I won't hold any coding streams in May.

Hi!

On Mar/19/2020 17:35 (Moscow time) we will host Codeforces Global Round 7.

It is the first round of a 2020 series of Codeforces Global Rounds. The rounds are open for everybody, the rating will be updated for everybody.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2020:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

The problems of this round were developed by isaf27 and me. Thanks to the testers mohammedehab2002, Taran_1407, Aleks5d, Endagorion, 74traktor, HIR180, dlwocks31,ToTheMoon, coyorkdow, Tzak, DomiKo, JustasLe, Hyado, Nemo, tattosha_aptan, Jatana, and (language corrector!) caoash.

Thanks to XTX, which in 2020 supported the global rounds initiative!

Good luck!

UPD: Score distribution: 500 1000 1000 (1000-1000) 2500 (2000-1500) 4000

UPD: Editorial!

You are given a string $$$s$$$, and for each $$$r$$$ you need to find the largest $$$L_r$$$, such that $$$s[r - L_r + 1 \ldots r]$$$ is a palindrome.

It is possible to solve this problem with the eertree or with Manacher's algorithm with some data structures, but I will describe a simpler way.

You will need some black box, that for any substring $$$s[l \ldots r]$$$ can check in $$$\mathcal{O}{(1)}$$$ if it is a palindrome. The easiest such black box is a polynomial hash, but also you can precalculate stuff from Manacher's algorithm and then check that $$$\frac{(l+r)}{2}$$$ is a middle of a long enough palindrome.

The key fact here is that $$$L_i \leq L_{i-1} + 2$$$, because if $$$s[l \ldots r]$$$ is a palindrome, then $$$s[l+1 \ldots r-1]$$$ is a palindrome too.

With this observation, we can use our black box to find the required values!

Let's assume that you already know $$$L_1, L_2, \ldots, L_{i-1}$$$ and we want to calculate $$$L_i$$$.

Starting from $$$L_i = L_{i-1}+2$$$, decrease $$$L_i$$$ while $$$s[i - L_i + 1 \ldots i]$$$ is not a palindrome.

The number of black box operations of this algorithm is $$$\sum{(L_{i-1} + 2 - L_i)}$$$ $$$\leq 2 n$$$.

Hello everyone, this winter at Petrozavodsk was my third (Petrozavodsk) contest, now it is loaded on the gym.

Contest link.

Virtual participation link.

Thanks to the testers MiFaFaOvO, ko_osaga, Radewoosh, ksun48, xiaowuc1, ainta, molamola., Endagorion, antontrygubO_o, tEMMIE.w.

UPD: Editorial link

The elimination round of Engine VK Cup 2019-2020 will take place at Feb/23/2020 19:05 (Moscow time). This contest is intended for people who qualified earlier.

As usual, there will be two parallel rounds, one for each division, for everybody who can't take part in official round.

Thanks lperovskaya, MikeMirzayanov, PavelKunyavskiy, izban, Kurpilyansky, YakutovDmitry, 300iq for preparing the contest.

All three rounds will last 2 hours 30 minutes, and they will be rated. They will have six tasks, and you will be able to see the score distribution when the round starts.

Hello, Codeforces community!

I'm glad to invite you to Codeforces Round #609 (Div. 1) and Codeforces Round #609 (Div. 2), which will be held on Dec/21/2019 14:05 (Moscow time). The round will be rated for both divisions.

The problems were taken (mostly) from the ByteDance — Moscow Workshops Online Contest, that's happening at the same time. They were prepared by myself and tested by wxhtxdy, Claris, quailty, jiry_2 (camp TA team), and gamegame, isaf27, tmwilliamlin168, mango_lassi, WNG, lewin, sas4eka, Feynman, Aleks5d,MrDindows.

ByteDance is a technology company operating a range of content platforms that inform, educate, entertain and inspire people across languages, cultures, and geographies. ByteDance has partnered with Moscow Workshops ICPC and Codeforces to organize a top tier and exclusive training camp for the International Collegiate Programming Contest. The upcoming Programming Camp will be held in Beijing from February 10th to 16th, 2020.

ByteDance — Moscow Workshops Online Contest is an opportunity to participate as teams in this camp.

