Hello, codeforces!

All signs in the sky and on the ground indicate that you've enjoyed my first blog, so here is the second one. I've decided to choose a Polish task again, as there are plenty of interesting ones. This time we'll take a look at the "plot purchase" (you can submit here), which is a bit easier, but a few years ago I was very proud of myself when I solved it. The statement goes as follows:

You are given a square n × n grid (1 ≤ n ≤ 2000). In every cell, there is a number from the range [1, 2·10⁹]. You are also given an integer k (1 ≤ k ≤ 10⁹). A task is to find a subrectangle of this grid such that the sum of values in this subrectangle lies in the range [k, 2·k] (or report that there is no such subrectangle). Just print coordinates of its opposite corners.

Hello, codeforces!

The community wants so the community gets it! :D Here it is, my very first blog about tasks and algorithms. At the beginning I've decided to post my entries on codeforces, maybe I'll switch to something different if it becomes uncomfortable.

To pour the first blood I decided to choose a task from one of the old ONTAK camps. Task's name is "different words" (you can submit here). The statement goes as follows:

You are given n words (2 ≤ n ≤ 50 000), every of length exactly 5 characters. Each character can be a lowercase letter, an uppercase letter, a digit, a comma... basically, it can be any character with ASCII code between 48 and 122 (let's say that k is the number of possible characters). A task is to find all pairs of indexes of words which are . Two words are if they differ at all 5 corresponding positions. So for example words and are really different and words and are not, because in both of them the third character is . As there can be many such pairs (up to ), if there are more than 100 000 pairs, then the program should print that there are only 100 000 and print this number of pairs (arbitrary chosen).

Please, note that this task comes from the contest which took place a few years ago, so don't think about bitsets. :P

Important day! Today we will know the winners of VK Cup 2018. The prize fund of the competition — numbers in binary notation:

• 1 place — 1048576 rubles
• 2 place — 524288 rubles
• 3 place — 262144 rubles
• 4-8 place — 131072 rubles

We are start at 10:40. Monitor the progress here.

1. 120 Minutes Adventure: el_sanchez, SpyCheese
2. я и моя девушка: aid
3. Нижний Магазин SU: V--o_o--V, LHiC
4. Road to the Gucci store: Golovanov399, -imc-
5. Ананас: AllCatsAreBeautiful, arsijo
6. Accepted, cats and dogs: Andrew_Makar, BigBag
7. ИТМО 2.0: craborac, demon1999
8. Pareidolia: Copymaster, Lilith

The first day of every year championship for programming VK Cup 2018!

Today VK Cup was opened by Alexander Konstatinov (VK) and Mikhail Mirzoyanov (CodeForces). After that was a non-formal part, there we looking for funny photos of our competitors and know some interesting facts about them.

Some teams from the top-20 of Round 3 have refused to participate in the final to save the chance for the next year. We invited the following by rating. So, this year's finalists, meet!

1. Нижний Магазин SU: V--o_o--V & LHiC
2. ИТМО 2.0: craborac & demon1999
3. 120 Minutes Adventure: el_sanchez & SpyCheese
4. Кекс столичный: Melnik & hloya_ygrt
5. Z: egor_bb & Nikitosh
6. Saint Veronika: aytel & kokokostya
7. Road to the Gucci store: Golovanov399 & -imc-
8. Группа внутренних автоморфизмов: MrKaStep & bixind
9. Keksik: Tinsane & kb.
10. Свист минигана: Sert & Alexandr_TS
11. Ананас: AllCatsAreBeautiful & arsijo
12. Pareidolia: Copymaster & Lilith
13. я и моя девушка: aid
14. Типичная вечеринка с бассейном: Au-Rikka & Seemann
15. Accepted, cats and dogs: Andrew_Makar & BigBag
16. Московский Вентиляторный Завод: Дудка и Трубник: mHuman & komendart
17. QuietGenius: Semenar & Vaterlou
18. Влюбленные Мудаки: super_azbuka & Khusainov
19. R3tired: totsamyzed
20. Вупсень и Пупсень: Roms & adedalic

Trial round reviewed our system — trial round! The first problem of trial round was a quiz. The question was about Codeforces and VK. First team that solved it is Saint Veronika: kokokostya, aytel. Сongratulate! :)

Yesterday finalists went to the Hermitage Museum and carting. Today we had a lunch on the ship.

Competitors now take part in Code Game Challenge. In 2018 this is football. At evening we will watch results. For winners, VK has very nice prizes.

Tomorrow we give a link to results and you can watch and chatter for the favorite teams ;) More about the competition you can watch at VK Cup group.

Hi!

Summer Informatics School (SIS / LKSH) is a summer school for students in grades 6-10. SIS is focused mainly (but not only) on students participating in the Olympiads in Informatics — from beginners to participants of international competitions. SIS is held in July and August, each of them is visited by about 200 students from all over Russia and abroad. The language of the camp is Russian. Additional information about SIS is posted at lksh.ru

Right now, the August branch of the Summer Computer School is running, and on August 11 the traditional team Olympiad is going to place. I am happy to present a rated round based on it!

The round will be rated for both divisions, will be held in Aug/11/2018 16:35 (Moscow time), in each division there will be 5 tasks and 2 hours to solve them.

The problems of this round and the SIS olympiad were authored and prepared by SIS's teachers: izban, achulkov2, Schemtschik, peltorator, craborac, asokol, Morokei, Burunduk2. Also, I would like to thank Kurpilyansky for his help with olympiad's organization.

Thanks to our problems testers: meshanya, Burunduk2, vintage_Vlad_Makeev, niyaznigmatul, manoprenko!

Thank you, MikeMirzayanov, for the codeforces and polygon systems!

Yes, we are aware, that this contest clashes with ProCon Junior on codechef. However, given the schedule of the SIS and the approaching VK cup finals we can't do anything with it, sorry for that =/

Good luck!

UPD: The round will have one interactive problem for both divisions. Please, read the post about interactive problems here: Interactive Problems: Guide for Participants.

Congratulations to winners!

Div1:

1. Marcin_smu
2. Radewoosh
3. Swistakk
4. Panole233
5. ko_osaga

Div2:

1. wnsh
2. aurelio
3. usachevd0
4. jebouin
5. etiennerossignol

Upd Thank you for participation! Due to vk-cup conduction rating recalculation will happen slightly later, than usually.

Upd The editorial is published!

You may also check the unofficial editorial, written by neal.

This round is in memory of Leopoldo Taravilse.

Leopoldo Taravilse (ltaravilse) was a distinguished member of the competitive programming community in Argentina and Latin America. As a contestant, he reached the ACM-ICPC World Finals in 2010 and 2012, and was active in CodeForces and TopCoder. After 2012 he became a problemsetter for the ACM-ICPC South American regionals and the Argentinian Programming Tournament, and later coach for a World Finalist team in 2016.

Leopoldo's passion was helping others realize their full potential in competitive programming. He taught at various competitive programming schools in Brazil, Cuba, Peru and Bolivia, and his role organizing the Argentinian Training Camp cannot be overstated. Under his wing, it grew from a small group of friends in 2010 to a major event featuring international sponsors and having hundreds of participants coming from all corners of Latin America. Through successive editions of the Training Camp, Leopoldo inspired students to learn and improve, to give back to the community, and to have fun doing it.

With his intelligence, warm heart, relentless work ethics and witty sense of humour Leopoldo touched countless lives. We will miss him as a friend, a mentor, a teammate, a drinking buddy, a role model, an overall great person.

Rest in peace my dear Leo.

You can see this blog: A round in the name of ltaravilse.

And you can donate for prizes of this round: In Memory of Leopoldo Taravilse.

Hello everyone!

I'm pleased to announce: Codeforces Round #502!

This round will take place on Aug/08/2018 17:05 (Moscow time). It is rated for all participants and everyone will have 8 problems and 2 hours 15 minutes to solve them.

The contest is created by Magolor. This is the first competition I proposed. I hope that you will enjoy it. The heroes are from a TV show that I like and do not have any relation to Leopoldo.

6 of the 8 problems are created by myself. Thanks to:

• ODT for inspiring me and discussing the problems with me.
• Anton arsijo Tsypko for examining my problems, helping me a lot on this contest and designing problems B and G.
• Max MaxZubec Zub, Danya danya.smelskiy Smelskiy, Sofia Sonechko Melnyk, Stanislav stanislav.bezkorovainyi Bezkorovainiy, Vitaliy kuviman Kudasov, Aleksandr Kostroma Ostanin, for testing the round and improving the problems and solutions.
• Mike MikeMirzayanov Mirzayanov for Codeforces, Polygon and the help he offered to me.
• Nikolay KAN Kalinin for helping with the contest and designing problem G.
• Ahmed ahmed_aly Aly for his initiative to host this round in memory of Leopoldo.

...Yet Another Chinese Round...?

Scoring distribution: 500-1000-1500-1500-2000-2500-3000-3250.

Prizes distribution: $153 for top 30, delivered using bitcoin or amazon gift card (each contestant chooses).

UPD1: Chinese Editorial is published. You can view it through This link. English Editorial well be published soon.

UPD2: Congratulation to winners!

1. Benq

2. 000000

3. webmaster

4. Swistakk

5. orbitingflea

6. ivan100sic

7. ko_osaga

8. dreamoon_love_AA

9. TLE

10.step_by_step

UPD3: English Editorial is published.

On Aug/03/2018 17:45 (Moscow time) Educational Codeforces Round 48 will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extented ACM ICPC rules. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 7 problems and 2 hours to solve them.

The problems were invented and prepared by Ivan BledDest Androsov, Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov and me.

Good luck to all participants!

Congratulations to the winners:

Congratulations to the best hackers:

And finally people who were the first to solve each problem:

UPD: Editorial

Hi all!

The main phase of Codeforces Marathon Round 2 has ended. In the preliminary standings, contestants Rafbill and hakomo have got very close results, at the same time getting far enough from the next group of contestants. Will they manage to maintain the lead after the final testing, and who will come out on top? We will know in a few hours.

For now, I encourage the contestants to share their solution ideas in the comments below, or in separate posts.

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Hello!

Codeforces Round 501 (Div. 3) will start at Jul/31/2018 17:35 (Moscow time). You will be offered 6 or 7 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to my good friends Mikhail awoo Piklyaev, Maksim Neon Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

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I also would like to say that participants who will submit wrong solutions on purpose and hack them afterwards (example) will not be shown in the hacking leaders table.

UPD1: Editorial is published.

UPD2:

Congratulations to the winners:

Congratulations to the best hackers:

604 successful hacks and 446 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem: