By Arpa, history, 9 days ago, In English,


I'm honored to invite you to Codeforces Round #383, it will be held on 6nd December 14:35 UTC. There will be 5 problems for each division as usual. The contest was prepared by AmirReza Arpa PoorAkhavan and Mehrdad _-_Sa1378_-_ Saberi. It's our first official contest at CodeForces.

The contest stories will be about Arpa and Mehrdad and some events happen with them in Arpa's land, in addition you will get some information about Arpa's land and girls living there (Owf (t = 1)).

I'd like to thank myself (:P) and Mehrdad at first, then Nikolay KAN Kalinin for helping me in preparing problems and Mike MikeMirzayanov Mirzayanov for the great Codeforces and Polygon platforms.

The scoring distribution will be announced later.

Answer for one of your common questions : -Yes, It is rated.

UPD. GL & HF. Hope you came up with Dokhtar-kosh solutions for our Dokhtar-kosh problems.

Urgent information from MikeMirzayanov: due to hardware issues, the round is moved to Tuesday 6th December, 14:35 UTC. We are very sorry this happened. More information is available in this post.

UPD. Scoring distribution: Div.1 : 500-1000-1250-2000-2500, Div.2 : 500-1000-1500-2000-2250.

UPD. Contest is over, hope you have been Joon-Joon of the round :P

Congratulations to winners:


1 . TooDifficuIt

2 . mnbvmar

3 . data_h and nuip (WoW :O)

5 . Phronesis

Sepcial congratulations to anta who solved Div.1 E.


1 . gilcu3

2 . toHisDream

3 . FaRZaM_Z

4 . 768092

5 . orz_liuwei

Editorial is ready.

Read more »

  • Vote: I like it  
  • +435
  • Vote: I do not like it  

By niyaznigmatul, 7 days ago, translation, In English,

Hello, Codeforces.

This weekend ITMO University in St. Petersburg with Barnaul, Almaty and Tbilisi will host ACM ICPC Northeastern European Regional Contest. text

We have 266 teams (thanks to MikeMirzayanov and snarknews for the link) competing for the chance to go to the ACM ICPC World Finals 2017 which is going to take place in South Dakota, USA.

In ITMO University site 106 teams will compete, including ACM ICPC 2016 World Champions and the team that is leading Opencup ranklist.

We have an Instagram account, we will post there some pictures from contest halls and other weekend activities.

If you are not competing in NEERC, you can try to solve the same problems in mirror. It will take place at 8 AM UTC, December, 4.

Contest scoreboard.

Some NEERC teams with their Codeforces ratings
Team name Team member 1 Team member 2 Team member 3 Total rating
SPbSU Base aid (2765) ershov.stanislav (2739) -XraY- (2551) 8055
MIPT Jinotega zemen (2741) ifsmirnov (2721) Arterm (2506) 7968
ITMO University 1 izban (2762) enot.1.10 (2550) Belonogov (2545) 7857
Perm SU Indigenous I_love_Tanya_Romanova (2650) mmaxio (2576) KuchumovIlya (2411) 7637
Saratov SU 1 HellKitsune (2537) dans (2485) IlyaLos (2349) 7371
ITMO University 2 BudAlNik (2450) YakutovDmitriy (2422) SpyCheese (2413) 7285
Belarusian SUIR netman (2571) andrew.volchek (2318) teleport (2247) 7136
SPbSU 3 Kaban-5 (2474) pavel.savchenkov (2431) tunyash (2226) 7131
Ural FU Charmander Tinsane (2438) kb. (2363) KungA (2262) 7063

Good luck to all participants

Read more »

  • Vote: I like it  
  • +278
  • Vote: I do not like it  

By gKseni, 2 weeks ago, translation, In English,

University Innopolis is organizing and holding Innopolis Open, an Olympiad in Informatics for secondary school students (until 19 y.o.). The Olympiad consists of two rounds — online contest and the on-site competition (held at Innopolis, Russia).

Winners of the first round will be invited to Innopolis to take part in the on-site competition. During the Olympiad, all participants will be offered a free of charge accommodation, meals and transfer from Kazan to Innopolis and back.

Winners of the second (on-site) round will receive awards and can be enrolled in Innopolis University without any admission tests.

  • The first (online contest) round will start on December 18 at 10.00 a.m. (UTC +3).

  • The second (on-site) round will take place on February 25-26 in Innopolis city, Russia.

Registration is open until December 15, 2016. Participation is free of charge.

Please follow the link to register and find detailed information.

Read more »

  • Vote: I like it  
  • +58
  • Vote: I do not like it  

By MikeMirzayanov, 11 days ago, translation, In English,

Good afternoon!

I've decided to share my thoughts on the round 382.

Of course, it turned upset not only to me, but also to the round coordinator GlebsHP.

In this round the main negative feedback were caused by two problems: 735D - Taxes and 735C - Tennis Championship.

Regarding 735D - Taxes. I do not share the criticism to this problem. In fact, to solve it would be nice to be familiar with Goldbach's Conjecture and better with Prime Number Theorem. These facts are medium-popular in the world of programming contests. Familiarity with them is useful, gives useful insight into primes. It is important: in this problem it was necessary to perform a simple, but nevertheless, additional step to find solution. It seems to me that it's okay to use problems that have a reduction to some popular and semi-popular topics. Otherwise, it is thrown away a huge number problems.

