Hi. I'm back from USA!

I will do a new lecture tomorrow (Thursday) at 2pm CEST on my Youtube channel: https://www.youtube.com/watch?v=7hFWrKa6yRM. Watch me live (and ask questions), or just watch the video later. This will be part 1, and I will do part 2 in a few days (maybe Tuesday).

UPDATE — part 2 is coming on Thursday, same time. Link: https://www.youtube.com/watch?v=gXxu-Cr4b4c.

There are no prerequisites this time. I recommend reading the materials below in advance, and trying to solve problems 1 and 5. If you are strong, just read problems and see if you can't solve something (maybe problem 8?).

Technique "Exchange Arguments"

If we're given n items and we should choose some of them and choose their order, we should sort them with some strange/tricky comparator, and then do O(N²) dynamic programming. The dp should be dp[pref][used] — best possible result (balance) if we chose used items so far (in the prefix pref).

"Strange/tricky comparator" checks which of the two elements should be earlier, usually just solving the problem for N = 2.

On Nov/28/2018 17:35 (Moscow time) Educational Codeforces Round 55 (Rated for Div. 2) 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 Mike MikeMirzayanov Mirzayanov, Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov and me.

Good luck to all participants!

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

Hello Codeforces!

We are excited to announce that the Hello Muscat Programming Bootcamp registration is open! The camp will take place from March 9th to March 15th, 2019, and our early bird discount of 15% is going until December 15th!

This next edition in our Hello Programming Bootcamp will run in parallel with the traditional Moscow ICPC Workshop — both Bootcamps’ contests will be identical, and contestants will be able to see their position in the General Leaderboard. Every day, both camps will be competing simultaneously, 4,000 kilometers from each other!

We would also like to remind you that the deadline for applying to the Master’s in Robotics programme scholarship will close November 30th, so we encourage you to check out the website to see the all the requirements and apply!

UPD: You can discuss the problems after the contest at a local Discord server.

UPD2:

Congratulations to the winners:

Congratulations to the best hackers:

1354 successful hacks and 1065 unsuccessful hacks were made in total!

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

UPD3: Editorial is out

Hello!

This weekend we would like to share an online-mirror of 2018-2019 ACM-ICPC, Asia Xuzhou Regional Contest with you. Please notice its start time is Saturday, December 1, 2018 at 18:00 (UTC+8) and we will be there for answering your questions. You are able to register 6 hours before the contest starts. However, before the registration starts, you may not view this contest on Gym. After the online-mirror contest, you can virtually participate at any time you want.

The 2018 ACM-ICPC Asia Xuzhou Regional Contest has been finished at China University of Mining and Technology, on October 28. Although 288 teams participated in the onsite contest, only 195 of them (including invited teams) finally solved at least one of 13 problems in 5 hours. Is the contest too hard? Or is the difficulty only applied to Chinese participants? We cannot get a conclusion clearly... Anyway, we hope these problems will benefit people who want to gain great results in ICPC.

The problems are prepared by AHdoc, Claris, quailty and me. Thanks to niike0goood and zscc for discussing ideas, yefllower and niike0goood for testing, Syloviaely for playing a crucial role in the contest, and MikeMirzayanov for developing Codeforces and Polygon.

Also, as a kindly reminder, Jisuanke will hold another online-mirror contest that will start on Sunday, December 2, 2018 at 12:00 (UTC+8).

We kindly ask everybody who has already read the problems not to participate this online-mirror contest or discuss any solution in public before the contest has ended. Your cooperation will be greatly appreciated.

UPD1: Registration starts. You may view this page to register.

Hi!

Tomorrow, at Nov/25/2018 19:35 (Moscow time) we will host the final round of Mail.Ru Cup 2018. The problems were authored and prepared by Codeforces team: me, Dmitry cdkrot Sayutin, Ildar 300iq Gainullin and Mike MikeMirzayanov Mirzayanov, and also Maxim Neon Mezhcheryakov. Huge thanks to Grigory vintage_Vlad_Makeev Reznikov abd Kamil Errichto Debowski for problems' testing!

This round is the final in the new championship called Mail.Ru Cup, you can learn more about it following the link. The round will be rated for everybody!

