Yandex.Algorithm Round 3 will start on June 13, 2016 on 07:00 (UTC).

This round follows TCM/Time rules and goes for 100 minutes.

Top 25 contestants by cumulative elimination stage results will advance to the final round.

Check out current scoreboard!

Best of luck! :)

Hi all!

I invite you to take part in Codeforces Marathon Round 1. It is an unrated contest in which the participants will have to solve one problem as best as they can. The problem is presumed not to have a fast full solution. A score is given for each individual test according to the quality of the answer found. The goal is to get the highest total score. The contest will go on for 10 days. The start time is June 12 at 12:00 MSK.

During the main phase of the contest, solutions will be checked on examples and preliminary tests. After the main phase is over, the final solution of each contestant will be checked on the final test set, and the total score for this test set will determine the final scoreboard. The 10 top scoring participants, as well as 10 random participants who achieve a good enough score, will get T-shirts. The contest is supported by Codeforces and the Community Of Master Programming at St. Petersburg State University.

This round is experimental: if something breaks, don't be upset, just write about it, and we will try to fix it.

See you in the contest!

Update 1 (12.06.2016)

You can take part in the contest as a team of two people! Both participants must not be registered as individual participants. If you are already registered but did not take any action in the contest, registration can be canceled at the respective page. Note: as the contest was initially planned for personal participation, if a team wins a T-shirt, it will get only one T-shirt.

Update 2 (19.06.2016)

There are a bit less than three days left till the end of the contest. Clarification: the 10 random T-shirts will be distributed among those who are not in the top 10, but get at least half of the possible score on the final tests (for 1000 tests, the boundary score is 500500).

To the best of my knowledge, Felix did not yet get to the very end of the exam in any of the preliminary tests. Who will help the robot? If you did not yet try, it is easy to start: in the development pack available on Github, there are example solutions in seven programming languages, and also tools to run a solution locally with the interactor.

I asked the Codeforces about recent progress. That's what they told me:

Polygon:

• true language autodetection (Polygon tries to compile a source using different dialects),

• you can upload multiple items simultaneously on the tabs Files and Solutions,

• feature to view stderr for invocations,

• Rejudge/Abort links inside invocation page,

In addition, the work on API continues.

Codeforces:

• preview comment when editing;

• filter by problems on hacks page;

• improved choice of t-shirt size;

• the ability to change the handle once in the first 7 days after a registration;

• improved performance of some API methods.

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.net/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