The Codeforces Marathon Round 1 is over (results comment). As the final solutions are being tested, I think many participants will want to share ideas and learn alternative approaches. I'll start with the ideas I tried myself, both successful and not; as I've seen in the submissions, the contestants have more ideas, but I hope they will share themselves. For each of the solutions below, the numbers in square brackets are minimum, mean and maximum score when running on 1000 tests locally. I have to note in advance that the constants and technicalities in the solutions are not considered optimal: the score just shows approximate relation between ideas and may often be improved a bit.

Hello!

Let us remind you that Russian Code Cup 2016 Elimination Round will take place on June 19, 2016 at 14-00 Moscow time. Top 200 from each qualification round can take part in Elimination round, 200 best coders in Elimination round will get branded championship t-shirt, and top 50 will advance to the Final Round that will take place in September. There are money prizes to grab in the Final Round.

Good luck everyone and see you at http://russiancodecup.ru !

There has been talk about this already, but in case anyone missed it:

The 2016 edition of Internet Problem Solving Contest is going to take place today (starting time).

It's a 5-hour contest for teams of up to 3 people, but there's also an individual division, so feel free to participate even if you can't find yourself a team at this point.

There's going to be an ACM-like number of problems (12+), ranging from classic algorithmic problems to quite unusual ones. Most problems have an easy subproblem worth 1 point and a hard one worth 2 points (think CodeJam); ties are broken using ACM rules (sum of times).

The practice session is over. The contest is over!

Read the rules or my previous blogposts about this for more info.

Belated, yet necessary warning!

Since this is a 5-hour contest where you can execute codes locally, some inputs will be YUGE (gigabytes). Accordingly, they will have fairly high system requirements. Get a good computer. While the official solutions quite comfortably run on my mediocre laptop, if you write something too inefficient, you can encounter a nasty surprise, e.g. frozen system. It happened to me last year.

If an input is big, you won't have to download it; instead, there will be a generator (typically a Python script, meaning they aren't very fast). It's usually a good idea to run all generators as early as possible — as long as it doesn't slow down your computer too much, you can avoid a situation where you can't submit a problem because the contest ended before your generator.

Actually, you should just try to read as many problems as possible and determine your strategy after you can guess your chances well enough.

Some quick stats

11145 submissions
5370 successful submissions (48% success rate)
797 active teams out of 1376 (58% did not give up before even trying)
773 teams with positive score (97% of active teams)
12/13 problems solved by someone
maximum number of fully solved problems: 10/13
lowest non-zero success rate: D (D2: 20%)
highest success rate: C,F (C2,F2: 85%)

highest success rate (easy subproblems): G1 (85%)
lowest success rate (easy subproblems): J1,M1 (25%)

hard problems (<50 teams solved) sorted by difficulty:
E: 0/13
M: 2/10
J: 4/17
H: 11/17
B: 11/18
L: 16/46
K: 40/107

Hi everyone!

Codeforces Round #358 (Div. 2) will take place today on the 17th of June at 19:35 MSK.

I am the author of all the problems, and this is my first round on Codeforces. I hope you will enjoy it.

I'd like to thank Gleb GlebsHP Evstropov and Dan danilka.pro Sagunov for helping me in preparing problems, Mike MikeMirzayanov Mirzayanov for the great Codeforces and Polygon platforms.

There will be five problems and two hours for solving them. The scoring distribution will be announced later.

UPD

Scoring: 500-1000-1500-2000-3000

UPD

Editoral

UPD

Congratulations to winners!

Div.2:

1. Subway_Sandwich

2. mcdonalds

3. KentuckyFriedChicken

4. zijue

5. dacaiji

Div.1:

1. MrDindows

2. Um_nik

3. anta

4. uwi

5. Shik

The language of the round is Kotlin. Kotlin is a statically-typed programming language that runs on the Java Virtual Machine and also can be compiled to JavaScript source code. Its primary development is from a team of JetBrains programmers based in Saint Petersburg, Russia (the name comes from the Kotlin Island, near St. Petersburg).

Here is an example of the simplest program on Kotlin to print sum of two numbers:

fun main(args: Array<String>) {
    val (x, y) = readLine()!!.split(' ').map(String::toInt)
    println(x + y)
}

Here are some links to help you with Kotlin:

• https://en.wikipedia.org/wiki/Kotlin_(programming_language)
• https://kotlinlang.org/docs/reference/
• http://try.kotlinlang.org/ — be careful: reading from the console in the web-IDE is not allowed
• and Google!

You can download standalone compiler (version 1.0.1) by the link http://s.codeforces.com/files/kotlin-compiler-1.0.1.zip Also you need JRE (virtual Java machine), you can find it by the link http://www.oracle.com/technetwork/java/javase/downloads/jre8-downloads-2133155.html

The password from the archives with IDEA (IDE supporting Kotlin out of the box): c8bf9dd9b91ad9ff Links to IDEA are below or you can download it from the official website

Good luck!

