Hello, Codeforces! I'd like to invite you to Codeforces Round #289 (Div. 2). It'll be held on Saturday, January 31 at 15:00 MSK and as usual Div. 1 participants can take part out of competition.

This round will be carried out according to the ACM rules, which means that you get verdict of your solution on-line, and the duration time is 3 hours.

These differences in the rules are caused by the fact that this round is the second qualifying round for the WCC, which stands for Winter Computer Camp and can be also mentioned as ZKSH. Official school website — hhttp://it-edu.mipt.ru/en/zksh2015. There you can find the selection rules for WCC.

If you are a school student and you want to participate in the selection to WCC here are the steps:

1. Sign up for the school at http://goo.gl/kz2qSf, if it was not done earlier.
2. Create a free account at codeforces.com, if it was not done earlier.
3. Sign up for the round on the link [to be announced]. You should put a tick in the box "Do you want to participate in the selection to WCC?", and provide your last name, first name and email, which you entered for registration in the first step.

If you have any questions feel free to write to the address of the organizing committee: zksh-team@phystech.edu.

The authors of the contest (WCC technical committee) are really grateful to Max Akhmedov (Zlobober) for the help with preparation of this round, Maria Belova (Delinur) for translation of statements and Mike Mirzayanov (MikeMirzayanov) for contribution to the development of programming by creating systems Codeforces and Polygon.

Hello, Codeforces!

I'd like to invite you to Codeforces Round #288 (Div. 2). It'll be held on Tuesday, January 27 at 19:30 MSK and as usual Div. 1 participants can join out of competition.

Great thanks to Maxim Akhmedov (Zlobober) for helping me preparing the contest, to Maria Belova (Delinur) for translating the statements into Russian, to Mike Mirzayanov (MikeMirzayanov) for the great Polygon platform and ideas of some problems and to my dear teammates Arthur Svechnikov (ikar) and Ilya Los (IlyaLos) for writing solutions.

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

UPD Score system is standart 500-1000-1500-2000-2500.

UPD2 Competition completed! Thank you all!

UPD3 You can find editorial here.

UPD4 Congratulations to the winners!

1. topcoder.2015
2. KimJongUn_JBYongDongJI
3. atatomir
4. pankaj_gudlani
5. egor_bb

A reminder that today at 21:00 GMT the second round of Facebook Hacker Cup 2015 is taking place. After first round last weekend 732 contestants are continuing the battle. Top 100 from the second round advance to the third, while top 550 receive T-shirts. The round will be 3 hours in length. For contestants the tasks will be available here, while the standings — here.

UPD: Round is over, provisional results have been published. Cutoffs:

• Advancement to Round 3: 55 points (A+B+C) with time ≤ 2:21:53
• Facebook Hacker Cup 2015 T-Shirt: 10 points (А) with time ≤ 30:23

Hello Codeforces!

I'd like to invite you to Codeforces Round #287 (Div. 2). It'll be held on Friday, January 23rd at 19:00 MSK. and as usual Div. 1 participants can join out of competition.

This is my first round so wish me luck! :)

Great thanks to Maxim Akhmedov (Zlobober) for helping me preparing the contest, Alex Fetisov (AlexFetisov) for testing and giving useful tips regarding statements, Maria Belova (Delinur) for translating the statements into Russian and Mike Mirzayanov (MikeMirzayanov) for the great Polygon platform.

The scoring distribution will be announced later.

Good luck everyone and I hope you'll find the problems interesting.

UPD #1 Score distribution will be standard 500-1000-1500-2000-2500.

UPD #2 Contest finished, hope you enjoyed the problems. :)

UPD #3 System testing finished.

Winner of the contest is going to be disqualified due to "Do not use harsh, rude or misleading handle." part of Codeforces rules.

So congratulations to the winners:

chickennethsnow

donghao3

mikeyue_tc

Black.Salami

KilluaZoldyck

UPD #4 You can find the editorial here.

I'm planning to make a scoreboard for the ACM ICPC World Finals 2015, the scoreboard will contain the TopCoder and Codeforces handles for the contestants. It will be similar to this one (but with some more improvements).

Please post the Codeforces handles for the qualified teams here. I'll keep updating this post once I get any new information.

Any suggestions for the scoreboard are welcome for sure.

I'll add all the handles I get in the following table:

Hi Codeforces!

My name is Maxim Gusarov and I joined the Codeforces developer team in September and am recently working with Vitaly kuviman Kudasov on improving the Polygon system.

Today I would like to introduce you to the new potential of the system where all problems for the Codeforces rounds and many other programming contests are prepared.

Update 1

As a user logs into the system, she can now use either the login or the email given at the registration. You can also attach the session to the IP address to enhance security.

Update 2

Any user who has the access to edit a problem can become its supervisor. The supervisor will always get email notifications about the changes committed to the problem even if they were committed as “Minor changes”. What you need to do is to open the problem, go to the “Manage Access” tab and set “Supervisor” after your name.

This option can be used for the problem author or the contest coordinator not to miss a single change.

Hello, Codeforces!

In late December and early January, I wrote a proof-of-concept of separate service in C ++, to take out heavy data from the Codeforces Java-code to C++. Long time I have not written in C ++, experienced a funny sense of immersion into another world.

I was surprised to find the lack of open-addressing hashmap in the C++ standard library, and indeed in the boost, and in other popular libraries. It is strange somehow, because often open addressing should be better than separate chaining both in time and memory. And since I intend to keep small objects, then sure.

I quickly sketched a prototype that actually shows that open addressing in 2-3 times faster than the standard std::unordered_map. Here's the output of the benchmark on my laptop:

std :: map takes 15779 ms
std :: unordered_map takes 4698 ms
oaht :: hash_map takes 1473 ms

I think that there is no good implementation of such container in stl-style with the support of C++11 (move semantics). Maybe someone will show, but I have not found.

Here is my prototype on github: https://github.com/MikeMirzayanov/open_addressing_hash_table Unfortunately, I'm not cool C ++ expert, and I have no time to implement.

On the other hand, on Codeforces where were many C ++- discussions, and seems there many users who understand modern C ++. Also algorithms are water and air of Codeforces!

Hello Codeforces!

evima, yosupo and I would like you to participate in Codeforces Round #286. It will be held on Sunday, January 18th at 16:00 MSK. Please note that this round starts on unusual time.

Great thanks to Zlobober who helped us prepare this round, Delinur who translated statements into Russian and MikeMirzayanov who created Codeforces and polygon.

This is the 3rd time(following #162 and #263) for me, and the 1st time for evima and yosupo to prepare a Codeforces Round.

Scores of the problems will be

500-1000-1750-1750-2500 for Div.1, and

500-1000-1500-2000-2750 for Div.2.

In this round, you'll help a man named Mr. Kitayuta. I hope he will participate :)

The system tests are now over! The top-5 are as follows:

Div.1:

1.ilyakor

2.kcm1700

3.LayCurse

4.RomaWhite

5.TankEngineer

Div.2:

1.HYEA

2.cpcpc

3.zgzjsxshycxksxhsh

4.Ronnie007

5.sha384

Also, special congrats on Petr, who solved problem E in Div.1, which anyone else could not solve.

Here are the editorials