Hello, Codeforces!

I'm opening an online school for competitive programming!

Every week I'll host:

• A lecture on a topic chosen based on the preferences of participants.
• A long contest, covering difficulties from 2000 to 3000+.
• An editorial for the long contest.

The goal of the classes is to prepare people for OI competitions (i.e. Russian National Olympiad, IOI) and general Codeforces/ICPC contests. If you haven't seen my name before, some of my achievements are second place at IOI, fifth place at Facebook Hacker Cup, and first place at ICPC North American Championship.

The price for the classes is $100 per month, in crypto. If it is too much for you but you still want to participate, hit me up with a short bio/short story about yourself.

There are no limits on the rating of participants, although 1600+ is definitely recommended!

We will start on the 1st of August. You can join for a month at a time, and it is also possible to join later.

If you want to join, fill in this questionnaire.

There is also a possibility for private lessons, for a bit higher price discussed on a personal basis.

If you have any questions, feel free to message me at @illgift in telegram!

UPD: We start next week!

Привет, Codeforces!

Мы приглашаем вас поучаствовать в Good Bye 2021, который пройдет в 29.12.2021 18:35 (Московское время). У вас будет 2 часа на решение задач. Раунд рейтинговый для участников обоих дивизионов.

Задачи были подготовлены 300iq с помощью потрясающих координаторов KAN и 74TrAkToR.

Мы благодарим всех тестеров, без которых этот раунд бы не состоялся: gamegame, thenymphsofdelphi, ko_osaga, golions, Ashishgup, izban, prabowo, 74TrAkToR, Devil, manish.17, taran_1407, minhcool, AlFlen, Utkarsh.25dec, NemanjaSo2005, wxhtzdy, ajit, mnaeraxr, Scrubpai, YashDwivedi, eatmore!

И, конечно, спасибо MikeMirzayanov за потрясающе платформы Codeforces и Polygon.

Этот раунд проходит при поддержке компании NEAR, которую основал бывший участник соревнований AlexSkidanov. В команде, разрабатывающей NEAR, работают многие известные участники сообщества, включая дважды чемпиона мира ICPC eatmore и победителя GCJ и TCO Egor.

В раунде предусмотрены призы для участников, которые займут первые 255 мест. Победитель раунда получит Ⓝ128, участники на втором и третьем месте по Ⓝ64, участники на следующих четырех позициях по Ⓝ32, и т...

NEAR — это современный протокол блокчейна. В прошлом месяце на NEAR запустился проект CrowdForces, который позволяет участникам первого дивизиона получать NEAR за создание простых головоломок. За регистрацию на CrowdForces вы сразу получите 1 NEAR. Подробности здесь: https://nearcrowd.com/crowdforces

Если вы не в первом дивизионе — не беда! Присоединяйтесь к открытому для всех хакатону Metabuild с призовым фондом в $1M. Подробности: https://metabuild.devpost.com/

Надеемся, что вам понравятся задачи! Удачи!

Поздравляем победителей!

1. tourist
2. ecnerwala
3. ksun48
4. Radewoosh
5. Benq

UPD: Разбор

I've created an NFT.

I'll have a private one-hour long call with the person who ends up owning it (if you want, you can also try to resell the NFT instead of claiming the private lesson, I don't really care).

The price is not fixed, feel free to make any offers on the OpenSea. The instructions for the owner are listed in the unlockable conent.

We invite you to participate in CodeChef’s December Long Challenge, this Friday, 4th December, from 15:00 IST onwards. The contest will be open for 10 days i.e. until 14th December.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Joining me on the problem setting panel are:

• Setters: Ildar 300iq Gainullin, Alexander scanhex Morozov, Ivan isaf27 Safonov, Anton antontrygubO_o Trygub, Md. Reyad Fiction Hossain
• Admin : Ildar 300iq Gainullin
• Tester: Alexander scanhex Morozov
• Editorialist: Ajit Sharma ajit Kasturi
• Video Editorialists: Chirayu [user: chirayu_jain98] Jain, Prachi agarwal19 Agarwal, Darshan darshancool25 Lokhande, Yashodhan Agnihotri, Bharat Singla, Aryan Aggu_01000101 Agarwala, Radoslav radoslav11 Dimitrov
• Statement Verifier: Jakub Xellos Safin
• Mandarin Translator: Hanlin Ioser Ren
• Vietnamese Translator: Team VNOI
• Russian Translator: Fedor Mediocrity Korobeinikov
• Bengali Translator: Mohammad solaimanope Solaiman
• Hindi Translator: Akash Shrivastava akashsrivastava143

Prizes:

Top 20 performers in the Indian category and top 10 performers in the Global category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. First to solve each problem except challenge — 100 laddus. Know more here

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Good Luck!
Hope to see you participating!