====

UPD: You can predownload development pack (sorry, 300MB). In fact, you can take part without it — the Custom Invocation tab will be available during the contest. Also we will publish more compact tools 30 minutes before the start.

All archives are encrypted. The password will be announced 30 minutes before the contest.

========

Surprise Language Round #8 will start on June 16, 16:00 (UTC). It will be unusual entertaining contest. Solutions on the only programming language will be allowed.

Thus, it is expected that during the round, participants can get acquainted with the language and solve a few simple problems. The language will be announced 30 minutes before the start of the round. At the same time (or earlier but encrypted archives) we will publish the archives with the tools to write programs in this language.

I am pleased to announce that the top 20 participants will receive an exclusive t-shirt, and another 10 random participants among those who solved at least three problems will receive an exclusive t-shirt too.

The rules of the contest are as follows:

• The contest is unrated for everybody.
• The round uses ACM ICPC rules: the standing is defined by the number of solved problems, ties are resolved based on penalty time. Initially the penalty is 0, and for each solved problem it is increased by submission time (since the start of the contest) + 20 minutes for each failed submission. The solution is considered to be correct if it passes all tests from a predefined test set; you know whether the solution is right immediately after sending it. There are no hacks.
• The round will have 8-10 problems, sorted by estimated complexity, and you have 2 hours to solve it.
• Solutions are accepted only in one language, which will be announced in 30 minutes before the contest.
• Please reread this post at the beginning of the contest: we will announce the language and add instructions to install the compiler (the contest interface will provide an option to run your solutions online as well) and links to useful manuals. Other than that, learning the language is up to the competitor. You can use any resources to solve the problems (as long as you remember that this is an individual competition); you don't have to limit yourself to the manuals provided in the post.

Good luck!

Hi everyone!

Codeforces Round #357 (Div. 2) will take place today on the 14th of June at 19:35 MSK.

I am the author of all the problems, and this is my first round on Codeforces. I hope you will enjoy it.

I'd like to thank Gleb GlebsHP Evstropov and Dan danilka.pro Sagunov for helping me in preparing problems, Mike MikeMirzayanov Mirzayanov for the great Codeforces and Polygon platforms, and also Demid BLIZZARD Kucherenko for writing alternative solutions.

There will be five problems and two hours for solving them. The scoring distribution will be announced later.

UPD

Scoring: 500-1000-1500-2000-2500

UPD

Congratulations to winners!

Div. 2

1. pozhaluista
2. Bedge
3. jerjerisfat
4. Huyum_nik
5. OnlyYuju

Div. 1

1. uwi
2. anta
3. kmjp
4. ngfam_kongu
5. BigBag

UPD

Editorial

Hello, Codeforces!

Educational Codeforces Round 13 will take place on 13 June 2016 at 19:00 MSK for the first and the second divisions. Almost two months passed from the previous round. That is due the next reasons: 1) I coordinated regular CF-round at the end of April; 2) about whole CP community were busy with preparing and competing in ACM ICPC WF in May; 3) at the beginning of this month I start to work at AimTech (I hope that I'll have enough time to continue prepare ERs).

<It's need to read at least once maybe you'll find something interesting>

The round will be unrated for all users and it will be held with extented ACM ICPC rules. You will have two hours to solve six problems. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

If you have ideas for some problems or maybe already prepared problems that you can't use in rounds or official competitions, you can write to me.

It seems that it is harder to invent interesting simple problems (like A and B) than difficult ones. So don't be afraid to suggest interesting simple or very simple tasks (of course the difficult tasks are also needed). Please send only the problems for which you know the solution with clear statement (the story is not required). And also please add one or two samples to make the problem statement more clear.

</It's need to read at least once maybe you'll find something interesting>

The problemset was suggested by Codeforces users. The problem А was suggested by user Abdrakhman Ismail bash. The problem B was suggested by Arthur Jaworski KingArthur. The problem C was suggested by Sheikh Monir skmonir. The problem D was suggested by Zi Song Yeoh zscoder (there are a lot of unused his problems). The problem E was suggested and prepared by Alexey Dergunov dalex. The simpler version of the problem F was suggested by AmirMohammad Dehghan PrinceOfPersia.

Thanks a lot to them and all others who are sending the problems! The number of unused problems are increasing. If I didn't miss anything I already replied to all who sent me the problems at least 5-6 days ago. Please be patient if your problem was not used a long while.

As I said the problem E is prepared by Alexey Dergunov dalex. All other problems was prepared by me (Edvard Davtyan). Thanks to Tatiana Semyonova Tatiana_S for checking the English statements. The problems was tested by users suggested them, respectively: Abdrakhman Ismail bash, Arthur Jaworski KingArthur, Sheikh Monir skmonir, Zi Song Yeoh zscoder, Alexey Dergunov dalex and AmirMohammad Dehghan PrinceOfPersia. Thanks a lot to all of them!

I hope you will enjoy the problems! Previous time the problems were too hard. I've tried to fix that. The problems should be simpler than usual.

Good luck and have fun!

UPD: The round is finished. The editorial is published.

It's the first summer round :-)

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.