Hello Codeforces!

On June 29, 18:05 MSK Educational Codeforces Round 24 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.

The round will be unrated for all users and will be held on extented ACM ICPC rules. After the end of the contest you will have one day 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 15 minutes to solve them.

The problems were prepared by Mikhail PikMike Piklyaev, Alexey Perforator Ripinen and me.

Good luck to all participants!

I also have a message from Harbour.Space University about the ML course held at the university:

Nowadays machine learning technologies are widely used in practice in various applied fields such as retail, mass media, PR and marketing, banking, telecommunications, manufacturing, science and many other areas.

We are pleased to announce our Industrial Machine Learning course, aimed to teach the structure and the life cycle of the machine learning process and covers topics ranging from the problem statement to final quality assessment as well as estimation of the economic effect.

This course is taught by two Data Scientists from Yandex, Emeli Dral and Victor Kantor. Emeli Dral is the Head of Predictive Analysis, whereas Victor Kantor is the Head of User Behaviour Analysis Group at Yandex.

http://in.harbour.space/data-science/industrial-machine-learning/

They share with us their knowledge on everything from the most promising applications of data science today to applying the latest advancements in machine learning to your work.

During the discussion after the Round 421 it turned out that the author's solution was wrong. Yes, we had several testers, we had a bruteforce solution that worked correctly, we had a stress testing between the bruteforce and the main solutions. However, all these measures haven't prevented the mistake: the testers haven't noted the issue, the stress haven't found any counter-tests. The solutions also produced the same answers all small tests we had in the testset, so we only found the issue when a test used for a hack was added.

We are terribly sorry about the mistake. We did our best to ensure the problems are ok, I don't know any available method that we haven't used to check the problem.

We've spent the last few hours trying to come up with a new, correct solution to the problem, but right now I don't see any solution that seems undoubtedly correct to me. There are a few that work better than the author's, but yet unproved, you can try to prove this one, for example. I think this problem should be solvable with careful case analysis, and I'm trying to do this right now. I'll post the results here. I'd also be glad if someone post the solution with proof.

Thus, I apologize that the round should be declared unrated. Hope for your understanding.

Hello, Codeforces!

I'd like to invite you to Codeforces Round #421 that will be held at June 27th, 2017 at 17:35 MSK.

Yes, it's my first round, and yes, it's another round from purple.

Great thanks to KAN for help in preparation of this round, dans for help on first stages and testing, Belonogov, white2302, hloya_ygrt, Perforator for testing the problems, and MikeMirzayanov for great systems Codeforces and Polygon.

As always, participants of both divisions will be given 5 problems and 2 hours to solve them. Scoring will be announced before the round.

Good Luck and Have Fun!

UPD1: Scoring is standart for both divisions: 500-1000-1500-2000-2500

We are working on the issue with problem A in div. 1. We will announce the decision later.

Due to the issue with problem A, the round is declared unrated. More details.

Nevermind all promblems, Editorial must be, so it's here.

Hi everyone!

It's the round you've been waiting for... Codeforces Round #420 (Div 2). It will take place tomorrow, 25 June 2017, at 17:35 MSK. As always, Div. 1 participants are encouraged to join out of competition. The round will be rated for Div. 2 participants and will have 5 problems to be completed in 2 hours.

I wouldn't be able to create this round without the help of many people: KAN for lots of help in preparing the contest, gainullin.ildar and Alladdin for testing and providing feedback, and as always MikeMirzayanov for the Codeforces and Polygon platforms.

This will be my second contest, and I'm glad to get such a nice round number :). Hopefully, you'll find the problems interesting. Of course, you should read all the problems so you can solve problems you find easy or interesting.

To excite some and disappoint others, the round theme will have nothing to do with the number 420. Instead, continuing the anime themes of the last two rounds, round #420 will feature mad scientist Rintaro Okabe (don't read spoilers!) from the anime Steins;Gate. Statements will not contain any spoilers, but you might find the problems slightly more amusing if you've watched the series. Of course, you should watch the series if you havent :)!

As per Codeforces tradition, scoring distribution will be announced shortly before the contest. Good luck, and I hope you can help Okabe with all 5 tasks :D!

Scoring is standard: 500-1000-1500-2000-2500!

Update: Sorry for delays.

Update: Editorial is here: http://codeforces.com/blog/entry/52895

I really apologize for the issues during the round. It's upset a lot of people and I should have taken more care. Hopefully you won't hold this against Okabe or Steins;Gate anime :P

Here are the contest winners! Congratulations!

Div. 1

1. nuip
2. uwi
3. sugim48
4. xumingkuan
5. HellKitsune

Div. 2

1. Parachutes
2. Possessed_by_Phoenix
3. visitWorld
4. y553546436
5. a_student_follower

Thanks for participation everyone! Hope to write more problems in the future (without bugs)!

Mabuhay!

I am honored to announce Codeforces Round #419. It will take place tomorrow, on June 17, 17:35 MSK.