You can find more information about this training camp, including registration and prizes at https://programcamp.bytedance.com/.

UPD: Editorial

Hello, everyone!

I think that you often have something to ask or discuss advanced CP topics or some OpenCup rounds or hard problems, and it is not worth creating new codeforces blog, but current popular places with CP chats (i.e OJ chats, or discord, or some country-local chats) are too local and don't have too many people with who you can divide your discussion.

So, I come up with the idea and talked with some of my friends, that it would be cool to create telegram chat with some lower bound on the rating to join.

Now I suggest a lower bound 2600 on rating.

I. e. if you want to join the chat, and if your MAX rating is at least 2600 (so if at some point you had IGM rank), you can write me your telegram login in personal messages, and I will add you to the chat.

Of course, the lower bound may be adjusted later. And if you have suggestions about the proper places for creating this chat, you can write them in comments :) (don't worry, telegram is very convenient!)

Hello everyone, this summer at Petrozavodsk was my second ICPC contest, now it will be held as OpenCup round.

XX Open Cup Grand Prix of Kazan takes place on Sunday, September 8, 2019, at 11:00 AM Moscow time

The link to the contest. You need an Open Cup login to participate.

To ensure Codeforces traditions, I will say thanks to the testers Benq, wxhtxdy, whzzt, sunset, TLE, ko_osaga, rushcheyo, jiry_2, gamegame, CauchySheep. Also thanks to izban with help in tasks choosing.

UPD: Now the contest is loaded to the gym!

Hello everyone, this winter at Petrozavodsk was my first ICPC contest, now it is loaded on the gym.

Contest link.

Virtual participation link.

To ensure Codeforces traditions, I will say thanks to the testers TLE, whzzt, sunset, wxhtxdy, isaf27. Also thanks to izban with help in tasks choosing.

And of course, thanks to MikeMirzayanov for Codeforces and Polygon platforms and help with loading this contest to the gym.

Hi!

I'm glad to invite you to take part in Codeforces Round #562 (Div. 1) and Codeforces Round #562 (Div. 2), they will be held in May/26/2019 18:35 (Moscow time). The round will be rated for both divisions (^人^).

Participants in each division will be offered five problems and two hours to solve them.

The problems were written and prepared by me. Thanks to KAN for his help with the round, to sunset, TLE, Sooke, isaf27, Lewin, Aleks5d and wrg0ababd for testing and task discussing! Also, thanks to MikeMirzayanov for amazing systems Codeforces and Polygon!

Congratulations the winners!

Div1:

1) Vn_nV

2) OnionPringles

3) Errichto

4) maroonrk

5) Um_nik

Div2:

1) soros666

2) lelolas

3) ndmitrovic

4) prick

5) qk0qhh

Editorial

Hi!

At Apr/06/2019 14:35 (Moscow time) we will host Codeforces Global Round 2.

It is the second round of a new series of Codeforces Global Rounds supported by XTX Markets. The rounds are open for everybody, the rating will be updated for everybody.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2019:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

The problems of this round were developed by a team of authors: 300iq, cyand1317, Aleks5d, RDDCCD, KAN, gen.

Thanks KAN for his help in the round's coordination, and also isaf27, lewin, osaaateiasavtnl., Errichto, arsijo, _kun_ for testing the round!

Удачи!

Congratulations the winners!

1) ecnerwala

2) tourist

3) Um_nik

4) Endagorion

5) Petr

Editorial.

Hello, Codeforces community!

Today will be a new useless stream from me, I will write UOJ 90. (I don't know how long it will take to write this problem, I've just found Los_Angelos_Laycurse comment where he said that he has 1000+ lines).

I hope I will start around 22:35 UTC+3 (so it's 50 minutes from the moment of writing the post).

Now my stream will have a webcam and donate notifications!

https://www.twitch.tv/ccciq

Hello everybody!

Now the winter SIS (Summer Informatics School) is taking place, and we, as part of the parallel A+ with its teachers, have prepared a complete Codeforces Round.

The round will happen at Jan/05/2019 19:35 (Moscow time) and will last for 2.5 hours. There will be 6 problems in each division.

