KAN's blog

By KAN, 5 weeks ago, translation, In English,

Hi all!

This weekend, at 16:05 UTC on November 12th, 2017 we will hold Codeforces Round 445. It is based on problems of Technocup 2018 Elimination Round 3 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2018 website and take part in the Elimination Round.

I want to thank MrKaStep, komendart, veschii_nevstrui, bixind, AndreySergunin and DPR-pavlin, who authored and prepared problems for Technocup, and lewin, who kindly suggested the last problem. I also want to thank zemen and AlexFetisov for testing the round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

UPD: We apologize that we run into technical issues during the round. The round will be unrated. I hope you liked the problems.

Anyway, congratulations to winners!

Технокубок 2018 - Отборочный Раунд 3

  1. potapov_al
  2. gainullin.ildar
  3. qoo2p5
  4. Vosatorp
  5. manoprenko

Codeforces Round #445 (Div. 1, based on Technocup 2018 Elimination Round 3)

  1. V--o_o--V
  2. Petr
  3. Um_nik
  4. SirShokoladina
  5. LHiC

Codeforces Round #445 (Div. 2, based on Technocup 2018 Elimination Round 3)

  1. mosthenio
  2. Ingugugus
  3. paulsohn
  4. xX_ucfNOTpt_Xx
  5. OmarYasser

Editorial is published.

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By KAN, 5 months ago, translation, In English,
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Thanks Arpa for this editorial!

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Thanks Arpa for this editorial!

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By KAN, 5 months ago, translation, In English,

The analysis is being updated.

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Thanks Arpa for the proofs!

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By KAN, 5 months ago, translation, In English,

Hi!

On Thursday, July 13, 2017, at 15:05 UTC Codeforces Round #424 will be held. Some of the problems will be from VK Cup 2017 Finals, some are prepared by Codeforces team to complete the problemset.

There will be six problems in the second division, five as usual in the first, three of them shared. The problems of this round are proposed, prepared and tested by: send_nodes, akvasha, ilya_the_lamer, fcspartakm, Perforator, MikeMirzayanov, PavelKunyavskiy, qwerty787788, Belonogov, izban, tourist, vepifanov, AlexFetisov, winger, Errichto, Gassa, naagi, ashmelev, Endagorion, ifsmirnov, Arterm and me. Huge thanks to all who helped with the preparation!

There will be prizes from VK social network in this round as well! Namely, among participants solved five or more problems in second division, or two or more problems in first division, five are to be selected randomly. They will receive championship souvenirs. There is no country nor language restriction, everyone can win a prize. One don't have to have participated in VK Cup to receive the prize. Exact selection algorithm will be announced before the start of the round.

Good luck!

Congratulations to the winners!

Div. 1:

  1. TakanashiRikka
  2. moejy0viiiiiv
  3. Petr
  4. anta
  5. matthew99

Div. 2:

  1. ccz181078
  2. repeating
  3. ioyeoa
  4. ReaLNero
  5. beet

The analysis is here.

The problems correspond to problems of VK Cup 2017 - Finals as follows:

Congratulations to souvenir winners!

Eligible list place Contest Rank Handle
65 830 65 halin.george
69 830 69 Neil
153 830 153 BigBag
265 830 266 whczr
320 830 323 Rydberg

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By KAN, 5 months ago, translation, In English,

Hi!

On Tuesday, July 11, 2017, at 16:35 UTC Codeforces Round #423 will be held. Some of the problems will be from VK Cup 2017 Finals, some are prepared by Codeforces team to complete the problemset.

Note that there will be two rounds based on VK Cup Finals, so I want to ask finalists not to discuss problems until the end of the second round.

There will be six problems in each division, four of them shared. The problems of this round are proposed, prepared and tested by: gritukan, demon1999, fcspartakm, Perforator, MikeMirzayanov, PavelKunyavskiy, qwerty787788, Belonogov, izban, tourist, vepifanov, AlexFetisov, winger, Errichto, Gassa, naagi, ashmelev, Endagorion, ifsmirnov, Arterm and me. Huge thanks to all who helped with the preparation!

