor exchange the data and my decide what to print based on the "history of communication".

When you write the solution for the interactive problem it is important to keep in mind that if you output some data it is possible that this data is first placed to some internal buffer and may be not directly transferred to the interactor. In order to avoid such situation you have to use special flush operation each time you output some data.

Hi, all!

The last possibility to get to the Elimination Round of Russian Code Cup this year is the Third Qualification Round, that will take place on Sunday, June 5, 16:00. Everyone who has not yet qualified is welcome to participate. Good luck, and see you at Russian Code Cup 2016!

Today, June 2, 2016 year, there was a technical failure, which I will remember for a long time. Several factors led to a serious malfunction of the Polygon system.

The fact that in the middle of May Polygon was transferred to servers located in Mail.Ru data centers. To transfer with almost no downtime (Polygon has a lot of data, about a terabyte) lsyncd utility has been used, which quickly pushed the file changes from the old server to the new one.

Today there was a reboot of the old server, which forced the unplanned start of lsyncd daemon. As a result it did the synchronization of data from the old server to the new again. So, data stored in the file system have been rolled back to the transfer time (May 13). The most unlucky fast that, unlike the old server where the backups system was set up well and reliable, on the new server, I quickly managed to set up only replication using the same lsyncd, which does not help in the incident of files deletion (as it forces the removals on the replica). Obviously, RAID-1 disks didn't save the data.

As a result, all file changes in the Polygon system made in three-week period were lost. Some information (statements, etc) is stored in the database, so accessible.

This night I urgently implemented the special link "Scraps" to download the archive with the available data. If a problem has been used in the Codeforces infrastructure, the packages remain in its cache of the judging system, they are available in archive.

I feel lousy realizing that my lack of attention to detail has led to such consequences. I distinctly remember the black day of Codeforces — and as a result many things have been much revised (everywhere mirrored disk arrays, replicas and backups). Unfortunately, this time after moving to new hardware I did not return all scripts and here is the result. Problem writers please accept my deepest apologies for my mistake.

Greetings to the Codeforces community!

Regular Codeforces round #355 for participants from the second division will take place on 1 June, 19:35 MSK. Participants from the first division are able to participate out of the contest.

It is my third round on Codeforces. Hope you will enjoy this round.

I want to thank Gleb Evstropov (GlebsHP) for help with preparation of this round and Mike Mirzayanov (MikeMirzayanov) for great Codeforces and Polygon systems.

Participants will be given five problems and two hours to solve these problems.

UPD Score distribution: 500-1000-1500-2250-2250

UPD Editorial is here

UPD Congratulations to the winners!

Div. 2

1. fake_fake

2. __Wind

3. Mamedov

4. dianaasau

5. Sorry_Daikon

Div. 1

1. Um_nik

2. TimonKnigge

3. vintage_Vlad_Makeev

4. anta

5. kmjp

Hi all!

The second qualification round of Russian Code Cup 2016 will take place on Sunday, May 29, 2016, at 12-00! We invite everyone who has not qualified yet to take part. Those who would not qualify in the second round are invited to take part in the third round on June 5. Good luck to everyone and see you at the round, don't forget to register for the championship at http://russiancodecup.ru if you haven't done so already.

Hello, Codeforces!

I'd like to invite you to Codeforces Round #354 (Div. 2). It'll be held on Wednesday, May 25 at 18:05 MSK (Moscow time) and Div. 1 participants can join out of competition. As usual round starts in the unusual time!!!

Me an Grigory AGrigorii Akhremenko prepared the tasks for this Round. It is the debut for Grigory as the problemsetter.

Great thanks to Gleb GlebsHP Evstropov for helping us preparing the contest, to Mike MikeMirzayanov Mirzayanov for the great Polygon platform and for Ilya IlyaLos Los and for Artur ikar Svechnikov for writing solutions.

The scoring distribution will be announced later. Good luck everyone!

UPD Score distribution 500-1000-1500-2250-2250

UPD2 Editorial

UPD3 Congratulations to the winners

1. Thomas66

2. super_wormy

3. Valkata.a.k.a.TheHacker

4. tcchung

5. Krktv

UPD4 See you soon!=)

Yesterday ACM ICPC World Finals finished. We congratulate all winners, medalists and special prize winners!

We want to remind you that tomorrow, May 21, at 00:00 (UTC+3) the qualification round of Yandex.Algorithm will start. For participation in qualifications you should register and start a virtual contest at any time prior to May 23 (UTC+3).

As usual 6 problems of varying difficulty will be provided at Yandex.Algorithm rounds. In order to qualify for the elimination stage rounds and compete for a trip to the finals in Minsk and other prizes you should solve at least one problem.

Also Yandex.Algorithm offers students to participate in the internship track. For more information see the rules of the championship.

Good luck! See you at Yandex.Algorithm!

P.S. The qualification round has started. Problems prepared by Romka, Ixanezis and Chmel_Tolstiy.

EDIT. Analysis has been posted.