The tasks of the round were invented and prepared by 300iq, scanhex, cookiedoth, allrats, osaaateiasavtnl., Qlukva, Forestryks, Dimon, LordVoldebug, romanovsavelij, golub, ismagilov.code,alexey_kuldoshin, LadyPython, UnstoppableSolveMachine under the guidance of teachers izban, VArtem, _meshanya_, pashka.

Also thanks for testing isaf27, isaf27_loves_me, Kurpilyansky.

And, of course, thanks to MikeMirzayanov for great systems Codeforces and Polygon.

Good luck everybody!

UPD: Since the registration opens before the recalculation of the rating after Hello 2019, in case of a division change, the participants will be moved to another division.

UPD: Editorial.

Hello! There will be useless stream from me (I just want contribution, if you want something educative watch someone else).

I will write some very shitty task (without any templates!) without comments (because all what I can say in these moments is some Russian bad words).

I hope that almost every week I will write some ghoulish task (on the stream, of course)...

If you have something to suggest, write it in the comments ;)

If I don't become the legendary grandmaster before the new year, I’ll dye my hair pink for a week.

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!

Less than month left before IOI. Let's share our opinions. I think grumpy_gordon is going to win.

Hello everybody!

On July 28 and 30 will take place tours of EJOI — individual programming competition for juniors, held under the rules of the International Olympiad in Informatics.

EJOI consists of the most interesting and hard problems that are proposed by a wide community of authors, and that is why we decided to give you an opportunity to crack the complete problemset of the contest. During the second tour of Olympiad, we are going to conduct a rated Codeforces round based on problems of both days of our Olympiad.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of EJOI (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

The round will happen at Jul/30/2018 11:15 (Moscow time) and will last for 2.5 hours. There will be 6 problems in each division.

The tasks of the round were invented and prepared by tourist, PavelKunyavskiy, niyaznigmatul, 300iq, GlebsHP, pashka, qoo2p5, VArtem, demon1999, flyrise, ifsmirnov, isaf27, yeputons, _kun_.

Also thanks for testing grumpy_gordon, gritukan, izban, GoToCoding, Egor, dan.io, Sert, disa, alkurmtl, senek_k, BudAlNik.

And, of course, thanks to MikeMirzayanov for great systems Codeforces and Polygon.

Good luck everybody!

UPD: Congratulations to winners!

D1:

1) Um_nik

2) LHiC

3) dacin21

4) ksun48

5) Swistakk

D2:

1) AmirHosseinGorzy

2) WaldarDoppen

3) IHaveHir

4) cly_none

5) Shadi.Gh

Author — gritukan

Author — MikeMirzayanov

Author — 300iq

Author — _kun_

Author — _kun_

Author — _kun_

Author — 300iq

Thank you for your participation, see you soon (I hope)!

Hi!

I'm glad to invite you to take part in Avito Code Challenge 2018 which starts on May/27/2018 17:50 (Moscow time). Any participant can join the round and it will be rated for each participant. Hope to see you among the participants!

Problems are prepared by me — Ildar Gainullin.

This round is conducted on the initiative and support of Avito. Avito.ru is a Russian classified advertisements website with sections devoted to general good for sale, jobs, real estate, personals, cars for sale, and services. Avito.ru is the most popular classifieds site in Russia and is the third biggest classifieds site in the world after Craigslist and the Chinese website 58.com.

Many thanks to Vladislav winger Isenbaev, Grigory gritukan Reznikov, Ivan isaf27 Safonov，Alexander AlexFetisov Fetisov and Shiqing cyand1317 Lyu for the round testing, Nikolay KAN Kalinin for helping me to prepare the contest, and also to Mike MikeMirzayanov Mirzayanov for systems Codeforces and Polygon.

Participants will be offered eight problems and three hours to solve them. Scoring will be announced a bit later.

Avito presents nice gifts for participants. Top 30 participants and also 10 random participants with places 31-130 will be awarded with a special T-shirt.

I hope everyone will find interesting problem for themselves. Wish everyone a successful round and high ratings!

Good luck!

UPD，Scoring： 500 750 1250 1750 2250 2750 3250 3750

UPD，Editorial is ready： Editorial!

The winners of random t-shirts are: