Hi all!

This weekend, at Oct/25/2020 14:05 (Moscow time) we will hold Codeforces Round 679. It is based on problems of Technocup 2021 Elimination Round 1 that will be held at the same time.

Technocup is a major olympiad for Russian-speaking high-school students, so if you fall into this category, please register at Technocup 2021 website and take part in the Elimination Round.

Div. 1 and Div.2 editions are open and rated for everyone. Register and enjoy the contests!

The Elimination Round authors are AndreySergunin, Endagorion, amethyst0, and me, Golovanov399. Thanks to KAN and 300iq for their coordination. This round would also be not possible without the help of our testers: __rkm__, 300iq, arjunsanjeev7, brunomont, Chocobar, iankury, low_, psevdoinsaf, scnucjh, and teapotd, thank you so much!

Have fun!

The Elimination Round will feature 6 problems, preliminary costs are
500 — 1000 — 1500 — 2000 — 2250 — 3000.

Div. 1 will feature 5 problems, preliminary costs are 500 — 1000 — 1250 — 2000 — 2500.

Div. 2 will feature 5 problems, preliminary costs are 500 — 1000 — 1500 — 2000 — 2250.

Добрый день!

В воскресенье, 25-го сентября в 14:05 по московскому времени состоится Отборочный Раунд 1 олимпиады для школьников Технокубок 2021. Раунд будет длиться два часа, участникам будут предложены 6 задач. По его результатам лучшие участники (но не более 45% от общего числа участников раунда) будут приглашены на финальный этап в Москву. Для регистрации на раунд и участия перейдите по ссылке. Не забудьте заранее зарегистрироваться на раунд! Для опоздавших будет открыта дополнительная регистрация (с 14:15 до 16:05).

Зарегистрироваться на Отборочный Раунд 1 →
Соревнование открыто для всех в виде отдельных раундов для первого и второго дивизионов.
Для всех участников всех трех редакций этого соревнования будет пересчитан рейтинг.

Параллельно с Отборочным Раундом будут проведены открытые рейтинговые раунды для обоих дивизионов, в них могут принять участие все желающие.

Напомним, что согласно правилам раундов Codeforces во время соревнования ваши решения будут тестироваться только на претестах (предварительном и неполном наборе тестов), а системное тестирование состоится после окончания раунда. Обратите внимание, что претесты не покрывают все возможные случаи входных данных, поэтому тщательно тестируйте свои программы! После прохождения претестов у вас будет возможность заблокировать решение, тем самым получив привилегию искать ошибки и взламывать чужие решения, но отказавшись от возможности перепослать ваше решение при каких-либо обстоятельствах (например, даже если вы найдете ошибку или вас взломают). Со временем задачи падают в стоимости. После системного тестирования учитываются только полные решения. Подробнее про правила соревнований можно прочитать по ссылкам:

• короткое описание формата
• полное описание формата

Регистрация на олимпиаду Технокубок еще открыта. Победителей и призеров олимпиады ждут значительные квоты при поступлении в престижные технические вузы России и ценные призы! Если Вы школьник 8-11 классов и пока не зарегистрировались на Технокубок, то самое время сделать это:

Зарегистрироваться на олимпиаду →
После регистрации на олимпиаду не забудьте зарегистрироваться на Отборочный Раунд!

В финал соревнования будут приглашены лучшие участники каждого из отборочных раундов (но не более 45% от общего числа участников раунда).

Авторы отборочного раунда — AndreySergunin, Endagorion, amethyst0 и я, Golovanov399. Спасибо KAN и 300iq за координацию. Кроме того, хочу выразить благодарность тестерам, без помощи которых этот раунд не состоялся бы: __rkm__, 300iq, arjunsanjeev7, brunomont, Chocobar, iankury, low_, psevdoinsaf, scnucjh и teapotd!

Algorithms Thread Episode 9: Treaps

Good morning everyone!

Episode 9 of AlgorithmsThread comes out shortly after the Div2 round ends. This episode is on Treaps! It covers:

• Fundamentals of Treaps
• Splitting and Merging
• Range reversing

... and more! I also decided to keep up the super-high quality style and made a custom gym set with 5(+2) original problems to make sure you really understand everything that was covered in the lecture. The gym set will be released shortly after the lecture ends, and I hope that the problems will be challenging and fun, even for people who aren't seeing treaps for the first time.