As a summary for this problem. I agree that the problem 735D - Taxes is not an example of the best problem. But it has a right to exist as one of the problems in a round. It can not take a role of any argument in favor of unrated round. I personally, would not include it in my contest. But the fact of the use of the Goldbach's conjecture (and more prime number theorem) is not a reason for me to convict and forbid a problem.

The situation with the problem 735C - Tennis Championship is much more complicated. It is necessary not to mix the two fundamentally different reasons for occurrence of same problems:

  • Problems can be matched randomly, inadvertently. Of course, the coordinator and testers always have a critical look on the problem. At the stage of the contest preparation they immediately react if a problem is familiar to somebody. It is important to understand, that huge number of problems have been invented over the years of existence of sports programming. It is physically impossible to be familiar even with a large part of them. No matter how experienced the jury, sometimes, coincidences happen. Note that if the round is not a stage of a championship and its results do not affect prizes the main reasons for participation in it should be self-development and a desire to get a fan from the competition. None of these goals encourage search in Google.

  • Deliberate coincidence or reuse of problems, it is a different story. And here it is what happened. This situation is totally unacceptable (educational rounds do not count), it is necessary to fight with it and to respond rapidly to incidents.

As soon as I examined about the incident, immediately called by phone the writer and discussed (and denounced) the situation. I explained the inadmissibility of such cases and their implications. I think Albert made the correct conclusions and will be accurate in future. Unfortunately, I was informed about incident only after the ratings been updated.

Taking into account large number of participants who didn't notice the issue, who solved problems completely independently, who were happy of upset by their rating changes, shared their results in social networks it does not seem respectful to do to them unrated. I share the view that it would be better not to be so, but history has already taken place. Note that if I learned the situation during the round or immediately after, the outcome might be different. I think it's a good idea to report suspected cases through questions to give a chance the coordinator or me react quickly.

As a conclusion, I do not propose to raise the tragedy, coordinators do not despair. The writers, of course, need to understand the responsibility and importance of taking on the role. Thousands of participants come to solve your problems and, of course, expect something interesting and new.

I urge the community not to forget about respect for the work of authors: to prepare the contest is a big and difficult task. The author takes on a difficult role and if a round took place, so the hard way from the idea to the final implementation has done. Please, be grateful for it, say the authors, coordinators and testers, thank you!

Whatever effort the Codeforces team makes, we can not do rounds without the writers. Therefore, we look forward to your problems. Hope to see good and bright rounds here!

Thank you for attention,

Read more »

  • Vote: I like it  
  • +1301
  • Vote: I do not like it  

By albertg, 3 weeks ago, translation, In English,

Hi Codeforces community! I am glad to announce that at 27 November 16:35 (GMT time) will take place Codeforces Round #382 for participants of both divisions.

Author of this round is me (albertg). I am from Armenia and the only Armenian author of any Codeforces round yet. (Sorry Edvard). This round is my second round and I hope this is not the last one! :) it is the last one. As usual, I'm thankful to the coordinator of Codeforces Gleb Evstropov (GlebsHP) for helping to prepare this round and Mike Mirzayanov (MikeMirzayanov) for wonderful platforms Codeforces and Polygon. Also special thanks to Super_azbuka for an idea of a problem.

As usual, contestants will have 5 problems and 2 hours to solve the problems. In this round you should help Ostap Ibrahim Bender to reach Rio-de-Janeiro. Good luck and have fun!

UPD1: Scoring: div1 750-750-1500-2000-2500, div2 500-1000-1750-1750-2500.

UPD2: Editorial is posted.

UPD3: If somebody has question(s) about solutions of problems, please write me a personal message.

UPD4: Please read this.

UPD5: Editorial of problem div2E/div1C is posted.

Read more »

  • Vote: I like it  
  • +111
  • Vote: I do not like it  

By doreamon, history, 2 weeks ago, In English,

Sorry for my bad English >__<

There is a small contest called "Weekly Training Farm #14" hosted in one hour latter.

Weekly Training Farm Contest Series are hosted in Codeforces group tw-icpc-blog

These problems are mixed by old problems in many judge and some original problem.

You can see the last contest Weekly Training Farm #13 to understand the style of problems.

The Series contest is hosted in order to spread programming contest in Taiwan. But there are only little participants :(

As problem setters, I hope there will be more people can see these problems. So I post the blog to invite everyone. Thanks~

UPD: If you can read Chinese(Traditional), you can find editorial Here.

UPD 2: The English editorial is here.

Read more »

  • Vote: I like it  
  • +194
  • Vote: I do not like it  

By, history, 2 weeks ago, translation, In English,

Hi everyone!

Codeforces Round #381 will take place tomorrow on the 23rd of November at 19:35 MSK.

The problems were prepared by Alexander Alexandr_TS Tsaplin, Maxim HellKitsune Finutin and me. I hope you will enjoy it.

I'd like to thank Gleb GlebsHP Evstropov, Nikolay KAN Kalinin and Yevhen MrDindows Zadorozhnii 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.


Scoring for both divisions: 500-1000-1500-2000-2500


Congratulations for winners.

Div 1:

  1. TooDifficuIt

  2. FatalEagle

  3. izban

  4. LHiC

  5. Stonefeang

  6. Egor

Div 2:

  1. liumh8

  2. retired_coder

  3. fuboat

  4. Valerich

A special congratulations to Petr for being the only contestant to solve the problem D in div. 1.


The editoral in english will be published tomorrow, but you can read it now in russian


The editoral was added for the first five problems.


The editoral was added for the Div.1 D and Div1. E.

Read more »

  • Vote: I like it  
  • +234
  • Vote: I do not like it