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:

Hello CodeForces Community!

The month of April held a special significance in the programming world, with the ACM-ICPC World Finals crowning a new world champion. So how about you cap off this brilliant month with Chef’s next contest, the April Lunchtime 2018 and join your fellow programmers and enjoy the contest problems.

Joining me on the problem setting panel are:

• Problem Setters, Editorialists and Russian Translators: 300iq (Ildar Gainullin), altruist (Denis Anischenko)
• Problem Tester: kingofnumbers (Hasan Jaddouh)
• Statement Verifier: Xellos (Jakub Safin)
• Mandarin Translator: huzecong (Hu Zecong)
• Vietnamese Translator: VNOI Team

I hope you will enjoy solving them. Please give your feedback on the problem set in the comments below, after the contest.

Contest Details:

Time: 28th April 2018 (1930 hrs) to 28th April 2018 (2230 hrs). (Indian Standard Time — +5:30 GMT) — Check your timezone.

Contest link: https://www.codechef.com/LTIME59

Registration: You just need to have a CodeChef handle to participate. For all those, who are interested and do not have a CodeChef handle, are requested to register in order to participate.

Prizes: Top 10 performers in Global and Indian category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. Know more here: https://www.codechef.com/laddu. (For those who have not yet got their previous winning, please send an email to winners@codechef.com)

Good Luck!
Hope to see you participating!!
Happy Programming!!

На контесте в ЛКШ зашел следующий алгоритм:

Шафлим полуплоскости, перебираем пару, находим точку пересечения, бежим по всем полуплоскостям, когда встречаем полуплоскость в которой эта точка не лежит -> break; Дальше строим выпуклую оболочку всех точек, которые лежат во всех полуплоскостях.

Полуплоскостей было <= 2000.

Слабые тесты или матожидание времени работы быстрее куба?

Hello CodeForces Community,

I take this opportunity to cordially invite you to take part in the CodeChef May Lunchtime. It is an IOI Style contest which will last for 3 hrs.

The problems were set by gainullin.ildar (Ildar Gainullin) and tested by adamant (Alexander Kulkov) & Xsquare (Prateek Gupta). The rest of the panel members include:

• Russian Translator: CherryTree (Sergey Kulik)
• Mandarin Translator: huzecong (Hu Zecong)
• Vietnamese translators: VNOI team

We hope you will enjoy the problems and welcome your feedback in the comments below.

Time: Saturday, 27th May, 2017 at 19:30 HRS — 22:30 HRS. (Indian Standard Time +5:30 GMT) Check your timezone here.

Contest link: https://www.codechef.com/LTIME48

Accepted Languages: https://www.codechef.com/wiki/list-compilers

Registration: You just need to have a CodeChef handle to participate. For all those, who are interested and do not have a CodeChef handle, please register here in order to participate.

Prizes: Top 10 performers in Global and Indian school category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies. Know more here: https://www.codechef.com/laddu. (For those who have not yet got their previous winning, please send an email to winners@codechef.com)

Good Luck! Hope to see you participating!!

Hi!

On April 23, 19:35 MSK will be held rated Tinkoff Challenge – Elimination Round.

Problems were prepared by me — Ildar Gainullin, Alexander alkurmtl Kurilkin and Nikolay KAN Kalinin.

Big thanks to Vladislav winger Isenbaev and Alexander AlexFetisov Fetisov for testing round, and also to Mike MikeMirzayanov Mirzayanov for systems Codeforces and Polygon.

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

This round is eliminational for Tinkoff Challenge.

Best 30 participants will be awarded with warm vests and other pleasant souvenirs like stickers and notepads. Best 100 participants will be invited to Moscow to visit Tinkoff's office with panoramic view on the city.

Best 20 participant who will be able to arrive will advance to Tinkoff Challange – Final Round.

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

UPD. Scoring: 500 1000 1500 2000 2500 3000 3500

UPD. Editorial

Интересно, но на codeforces нельзя поискать слово string. Кто знает, почему так?

Интересно, но на codeforces нельзя поискать слово chess. Кто знает, почему так?

Please, help me to solve this problem https://ru.kattis.com/problems/fenceortho, i know that i can use Rotating Calipers method, using 4 calipers, but i can't intersect them.

I write calipers method storing point and angle of caliper, please help me how to find intersection point of 2 calipers.

Сan you please tell the basic principle of solving such problems with mincost. And please write problems that are solved by this method. for example BubbleCup, task G was one of these.

Здравствуйте, на сайте есть множество задач в которых применимо Convex Hull Trick, но где о нем можно прочитать на русском языке я так и не нашел. Знающие люди, подскажите пожалуйста, где можно прочитать о CHT на русском языке?