After the round we will know who will get the following prizes:

• First place — Apple MacBook Air
• Second and third place — Apple iPad
• Fourth, fifth, sixth places — Samsung Gear S3
• Traditionally, the top 100 championship participants will get cool T-shirts!

In each round, top 100 participants get prize points according to the table. The championship's result of a participant is the sum of the two largest results he gets on the three rounds. The results of the two first rounds are published here. In case of ties in the top six places, they will be broken by the sum of in-round scores in the corresponding (best for the participant) two rounds.

There will be eight problems and two and a half hours to solve them.

Good luck!

P. S. MikeMirzayanov invites everybody to the official Codeforces channel in Telegram: t.me/codeforces_official.

The round has finished, thanks everybody, hope you liked the problems!

Congratolations to the winners of the third round of Mail.Ru Cup 2018:

1. Radewoosh
2. V--o_o--V
3. ch_egor
4. ksun48
5. RAVEman

The results of the Cup will be announced shortly.

The editorial is here.

Hi, Codeforces!

Codeforces Round #524 (Div. 2) will be held on Nov/24/2018 10:35 (Moscow time). The round will be rated for the second division (rating is less than 2100). As usual, participants from the first division will be able to participate out of competition.

You will be given 6 problems and 2 hours and 15 minutes to solve them.

This round was prepared by me, arsijo, and stanislav.bezkorovainyi.

Thanks to Markellonchik, iSlava, and Barichek for testing, Jajceslav for pictures to the problems, and MikeMirzayanov for wonderful platforms Codeforces and Polygon.

The round is based on the II stage of Ukrainian Olympiad in Informatics, that is why please do not discuss the problems before the system testing start.

UPD: Scoring distribution: 500 — 750 — 1250 — 1750 — 2250 — 2500.

UPD2: Congratulations to the winners:

1. Qingzhi_chan
2. Laggay
3. H-C-H
4. lqs2015
5. Trrui

UPD3: Editorial.

Hello.

As I wrote into a comment, last round we are faced with a strong DDOS-attack which ruined the competition. I don't know who did it, I also don't know reasons to do it. I'm very upset about the situation and ready to make an effort to be prepared for such issues.

I spend a lot of time to be ready for such incidents.

Here are steps you need to do to be ready for unexpected failures:

• Join our telegram channel by the link https://t.me/codeforces_official to read urgent news.
• Be sure that you know the password of your Codeforces account. If you don't remember it, just use the password recovery feature. Please, do it right now.
• I've implemented a minimalistic website for replacing the main site in case of emergencies. Now you can only read problems, view your submissions (without any details), submit codes. Probably, later I'll add some more features, but anyway, the minimalistic version will have only vital features to take part in a contest. I've deployed it in several places, you can visit any of them by the links: http://m1.codeforces.com, http://m2.codeforces.com, http://m3.codeforces.com. If any of them is unavailable, just use another. Do not use them if the main website is alive.

UPD: Now you can enter minimalistic websites without a password. In this case, an email with a secret enter link will be sent to you.

Hi everyone!

I would like to invite you to my second Codeforces Round, which I have made with my friend and Snackdown partner Jeel_Vaishnav.

With that said, I bring to your attention our new Codeforces Round 523 (Div. 2) that will take place on Nov/22/2018 18:45 (Moscow time). If your rating is less than 2100, this round will be rated for you; otherwise, you can participate out of competition.

I would really like to thank Jeel_Vaishnav for his help with preparing problems, cdkrot for coordinating our round and Um_nik, vintage_Vlad_Makeev, Aleks5d, KeyurJain & Mahir83 for testing the problems. I would also like to thank MikeMirzayanov for Codeforces and Polygon platforms.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

Link to My Coding Library for those interested :)

Good luck! :D

UPD: Scoring Distribution: 500-1000-1500-2000-2500-2750

UPD2: Editorial

Hello, Codeforces!

We are pleased to announce the 1st "Hello Muscat!" ICPC Programming Bootcamp, organised by Harbour.Space University with Moscow Workshops ICPC in collaboration with Moscow Institute of Physics and Technology, ITMO University, Saint Petersburg State University, GUTech University, and of course Codeforces! The Bootcamp's Gold Sponsor is Phaze Ventures, a venture capital firm and innovation platform based in Oman. The Bootcamp’s General Partner is Sberbank, the largest Russian bank and leading innovator.