If you have any questions or suggestions, feel free to leave them below. I hope you enjoy the problem statements, and, in the spirit of the upcoming holiday, I'll leave you all with this:

Update: The scoring distribution for this round will be: 1 — 1 — 1 — 1 — (+1) — (+1) — 1

Hi Codeforces!

I am glad to announce and invite you to Codeforces Round #678 (Div. 2), which will be held on Oct/24/2020 17:05 (Moscow time). A couple of weeks ago, we held Codeforces Round #675 (Div. 2) based on the tasks of the Andersen Programming Contest 2020. Qualification, and this time we want to offer you to solve the best 5-6 problems of the finals.

Please note the unusual start time of the round. This round will be rated for the participants with rating lower than 2100.

This is the second year that Andersen has been holding the competition, which is primarily intended to support students of regional Universities in Belarus and Ukraine (starting this year). This year, 60 students from regional universities in Belarus and Ukraine will take part in the finals of the competition.

• The authors of the round are: Aleksey aropan Ropan, Yuri hloya_ygrt Shilyaev, Andrei andrew Mishchanka, Alexander AleXman111 Krivosheev and me.
• The round was coordinated by Nikolay KAN Kalinin and Ildar 300iq Gainullin.
• The round was tested by: Boris ReD_AwHiLe Serenkov, Yahor kefaa2 Dubovik, cckk4467 and rafaelgo2.
• And, of course, thank you very much Mike MikeMirzayanov Mirzayanov for creating the polygon and codeforces platforms.

Thanks a lot for your contribution to the preparation of the round!

Good luck to everyone in the upcoming competition! :)

UPD: The editorial was posted.

Congratulations to the winners of div 2:

1. kuticpcer
2. SevenDawns
3. Its_Gumball
4. iamgqr
5. rishant_m

as well as div 1 winners:

1. jiangly
2. dorijanlendvaj
3. vepifanov
4. krijgertje
5. darkkcyan

Thank you all for participating!

Hello everyone!

Today Codeforces got support for streams! Thanks tourist for the great idea!

There are two popular platforms supported: Twitch and YouTube. The opportunity to add streams to Codeforces is open to red participants and by individual invitations for now. We possibly open this opportunity to more users later.

The idea is that streamers will be able to announce their streams to the Codeforces audience. To do this, you should add the stream to the site using a special section in your profile. Please, note that when adding a Twitch stream, you just need to specify the URL of your channel, and when adding a YouTube broadcast, its unique short link (URL like youtu.be/...)

Shortly before the start of the stream, a notification about the upcoming stream will appear in the sidebar on the right, which will be shown to all site visitors.

For example, right now there is a Errichto's stream announcement in the sidebar.

We have embed stream viewing right into the Codeforces interface. It turned out to be difficult to embed the YouTube stream chat, so there is no such opportunity for now. For Twitch streams, the chat will be visible on Codeforces.

We plan to improve this functionality in the future. What improvements do you think would be reasonable?

Hello! Codeforces Round #677 (Div. 3) will start at Oct/20/2020 17:35 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. 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 (or 8) 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 Daria ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round. Also thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for the discussion of ideas and testing the round!

Good luck!

UPD: Thanks to infinitepro, sladkayaKlubnichka, MrReDoX and Peinot for testing the round and giving the feedback about the problems!

UPD2: Editorial is published!

Hi Codeforces!

stefdasca, koala_bear00 and I are very excited to announce our first contest Codeforces Round #676, which will take place Oct/18/2020 12:05 (Moscow time). The round will be rated for participants with rating up to 2099.

The tasks were written by me with help from stefdasca and koala_bear00 and you have to help some of the authors' favorite musical artists to solve the problems they're faced with.

We hope we compiled a very interesting contest with memorable tasks :)

Special thanks to:

• antontrygubO_o for coordinating our round and pushing us to come up with more and more interesting tasks.

• dorijanlendvaj, kclee2172, Devil, thenymphsofdelphi, jainbot27, Stelutzu, proggerkz, SleepyShashwat, bhaskarjoshi2001, AmShZ, Osama_Alkhodairy, raresdanut, katsurap_, A_N_D_Y, Usu and Miyukine for testing the round and providing useful feedback.