There will be prizes from VK social network in this round! Namely, among participants solved five or more problems in second division, or three or more problems in first division, five are to be selected randomly. They will receive championship souvenirs. There is no country nor language restriction, everyone can win a prize. One don't have to have participated in VK Cup to receive the prize. Exact selection algorithm will be announced before the start of the round. There will be prizes in the second round using Finals' problems as well!

Good luck!

Congratulations to the winners!

Div. 1:

  1. W4yneb0t
  2. moejy0viiiiiv
  3. koosaga
  4. Radewoosh
  5. dotorya

Div. 2:

  1. ccz181078
  2. rqy1458814497
  3. houruize
  4. _Is_It_Rated_
  5. liutianyi000

The analysis is here.

Corresponding problems from VK Cup 2017 - Finals:

The souvenirs winners are:

Eligible list place Contest Rank Handle
19 827 19 zeliboba
42 827 42 kevinsogo
114 827 115 triploblastic
125 827 126 lexuanan
138 827 140 alex256

Congratulations!

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By KAN, 5 months ago, translation, In English,

Today, on July 9, 2017 the VK Cup 2017 Finals is being hold in Saint Petersburg!

Just to remind you, the total prize fund is 2490368 rubles, 20 teams consisting of 39 contestants in total will fight for it. Past years champions are tourist and niyaznigmatul in 2015, and tourist and subscriber in 2016. Who is going to take the first place today?

You can watch live results of the competition here, the start is at 08:05 UTC.

Good luck to all contestants and fans!

Final standings

UPD: Hooray! The results of the final competition were summed up. Congratulations to the winners!

  1. ershov.stanislav, aid,
  2. V--o_o--V, LHiC,
  3. enot110, I_love_Tanya_Romanova,
  4. zemen, Zlobober,
  5. nikgaevoy, gnomina007,
  6. RomaWhite, witua,
  7. Trumen, felix,
  8. Rubanenko, MrDindows,
  9. Tima, AKim,
  10. Golovanov399, I_hate_ACM,
  11. Goofy57, Shapo,
  12. ztk, ballon,
  13. Nobik_Glem, Omelianenko,
  14. Seemann, george..s,
  15. Temirulan, aidos.nurmash.
  16. EvErka, greencis,
  17. IlyaLos, extraVirgin20,
  18. YakutovDmitriy, BudAlNik,
  19. Lilith, Copymaster,
  20. SergeiFedorov.


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By KAN, 5 months ago, In Russian,

Ура! В эти выходные, 8-9 июля, в Санкт-Петербурге в главном офисе компании ВКонтакте состоится финал VK Cup 2017!

Лучшие 20 команд по результатам отбора будут соревноваться за звание Чемпиона и солидные денежные призы:

  • 1 место — 1048576 рублей
  • 2 местo — 524288 рублей
  • 3 местo — 262144 рубля
  • 4-8 места — 131072 рубля

В этом году финалистами стали:

  1. zemen (Константин Семенов, Москва), Zlobober (Максим Ахмедов, Москва),
  2. V--o_o--V (Владислав Макеев, Москва), LHiC (Михаил Ипатов, Москва),
  3. RomaWhite (Роман Білий, Львов), witua (Віталій Герасимів, Львов),
  4. YakutovDmitriy (Дмитрий Якутов, Пермь), BudAlNik (Николай Будин, Киров),
  5. Golovanov399 (Александр Голованов, Казань), I_hate_ACM (Никита Уваров, Москва),
  6. Lilith (Анастасия Софронова, Санкт-Петербург), Copymaster (Алексей Гордеев, Санкт-Петербург),
  7. ershov.stanislav (Станислав Ершов, Санкт-Петербург), aid (Айдар Сайранов, Санкт-Петербург),
  8. Tima (Темірлан Сатылханов, Талдыкорган), AKim (Андрей Ким, Талдыкорган),
  9. Nobik_Glem (Владислав Глембоцький, Хмельницкий), Omelianenko (Андрій Омельяненко, Кременчуг),
  10. enot110 (Владимир Смыкалов, Санкт-Петербург), I_love_Tanya_Romanova (Богдан Прищенко, Львов),
  11. Trumen (Тарас Савіцький, Львов), felix (Володимир Радюк, Львов),
  12. SergeiFedorov (Сергей Федоров, Москва) — команда из одного человека!,
  13. IlyaLos (Илья Лось, Саратов), extraVirgin20 (Данил Сагунов, Астрахань),
  14. nikgaevoy (Никита Гаевой, Санкт-Петербург), gnomina007 (Иван Бочков, Ижевск),
  15. Rubanenko (Роман Рубаненко, Кременчуг), MrDindows (Евгений Задорожний, Запорожье),
  16. Seemann (Кирилл Симонов, Санкт-Петербург), george..s (Георгий Струков, Санкт-Петербург),
  17. Goofy57 (Сергей Волнов, Москва), Shapo (Никита Шаповалов, Подольск),
  18. EvErka (Валентин Витязь, Минск), greencis (Иван Лукьянов, Минск),
  19. ztk (Артём Зинченко, Киев), ballon (Іван Здомський, Киев),
  20. Temirulan (Темирулан Мусаев, Алматы), aidos.nurmash (Айдос Нұрмаш, Кызылорда).