We invite you to participate in CodeChef’s November Lunchtime, this Saturday, 28th November, from 7:30 pm to 10:30 pm IST onwards 3 hours, 5 problems.

We will also be hosting two live problem discussion sessions on Sunday (29th) from 5pm to 6:30pm IST (first 4 problems) and on Monday (30th) from 5pm to 6:30pm IST (last 3 problems), where our panelist, rajarshi_basu will discuss the Lunchtime problems. Find more details here.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Joining me on the problem setting panel are:

• Setter & Admin: Ildar 300iq Gainullin
• Tester: Nikolay budalnik Budin
• Editorialist: Alei Morphy Reyes
• Video Editorialists: Chirayu Jain, Prachi agarwal19 Agarwal, Darshan darshancool25 Lokhande, Yashodhan ay21 Agnihotri, Bharat Singlai, Aryan Aggu_01000101 Agarwala, Radoslav radoslav11 Dimitrov
• Statement Verifier: Jakub Xellos Safin
• Mandarin Translator: Qingchuan qingczha Zhang
• Vietnamese Translator: Team VNOI
• Russian Translator: Fedor Mediocrity Korobeinikov
• Bengali Translator: Mohammad solaimanope Solaiman
• Hindi Translator: Akash Shrivastava

Prizes: Top 10 Indian and top 10 Global school students from ranklist will receive certificates and CodeChef laddus, with which they can claim cool CodeChef goodies. Know more here. The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Good luck and have fun!

If you are a school student and love programming competitions, enjoy solving mathematical and logical problems, designing, and implementing algorithms and data structures – we invite you to participate in the International Olympiad in Informatics — Innopolis Open.

The contest is one of several international Olympiads annually held by Innopolis University. The best high school students from different countries compete in the prestigious competition to sharpen their informatics skills.

3 steps to win!

• Sign up until November 22, 2020 choosing a category: Informatics. For Russian speaking countries, the registration is here
• Pass the Qualification Online Round. There will be 2 independent online contests, you can participate in both contests. The best result of two contests will be taken to get to the Final Stage.
• • 1st Qualification Online Round: November 22, 2020 at 10:00 a.m. (UTC +3), duration — 5 hours
• • 2nd Qualification Online Round: December 13, 2020 at 3:00 p.m. (UTC +3), duration — 5 hours

• Be on the Final Stage at Innopolis University (we hope it would be on-site, not online) on February 20-21, 2021.

We invite you to participate in CodeChef’s October Long Challenge, this Friday, 2nd October, from 15:00 IST onwards. The contest will be open for 10 days i.e. until 12th October.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here. Joining me on the problem setting panel are:

• Setters: Ildar 300iq Gainullin, Aleksandr enoone Abelyan, Ivan isaf27 Safonov, Chaithanya Dragonado Shyam, John Smith, Md. Reyad Fiction Hossain
• Admin: Ildar 300iq Gainullin
• Editorialist: Jelmer Firet, Srikkanth srikkanthr
• Tester: Radoslav radoslav11 Dimitrov
• Video Editorialists: Chirayu Chirayu Jain, Prachi agarwal19 Agarwal, Darshan darshancool25 Lokhande, Mani manijuana Tyagi, Divesh divesh2201 Thakker
• Statement Verifier: Jakub Xellos Safin
• Mandarin Translator: Hanlin Ioser Ren
• Vietnamese Translator: Team VNOI
• Russian Translator: Fedor Mediocrity Korobeinikov
• Bengali Translator: Mohammad solaimanope Solaiman
• Hindi Translator: Akash Shrivastava

Prizes:

P.S: For October Long Challenge, we won't be having any tie-break Challenge problem. So, instead of giving the usual cash prizes to the top-ranked users, we will give laddus, which help in the fair distribution of reward. For the Indian rank list, we'll distribute 5000 laddus amongst all the top-scorers. For the Global rank list, we'll distribute 13000 laddus amongst all the top-scorers. The top 20 performers in the Indian category and top 10 performers in the Global category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. First to solve each problem except challenge — 100 laddus. Know more here

Good Luck!
Hope to see you participating!