• MikeMirzayanov for awesome Codeforces and Polygon platforms. Thanks!

You will be given 2 hours to solve 5 problems, good luck everyone and have fun!

UPD 1: After the round you can watch videos explaining the solutions to the tasks on stefdasca's Youtube channel.

UPD 2: The round was rescheduled, because of intersection with other scheduled contests.

UPD 3: The scoring distribution is standard 500 — 1000 — 1500 — 2000 — 2500.

UPD 4: The editorial was posted and you can check stefdasca's video solutions aswell.

UPD 5: The round is finished, we are glad everything went smooth and hope you enjoyed our tasks!

Div1 winners (unofficial):

1. I_love_Tanya_Romanova
2. LJC00118
3. kefaa2
4. LayCurse
5. uwi

Div2 winners:

1. RGB_ICPC2
2. _ztyqwq
3. AnakMbah1937
4. SakuraiMomoka
5. asdsasd

Congratulations to those above and to everyone for participating!

Hello, Codeforces!

Welcome to the Codeforces Raif Round 1 (Div. 1 + Div. 2) supported by Raiffeisenbank, that will start on Oct/17/2020 16:05 (Moscow time). It will be a combined rated round for both divisions. Note that the start time is unusual.

All problems were authored and prepared by bensonlzl, oolimry, errorgorn, dvdg6566, shenxy13.

Ari gato to:

• isaf27 and KAN for round coordination and help with preparation

• zhangguangxuan99 for being epic IOI trainer <3

• Our army of testers: Ari, KAN, Monogon, Prabowo, SYY, SleepyShashwat, TeaTime, Tlatoani, _rs_, agul, cstuart, dantoh, jhkoh, kai824, kym2006, lperovskaya, mango_lassi, morzer, postscript, socho, zhangguangxuan99, zscoder for their invaluable advice and suggestions.

• MikeMirzayanov for great systems Codeforces and Polygon.

You will be given 8 problems, one of which would be divided into easy and hard versions, and 150 minutes to solve them.

We hope that statements are short and pretests are strong and that you find the problems interesting! Good luck, have fun and we wish everyone high ratings!

The scoring distribution will be announced closer to the beginning of the round.

Thanks to Raiffeisenbank, winners will get awesome swag:

• 1st-3rd place = Bluetooth speaker

• 4th-10th place = Bumbag

• 11th-20th place = Power Bank

Random 50 participants outside of top-20, who solved at least one problem will receive:

• Thermos Mugs

• Raiffeisenbank t-shirt

About Algorithmic Trading team in Raiffeisenbank

We develop a high-frequency trading (HFT) system for equity, currency and derivative markets. Our business edge is in technology. The main goal is to create a top-notch platform based on fundamental and statistical models and machine learning, with low latency and high throughput. The efficiency and scalability of our code give us a competitive advantage. We are passionate about code quality and strive for highest standards in product development.

If you are interested in internship and employment opportunities in the Raiffeisenbank algo-trading team Capital Markets, or want to get in touch with the bank's recruitment , fill out a form below.

UPD: Scoring distribution: 500 — 1000 — 1000 — 1500 — 1750 — 1750 — (2250+750) — 4000

UPD2: Editorial out!

UPD 3: First ACs and winners

First ACs

A: 300iq

B: icecuber

C: Not-Afraid

D: Radewoosh

E: errichto

F: fmota

G: Radewoosh

H: Radewoosh

Top 5

1. Radewoosh

2. Um_nik

3. kczno1

4. ecnerwala

5. littlelittlehorse

Congratulations to everyone!

Hello Codeforces!

On Oct/11/2020 12:05 (Moscow time) Educational Codeforces Round 96 (Rated for Div. 2) will start. Note that the start time is unusual.

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 extended 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 6 or 7 problems and 2 hours to solve them.

The problems were invented and prepared by Adilbek adedalic Dalabaev, Alex fcspartakm Frolov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

UPD: The editorial is here.

Congratulations to the winners:

Congratulations to the best hackers:

858 successful hacks and 2258 unsuccessful hacks were made in total!

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