Традиционно, за день до Финала пройдет неофициальное соревнование CodeGame Challenge. После четырех часов напряженного контеста все смогут на большом экране наблюдать за тем, кто станет победителем, и, конечно, болеть за свои стратегии!

Зрители смогут наблюдать за соревнованиями по ссылкам, которые добавим чуть позже. А задачи финала можно будет порешать всем желающим в виде раунда Codeforces, который состоится совсем скоро после финала.

Желаю удачи участникам и побольше позитива на туре!

UPD: Результаты пробного тура уже можно наблюдать по ссылке!

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By KAN, history, 6 months ago, translation, In English,

During the discussion after the Round 421 it turned out that the author's solution was wrong. Yes, we had several testers, we had a bruteforce solution that worked correctly, we had a stress testing between the bruteforce and the main solutions. However, all these measures haven't prevented the mistake: the testers haven't noted the issue, the stress haven't found any counter-tests. The solutions also produced the same answers all small tests we had in the testset, so we only found the issue when a test used for a hack was added.

We are terribly sorry about the mistake. We did our best to ensure the problems are ok, I don't know any available method that we haven't used to check the problem.

We've spent the last few hours trying to come up with a new, correct solution to the problem, but right now I don't see any solution that seems undoubtedly correct to me. There are a few that work better than the author's, but yet unproved, you can try to prove this one, for example. I think this problem should be solvable with careful case analysis, and I'm trying to do this right now. I'll post the results here. I'd also be glad if someone post the solution with proof.

Thus, I apologize that the round should be declared unrated. Hope for your understanding.

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By KAN, 7 months ago, translation, In English,
A: Carrot Cakes
B: T-shirt buying
C: Fountains
D: Field expansion
E: Aquarium decoration
F: Beautiful fountains rows
G: Cut the pie

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By KAN, history, 8 months ago, In Russian,

Хочу сказать огромное спасибо fcspartakm, который подготовил задачи и разборы!

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By KAN, 8 months ago, translation, In English,

Hi all!

Tomorrow, on April 5th 2017, at 15:35 UTC the first Wild-card Round of VK Cup 2017 will be held. Along with it there will be parallel unofficial round in which everyone can take part.

The rounds will use special rules, the rounds will be unrated. The problems were prepared by Codeforces team.

The detailed rules will be added to this post 30 minutes before the rounds. I can say now that there will be 24-hours open hacks phase after the round, like in Codeforces Educational Rounds.

Round rules:

The round will be almost usual contest with ACM ICPC rules. There will be 12 problems for 2 hours. During the round your solutions will be tested on some basic tests, they should be much stronger than usual pretests. After the round you will have 24 hours to find tests against other participants’ solutions, this part is the same as in Educational rounds. After that we will add all succesful hacks and our tests and rejudge all submissions. Then the results will be final.

The main difference between ACM ICPC rules and this round is the following rule.

You should submit each problem in a unique programming language. Different compilers of same language are considered the same language. For example, GNU G++, GNU G++ 11, GNU G++ 14 and MS C++ compilers are C++ language. Thus, you are not only to solve problems, but also try different and new for you languages. We don’t think you know 12 languages, we hope that you will quickly learn some basic syntax.

