By map2 days ago, translation, In English,

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 — h 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, if it was not done earlier.
  2. Create a free account at, 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:

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.

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By fcspartakm4 days ago, translation, In English,

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

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By eduardische7 days ago, translation, In English,

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

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By AmrMahmoud9 days ago, In English,

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:






UPD #4 You can find the editorial here.

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By ahmed_aly7 weeks ago, In English,

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:

Country University Contestant 1 Contestant 2 Contestant 3
1 Argentina Facultad de Ciencias Exactas-Universidad Nacional de Rosario karupayun mariano22 martinv
2 Argentina Universidad de Buenos Aires — FCEN melsclar tavo92 zylber
3 Bangladesh Jahangirnagar University bhadra Flaminrage nfssdq
4 Bangladesh Shahjalal University of Science and Technology Corei13 J-C maruf_0011
5 Belarus Belarus State University of Informatics and Radioelectronics asmisha dberezhnov tanas
6 Belarus Belarusian State Economic University hired777 Liaksiejka sas4eka
7 Belarus Belarusian State University kolesov93 nekrald qwaker.00
8 Bolivia Universidad Privada de Santa Cruz de la Sierra Ademord alexpizarroj josemanuel101
9 Brazil Universidade Federal de Campina Grande deMatos manoel rafaelclp
10 Brazil Universidade de São Paulo antonio_junior marcoskwkm StefanoT
11 Canada University of Waterloo dojiboy9 goffrie Radiosity
12 China Beihang University InheritG InheritO sd0061
13 China Beijing Institute of Technology nono s0en1it YYone
14 China Beijing Jiaotong University kybconnor Lquartz Ryan_MuQ
15 China Huazhong University of Science and Technology Hellis hust_laz once8203
16 China Shanghai Jiao Tong University AngryBacon rowdark yefllower
17 China Shanghai University kuangbin shu_mj zhangxiaohao
18 China Tsinghua University ACMonster Eternal_Answer Leo_Yu
19 China University of Electronic Science and Technology of China hlwt qph-Jeremy xiaoke
20 China University of Science and Technology of China mynameisverylong ufo172849z wilsonlym
21 China Zhejiang University chnluyi Dark_sun zimpha
22 Colombia Universidad Nacional de Colombia — Bogotá DiegoCR lemur niquefa_diego
23 Croatia University of Zagreb gustav ikatanic stjepan
24 Cuba University of Havana jcg MarX otero1991
25 Czech Republic Charles University in Prague fhlasek mirecek3
26 Egypt Arab Academy for Science and Technology (Alexandria) adelnobel Haytham.Breaka MoustafaMaher
27 Egypt Cairo University — Faculty of Computers and Information ahmedhamed mc_mosa moh.amr
28 Egypt Faculty of Computer and Information Sciences, Ain Shams University ahmed0mohsen ahmedameen zetamoo
29 Egypt Faculty of Engineering, Ain Shams University ahmed_fathy_aly alwahsh RedNextYears
30 Egypt German University in Cairo .Khaled. Mohamed.Bassem TheSavageKoder
31 Egypt The American University in Cairo ghooo Hosam_Samy islamdiaa
32 Georgia Free University of Tbilisi guliashvili svanidz1 TMandzu
33 India Indian Institute of Technology, Roorkee adurysk amankedia1994 straw-hat
34 India International Institute of Information Technology, Hyderabad karanaggarwal pulkitg10 viv001
35 Indonesia University of Indonesia athin Gyosh sokokaleb
36 Iran Shahid Beheshti University farzad.shbfn m.haghpanah
37 Iran Sharif University of Technology haas LGM mR.ilchi
38 Japan University of Tokyo rng_58 semiexp wrong
39 Kazakhstan Nazarbayev University ADJA An4ik.D kt-9
40 Mexico Escuela Superior De Computo Instituto Politecnico Nacional ChOmPs Garo9521
41 Peru Universidad Católica San Pablo alculquicondor darkloz jainor
42 Poland Jagiellonian University in Krakow guspiel m.sewcio piob
43 Poland University of Warsaw Errichto johnasselta mareksom
44 Poland University of Wroclaw bardek matix2267 Solaris
45 Romania University of Bucharest a_h1926 freak93
46 Russia Moscow Institute of Physics & Technology kuzmichev_dima pershik ssmike
47 Russia Moscow State University _meshanya_ GlebsHP TeaPot
48 Russia Saratov State University fcspartakm IlyaLos ikar
49 Russia St. Petersburg Academic University evgentu geka666 nk.karpov
50 Russia St. Petersburg National Research University of IT, Mechanics and Optics qwerty787788 tourist VArtem
51 Russia St. Petersburg State University Copymaster KapJI Seemann
52 Singapore Nanyang Technological University con_nha_ngheo sillyboy tuananh93
53 Singapore National University of Singapore darknsux jonathanirvings nathanajah
54 South Korea Korea Advanced Institute of Science and Technology etaehyun4 mjy0503 protos37
55 South Korea Korea University cauchy_function Myungwoo wclee2265
56 South Korea Seoul National University lemonsqueeze pjsdream zlzmsrhak
57 Spain Universitat Politècnica de Catalunya angargo drbioi FerranAlet
58 Sweden KTH — Royal Institute of Technology Gullesnuffs jsannemo simonlindholm
59 Syria Tishreen University Blackjaguar97 majd.gda1 samiemad
60 Taiwan National Taiwan University fenzhang lnsuyn Nekosyndrome
61 Ukraine Lviv National University I_love_Tanya_Romanova RomaWhite witua
62 Ukraine Odessa National Mechnikov University Monyura Sfairat Sklyack
63 Ukraine Taras Shevchenko Kiev National University Fdg Furko M0sTik
64 United States Cornell University edufgf marinheiro victoreis1
65 United States University of California Los Angeles gaoxin lcch MatRush
66 United States University of Central Florida edorundo jcomputer000 tylerbrazill
67 United States University of Southern California cgy4ever ghostgold innovator
68 United States University of Minnesota — Twin Cities GoldenGopher HidenoriS nil_mo
69 Venezuela Universidad Simón Bolívar avatar_tp josegpg WRBH
70 Vietnam Vietnam National University Aquacloud net12k44 ntit_co1

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By Avalanche5 weeks ago, translation, In English,

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.

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By MikeMirzayanov12 days ago, translation, In English,

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: 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!

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By hogloid13 days ago, In English,

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:













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

Here are the editorials

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