We are inviting all of you to join us during 9 — 15 March, 2019 in Muscat, the capital of Oman, for an intense 7 days of programming! As always, we can't wait to see all of you learn, practice and compete on the international stage, smoothing your road towards the April World Finals in Porto.

How it works: "Hello Muscat!" Programming Bootcamp will run in parallel with the traditional Moscow pre-Finals ICPC Workshop — both Bootcamps' contests will be identical, and contestants will be able to see their position in the General Leaderboard. Every day, both camps will be competing simultaneously, 5,500 kilometers from each other!

Michael Endagorion Tikhomirov will be the Head of Programming Committee for both Muscat and Moscow. The Chief Judge of both camps will be Oleg snarknews Khristenko, and the General Coordinator is Alexey Maleev, the founder of Moscow Workshops ICPC.

All participants will have the opportunity to work under some of the most recognized coaches in the industry: Mike MikeMirzayanov Mirzayanov, Andrew andrewzta Stankevich, Michael Endagorion Tikhomirov, Gleb GlebsHP Evstropov, Artem VArtem Vasilyev, Ivan ifsmirnov Smirnov, Ilya izban Zban, and other world renowned Russian coaches. It will be an important opportunity for teams from all over the world to learn from these well-known and successful coaches in the ICPC world.

You can leave your contact details or register here — you'll be contacted upon registration.

GUtech Campus in Muscat, Oman

The campus is a first-of-its-kind project, and establishes Omani architecture at an international level.

The boot camp in Oman will be available to teams of different skill levels – separated by two divisions of difficulty:

• Division A. Designed to prepare students to excel and win medals in the next ICPC World Finals.
• Division B. Designed to help teams prepare for the next season of ICPC Regionals and international competitions. This is an appropriate introduction for teams and students without extensive experience in the world of ICPC and competitive programming competitions in general. The Division B curriculum features thematic lectures and contests.

The participation fee is unchanged: €1270 per person (cultural programme, accommodation and half-board meals included). Single participants and teams must register before 15 December to receive the 15% off Early Bird Discount, or the 20% off Loyalty Discount, which is awarded to teams that participated in previous Hello Programming Bootcamps or Moscow Workshops ICPC Bootcamps.

The final registration deadline is February 25, 2019.

You can ask any questions by email: [email protected]

Harbour.Space University and Moscow Workshops ICPC collective efforts have resulted in a series of successful programming Hello Bootcamps, which continue to expand across the globe. In order to experience the atmosphere of the events, we suggest you familiarise yourself with the photos and videos from the previous Hello Programming Bootcamps.

Here's a quick recap of the latest 3rd Hello Barcelona ICPC Programming Bootcamp.

Can't download http://assets.codeforces.com/photos/oman_post_2018/list.txt [tried twice].

Hi all!

This weekend, at Nov/18/2018 19:05 (Moscow time) we will hold Codeforces Round 522. It is based on problems of Technocup 2019 Elimination Round 3 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 2019 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 round was prepared by Alexander Golovanov399 Golovanov, Evgeny WHITE2302 Belyh, Alexandra demon1999 Drozdova, Arsenii craborac Kirillov, Ivan ifsmirnov Smirnov, Artem komendart Komendantian, Roman Roms Glazov, Daria Dashk0 Kolodzey and me.

Huge thanks to Grigoty vintage_Vlad_Makeev Reznikov, Ildar 300iq Gainullin, Ilia irkstepanov Stepanov, Andrey AndreySergunin Sergunin for testing.

Have fun!

The round is over, we apologize for the issues with platform accessibility. The round is declared unrated.

Congratulations to the winners!

Technocup 2019 - Elimination Round 3

1. 998kover
2. Kuyan
3. paradox
4. ANTIMIRAGE
5. YaKon4ick

Codeforces Round 522 (Div. 1, based on Technocup 2019 Elimination Round 3)

1. ksun48
2. Anadi
3. LHiC
4. Um_nik
5. mnbvmar

Codeforces Round 522 (Div. 2, based on Technocup 2019 Elimination Round 3)

1. liriKl
2. Moysenko
3. okwedook
4. fauzdar65
5. Bismarck

Thank you all for joining!

The editorial is published.