Hello Codeforces!

I became a coordinator of CodeChef Lunchtimes, and we are in need of high-quality proposals.

We hope to get rid of the 'CodeChef has low-quality problems' label.

So we would be grateful if you can provide a problem set that will work fine for the IOI-style contest! (Note that your problems should not necessarily follow the IOI syllabus).

You can read about compensation and the required difficulty of problems here.

Proposals for Lunchtimes should be submitted to the following e-mail: [email protected]

P.S. If you have hard problems for CodeChef Long Challenges, you can send them here

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, Howadji, 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 jqdai0815, ko_osaga, Radewoosh, ksun48, xiaowuc1, ainta, molamola., Endagorion, antontrygubO_o, Rewinding

UPD: Editorial link

Отборочный раунд Engine VK Cup 2019-2020 пройдет 23.02.2020 19:05 (Московское время). Это соревнование предназначено для людей, прошедших квалификацию ранее. Лучшие 40 человек пройдут в финал, который пройдет 11-12 апреля, а лучшие 64 получат футболки VK Cup. Как обычно, параллельно пройдут два обычных раунда, по одному для каждого дивизиона, для тех, кто не может принять участие в этом этапе VK Cup.

Этот раунд бы не состоялся без lperovskaya, MikeMirzayanov, PavelKunyavskiy, izban, Kurpilyansky, YakutovDmitriy, 300iq.

Все три раунда будут идти 2 часа 30 минут, и все являются рейтинговыми. Раунды VK Cup и первого дивизиона будут иметь шесть задач, одинаковые в обоих раундах. Раунд второго дивизиона будет содержать шесть задач. Стоимости задач будут объявлены перед раундом.

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 21.12.2019 14:05 (Московское время). 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 jqdai0815, Claris, quailty, jiry_2 (camp TA team), and gamegame, isaf27, tmwilliamlin168, mango_lassi, WNG, Lewin, sas4eka, UselessDev, 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, jqdai0815, whzzt, sunset, TLE, ko_osaga, rushcheyo, jiry_2, gamegame, Rewinding. 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, jqdai0815, 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.

Привет, Codeforces!

Рад пригласить вас на Codeforces Round 562 (Div. 1) и Codeforces Round 562 (Div. 2), которые пройдут в 26.05.2019 18:35 (Московское время). Раунд будет рейтинговым для обоих дивизионов (^人^).

Участникам обоих дивизионов будет предложено пять задач и два часа на их решение.

Задачи были придуманы и подготовлены мной. Спасибо KAN за помощь с раундом, sunset, TLE, Sulfox, isaf27, Lewin, Aleks5d и wrg0ababd за тестирование и обсуждение задач! А также, спасибо MikeMirzayanov за отличные системы Codeforces и Polygon!

Поздравляем победителей!

Div1:

1) DearMargaret

2) OnionPringles

3) Errichto

4) maroonrk

5) Um_nik

Div2:

1) Szoboszlai10

2) lelolas

3) ndmitrovic

4) prick

5) Stardust

Разбор задач

Добрый день!

6 апреля, в 14:35 UTC+3 состоится Codeforces Global Round 2.

Это второй раунд из серии Codeforces Global Rounds, которая проводится при поддержке XTX Markets. В раундах могут участвовать все, рейтинг тоже будет пересчитан для всех.

Призы в этом раунде:

• 30 лучших участников получат футболки.
• 20 футболок будут разыграны случайным образом среди участников с 31-го по 500-е место.

Призы в серии из 6 раундов в 2019 году:

• За каждый раунд лучшим 100 участникам начисляются баллы согласно таблице.
• Итоговый результат участника равны сумме баллов для четырех лучших выступлений этого участника.
• Лучшие 20 участников по итоговым результатам получают толстовки и сертификаты с указанием места.

Задачи для этого раунда были разработаны целым коллективом авторов: 300iq, cyand1317, Aleks5d, RDDCCD, KAN, gen.

Спасибо KAN за помощь в координации раунда, а также isaf27, Lewin, ----------, Errichto, arsijo, cdkrot за тестирование!

Удачи!

Поздравляем победителей!

1) ecnerwala

2) tourist

3) Um_nik

4) Endagorion

5) Petr

Разбор задач.