November 6–13, 2018 the boot camp for competitive programming Moscow International Workshop ICPC will be held at MIPT. We invite students to participate from all over the World!

The International workshop helps students to prepare for the regional contests and World Finals of the ICPC championship.

The official language of educational program is English. The trainings include every-day contests, tasks analysis and lectures from coaches from former participants and winners of ICPC and the best Russian universities professors. Program includes interesting entertainment program in a free time. Training will be conducted in two divisions:

Division A is designed to prepare students to participate and win medals in the next ICPC World Finals.

Division B is designed to help teams prepare for the regional and international competitions.

Contests are moderated by Oleg Khristenko: coordinator of the Pankratiev Open Cup and the main editor of Snarknews. Heads of Programming Community are Mikhail Tikhomirov and Gleb Evstropov.

The sooner the payment is made, the lower the cost of participation become. Citizens of the Eurasian Economic Union (EAEU) countries may pay in Rubles and others in American Dollars. This cost includes the academic curriculum, catering, accommodation on the MIPT campus, as well as excursions, sportive activities, collective games in the days-offs.

Cost per person: $630 USD until September 21. Two teams have an opportunity to take part in the workshop for free – learn more about it on the site.

Register for Moscow International Workshop ICPC and win!

Hello, codeforces!

This time I've decided to choose a task from my own contest which took place last April and was known as the Grand Prix of Poland. If you want to write this contest virtually in the future, then consider not reading this blog. If you've participated in this contest and maybe even solved this task, then anyway I recommend reading it, cause this task has many very different solutions, each of them being very interesting (in my opinion). It's also a reason why this blog is longer than previous ones.

I'll write about task C "cutting tree" (not uploaded to the ejudge yet :/). The statement goes as follows:

You are given a tree with n vertices (1 ≤ n ≤ 2·10⁵). The task is to calculate f(k) for each integer k from the range [1, n] where f(k) is defined as the maximum number of connected components of size k which we can "cut off" from the tree. A connected component of size k is a set of k vertices such that it's possible to traverse in the tree between any pair of these vertices using only vertices from this set. Chosen components are not allowed to intersect, so each vertex must belong to at most one component.

#IjustWantContribution

It seems there isn't any blog about Berlekamp-Massey Algorithm around here, so I decided to go on a try. :P

Acknowledgement: Hats off to matthew99 for introducing this algorithm.

What is 'linear recurrence'?

Assuming there is a (probably infinity) sequence a₀, a₁...a_n - 1, we call this sequence satisfies a linear recurrence relation p₁, p₂...p_m, iff . (Obviously, if m ≥ n any p can do :P)

How to calculate k-th term of a linear recurrence?

For a polynomial , we define .

Obviously G satisfies G(f) ± G(g) = G(f ± g).

Because , if we let , then G(f) = 0. Also G(fx), G(fx²)... = 0. So G(fg) = 0 (g is any polynomial).

What we want is G(x^k). Because G(f⌊ x^k / f⌋) = 0, then .

Hello.

On Aug/19/2018 16:35 (Moscow time), Codeforces Round #505 takes place. This is a paired round to #504.

Some problems are taken from VK Cup 2018 Finals (ashmelev, Errichto, lewin) and some are proposed by me. I'd like to thank my fellows — Dima (_kun_) who is actually coordinating this round, Kolya (KAN) who brought me here, and also Grisha (gritukan) and Ildar (300iq) just for being nice.

I'd also like to express my gratitude to MikeMirzayanov for multiple bug fixes and awesome Codeforces!

There will be seven problems will the following scoring:
500 — 1000 — 1500 — 1750 — 2250 — 2750 — 3500

UPD. The system testing is over. Editorial (with problem E now)

Congratz to the winners!

1. Swistakk (after all these years, yay)
2. CongLingDanPaiShang3k5
3. Kostroma
4. Benq
5. AwD
6. xumingkuan
7. mcfx
8. fjzzq2002
9. Egor
10. kriii

As in the previous round, thanks to VK social network, GP30 scores will be distributed among the best participants.

Participants are sorted by sum of points for both rounds (if the participant did not participate in one of the rounds, the points scored for it are assumed to be equal to zero), with the maximum time for both rounds from the beginning of the round to the last submission that passed the pretests as tie-break.

Let me remind you that top 10 participants with respect to GP30 score will receive a plush Persik.

Hope you enjoy. Good luck and have fun!

On Aug/18/2018 17:35 (Moscow time) Educational Codeforces Round 49 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. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. 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 Vladimir Vovuh Petrov, Adilbek adedalic Dalabaev, Ivan BledDest Androsov, Mike MikeMirzayanov Mirzyanov and me.

Good luck to all participants!

Our friends at Harbour.Space also have a message for you:

Hi Codeforces!

Our Hello Barcelona Programming Bootcamp will be kicking off next month from Sept 26 — Oct 4, and we’d love to see you there!

The boot camp will once again feature the all-time greats Mike MikeMirzayanov Mirzayanov, Andrey andrewzta Stankevich, Michael Endagorion Tikhomirov, Gleb GlebsHP Evstropov, Artem VArtem Vasilyev, Ivan ifsmirnov Smirnov and other world renowned Russian coaches to train the participants.

You will be competing and learning side by side with some of the greatest teams in the world, while learning from the best coaches the ICPC has to offer.

Be sure to register before September 1st so everyone has time to get visas if needed, and of course for the Early Bird Discount of 5% or the Loyalty Discount* of 20% off registration for the boot camp!

*The loyalty discount is offered to universities and individual participants that took part in Hello Barcelona Bootcamps and Moscow Workshops ICPC.

Learn more about Barcelona ICPC Bootcamp

You can ask any questions by email: hello@harbour.space

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: The editorial is posted

Hi!

August 17, Aug/17/2018 17:35 (Moscow time), there will be a rated Codeforces round #504. Some of the problems will be from VK Cup 2018 finals, and PikMike and Vovuh have prepared other tasks for the full round.

The problems of this round are proposed, prepared and tested by: MikeMirzayanov, PikMike, Vovuh, Errichto, lewin, Endagorion, Um_nik, YakutovDmitriy, BudAlNik, izban, Belonogov, scanhex, 300iq, qoo2p5, Livace.

There will be prizes from VK social network in this round as well! The participants who took the first 30 places of this round and the round #505, also partially based on the tasks of VK Cup 2018 Finals, will get GP30 points.

Participants are sorted by sum of points for both rounds (if the participant did not participate in one of the rounds, the points scored for it are assumed to be equal to zero), with the maximum time for both rounds from the beginning of the round to the last submission that passed the pretests as tie-break.

The top 10 participants will receive a plush Persik!

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!

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.

Good luck to the competitors! At the evening I add the results in this post.