Formally, the following check is performed when you submit a task:

  • If there is at least one submission in queue or submission that passed at least one test for this problem in another language, your solution will be ignored. Thus, if your program passes at least one test, you can only solve this problem using this language.
  • If there is at least one submission in queue or submission that passed at least one test for another problem in same language, your solution will be ignored. Thus, you can’t use a language for more than one problem.

Remember that you can view filter status of some other round by language and view submissions in a specific language. Also, you can view examples of codes in any of the supported languages on the table below. Also, the table contains the groups of compilers considered the same language.

You can use “custom invocation” tab to run a solution if you don’t have the compiler locally.

Language Group Compilers Examples
C GNU C, GNU C11 10903473, 17029870
C++ GNU C+, GNU C++11, GNU C++14, MS C++ 23794425, 5456501
C# Mono C#, MS C# 3195513, 3794163
D D 5482410, 2060057
Go Go 7114082, 21366098
Haskell Haskell 455333, 1668418
Java Java 8 25491359, 23678167
JavaScript V8 6174887, 5743720
Kotlin Kotlin 25779271, 25204556
OCaml OCaml 6157159, 1281252
Pascal Delphi, FPC 1275798, 1259434
Perl Perl 2519448, 1277556
PHP PHP 413942, 4475965
Python Python 2, Python 3 4432133 (Py2), 15729882 (Py3)
Ruby Ruby 1837970, 1289551
Rust Rust 25180002, 24643411
Scala Scala 22577830, 2456025

The main rules of ACM ICPC contest: each problem can either be completely solved (when all tests are passed), or not solved. The participants are ranked by the number of solved problems, in decreasing order, in case of a tie they are ranked by penalty time. The penalty time is the sum among all problems the time in minutes that had passed between the start of the round and the moment the problem got solved, plus 20 minutes for every rejected submission. Note that the problems are not arranged by difficulty. Also, you can resubmit a solution even if it passed all tests, because there will be more tests after the open hacks.

Good luck!

Open hacks phase has ended, the solutions are rejudged. Congratulations to winners!

Official round:

  1. I_love_2007, Ed_Os
  2. VernitaGreen, svxf
  3. gars, Provet
  4. Me-and-Myself, zetilovn
  5. svetlana_lana, GoldenMan

Open mirror:

  1. lewin
  2. Bugman
  3. uwi
  4. ifsmirnov
  5. Tinsane

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By KAN, 9 months ago, translation, In English,

Hello everybody!

The Technocup 2017 (a competition for high-school students hosted by Mail.Ru Group together with MIPT, Bauman MSTU and Codeforces) Finals is happening tomorrow in Moscow. For those who will not participate in the Finals, we prepared mirror contests for both divisions. The round will start at 13:05 UTC at Sunday, March 5th, 2017 and will last for two hours.

The round was prepared by Endagorion, WHITE2302, Alladdin, fcspartakm, Amethyst1, MikeMirzayanov, ifsmirnov and me.

You can view the current onsite results at link.

There will be six problems in each division.

Editorial is here.

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By KAN, 10 months ago, translation, In English,
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By KAN, 10 months ago, In English,

Hi!

The Codeforces Round #398 (Div. 2) is going to be held on Saturday, 18 February 2017 at 9:05 UTC for participants from division 2.

The round is based on XIII Nizhny Novgorod Olympiad in Informatics for high school students named after V. D. Lelyukh, which will take place on Saturday in Nizhny Novgorod. However, not all problems from the Olympiad are included into this round.

The problems were prepared by KAP, ashmelev, ZhNV, kuzmichev_dima, mmatrosov, mike_live, arsor and me.

You will be given two hours to solve five problems. As usual, participants from division 1 can take part out of competition.

Scoring: 500-1250-1500-2000-2500.

UPD: The contest is over, thanks to all who has participated! Congratulations to the winners:

Div. 2:

  1. maryanna2015
  2. imperishableshooting
  3. aquatic
  4. Cth1999
  5. mister_dudec
  6. FallDream
  7. Illidan
  8. Alex342
  9. A.Magdy7 and TmEnd

Div. 1:

  1. eddy1021
  2. HellKitsune
  3. I_love_Tanya_Romanova
  4. gritukan
  5. latte0119

I apologise for the problem difficulty of the problem B, we expected much more accepteds. Hope you liked the problems! The editorial will be posted in 1.5 hours after the Olympiad is finished. Editorial.

We know about the issue with ratings, they will be rolled back and then updated properly. Don't worry.

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By KAN, 10 months ago, In English,

Hi Codeforces!

The Codeforces Round #397 by Kaspersky Lab and Barcelona Bootcamp (Div. 1 + Div. 2 combined) is going to be held tomorrow at 8:05 UTC!

This round is organized in collaboration with Hello Barcelona ACM ICPC Bootcamp 2017 and supported by Kaspersky Lab.

Over 100 students from 17 countries and more than 25 universities such as Cornell University, University College London, École Normale Supérieure, University of Tokyo, Saint-Petersburg State University and Moscow Institute of Physics and Technology gathered in Barcelona to train together for the ACM ICPC Finals.

For eight days students have been solving problems, listening to lectures, learning and making new friends. The training schedule is intense consisting of full-length practice contests, interleaved with one-day educational modules on topics we find especially important. Every contest is followed by an in-depth explanations of every problem and technique encountered in all forms.

It is hard to convey the atmosphere of the event in words. It is said, a picture is worth a thousand words and here is a selection to give you some idea of this fantastic bootcamp. You can see more pictures from the event here and here.

The round authors are Endagorion, ifsmirnov, zemen and Arterm. The round is combined for both divisions, will contain seven problems and last for three hours. Good luck!

UPD: The scoring is 500-1000-1250-2000-2500-3250-3500.

The contest is finished. We hope that you enjoyed it. Congratulations to the winners!

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By KAN, 11 months ago, In English,
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Problem author: KAN.

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Problem author: KAN.

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Problem author: pashka.

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Problem author: Umqra.

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Problem author: Um_nik.

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Problem author: Um_nik.

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By KAN, 11 months ago, In English,

Hi all,

The 8VC Venture Cup 2017 - Final Round is tommorrow at 18:05 UTC. Along with that, Codeforces Round #393 will be held at the same time both for Div. 1 and Div. 2 participants. The Div. 1 Edition will contain the same problems as the Final Round, the Div. 2 Edition will be easier.

Of course, those who have placed in top 200 in 8VC Venture Cup 2017 - Elimination Round should register for the Final Round, all the others should register for Div. 1 or Div. 2 editions according to their rating. All three contests will contain six problems, last two hours and be rated.

The problem authors are Um_nik, Endagorion, Umqra, pashka and me. Also huge thanks to fcspartakm for his help in preparation, and to vepifanov and AlexFetisov for testing the round. I suggest you reading all the problems to find which one you like the most!

I'd like to remind you about the prizes:

  • Overall 1st place — $2000
  • Overall 2nd place — $1000
  • Overall 3rd-5th places — $500 each
  • Overall 1-50th place — t-shirts with 8VC and company logos
  • Local Winner — Dinner with Joe Lonsdale (founder of Palantir, Addepar and 8VC) and other Silicon Valley technologists
  • Local top finishers — Opportunity to meet with leadership from 8VC portfolio companies

Please welcome one more company became interested in the Venture Cup, Progressly!

Progressly is a cloud-based Operational Performance Management platform allows you to document, collaborate on, and gain contextual insights into core business processes and outcomes in real time.

The scoring is usual in all three contests: 500-1000-1500-2000-2500-3000.

Congratulations to the winners!

8VC Vecture Cup 2017 winners:

  1. V--o_o--V
  2. bmerry
  3. Marcin_smu
  4. LHiC
  5. qwerty787788

Codeforces Round #393 Div. 1 winners:

  1. cubelover
  2. RomaWhite
  3. PavelKunyavskiy
  4. snuke
  5. gritukan

Codeforces Round #393 Div. 2 winners:

  1. Kacey
  2. wcx5tq957i
  3. Bekzhan.Kassenov
  4. Tailz
  5. ETA-Mu

Editorial

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By KAN, history, 13 months ago, translation, In English,
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