The problems in this round are written by me, robinyu. I believe it is the first Codeforces round with a Philippine writer. I would like to extend my heartfelt gratitude to kevinsogo, AlexFetisov and winger for their invaluable help in testing the problems, KAN for his endless patience and support in preparing the contest, and of course MikeMirzayanov for the absolutely amazing Codeforces and Polygon platforms.

In this round, you will be helping Karen in her day-to-day routine.

There will be pretty pictures, drawn by the lovely Kazenokaze. Do not miss the round!

Both divisions will be given five problems and will have two hours to solve them. Keeping with authentic Codeforces tradition, scoring will be announced right before the round.

As a matter of course, you are highly recommended to read all the problems; though problems are arranged by expected difficulty, you may find some problems easier than others.

I hope you will enjoy the problems as much as I did writing them!

The scoring for this round is:

Div. 1: 500 — 1250 — 1500 — 2250 — 2250
Div. 2: 500 — 1000 — 1500 — 2000 — 2750

Good luck, and I wish you all high ratings and bug-free code!

Update: Congratulations to all winners!

Special congratulations to Radewoosh for his second consecutive Div. 1 round victory, and to both him and yutaka1999 for solving all tasks!

Thanks for your patience. The editorial has been posted. Hope it was worth the wait!

Hello Codeforces!

On June 15, 18:05 MSK Educational Codeforces Round 23 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.

The round will be unrated for all users and will be held on extented ACM ICPC rules. After the end of the contest you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

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

The problems were prepared by Mikhail PikMike Piklyaev, Vladimir 0n25 Petrov and me. Huge thanks to Alexey Perforator Ripinen, Alexey ashmelev Shmelev and Maxim HellKitsune Finutin for testing!

Good luck to all participants!

UPD. I am pleased to announce the 2nd Hello Barcelona Programming Bootcamp in collaboration with Moscow Workshops ACM ICPC, which will be hosted by our partner Harbour.Space University together with Moscow Workshops ACM ICPC, ITMO University, Moscow Physics and Technology University, Saint Petersburg State University and Codeforces!

LEARN MORE

UPD: The editorial is published.

Hello, Codeforces!

I am pleased to announce the 2nd Hello Barcelona Programming Bootcamp in collaboration with Moscow Workshops ACM ICPC, which will be hosted by our partner Harbour.Space University together with Moscow Workshops ACM ICPC, ITMO University, Moscow Physics and Technology University, Saint Petersburg State University and Codeforces!

The boot camp will be held from September 27th to October 5th in Barcelona. This time it will be at the beautiful and technologically mind-bending Media-TIC building — the Smart Building of Tomorrow.

Media-TIC building — the Smart Building of Tomorrow

The world's greatest coaches will be attending: Andrew andrewzta Stankevich, Michael Endagorion Tikhomirov, Gleb GlebsHP Evstropov, Artem VArtem Vasilyev and other world renowned Russian coaches. As a coach, I will come too. The Chief Judge of the camp is Oleg snarknews Khristenko. Seriously, it will be a unique opportunity for teams around the world to learn from such well-known and successful coaches in the ACM-ICPC world.

Having visited the first Hello Barcelona programming Bootcamp in February, I left the event feeling inspired from the overall atmosphere. I am sure that all teams received an immense amount of knowledge and skills. As one of the coaches, all of the flattering reviews about the camp from the participants were pleasant for me to hear. I am very glad that these camps are becoming regular. Harbour.Space University and Moscow Workshops ACM ICPC have done a job worthy of admiration!

The Bootcamp will be split in two divisions:

• Division A. Designed to prepare students to excel and win medals in the next ACM-ICPC World Finals.

• Division B. Designed to help teams prepare for the next season of ACM-ICPC Regionals and international competitions. This is an appropriate introduction for teams and students new to the world of ACM 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 program, accommodation and half-board meals included).

Single participants and teams must register by July 1st, 2017 to receive the 15% off-Early Bird Discount, or the 20% off-Loyalty Discount, which is awarded to teams that participated in previous Moscow Workshops ACM ICPC boot camps.

You can ask any questions by email: hello@harbour.space

Hope to meet you on the Bootcamp, Mike Mirzayanov

In order to experience the atmosphere of the event, I suggest you familiarize yourself with the photos and videos from the 1st Hello Barcelona programming Bootcamp in collaboration with Moscow Workshops ACM ICPC.

418 I'm a teapot

Hi everyone! >///<

I'd like to invite you to Codeforces Round #418 which begins at 15:05 MSK on 7 June. Please note that the timing is unusual.

This is my first round here! KAN reviewed the contest and helped me through the preparation process, while Alladdin, neckbosov and Tommyr7 tested all the problems, and MikeMirzayanov and the awesome Codeforces and Polygon platforms made all this happen miraculously. This wouldn't have been possible without your efforts!

The round is rated for the second division, and participants from the first division can take part out of competition. As usual, there are five problems and two hours to solve them. The problems will feature... Well, let's wait and see :)

The scoring distribution will be announced later.

Hope everyone few bugs and fair ratings. Looking forward to seeing you then!

UPD 1 Scoring will be 500-1000-1750-1750-2500. It's recommended to read all problems' statements so as to find the problems that suit you — we tried quite hard to make them clear and interesting.

UPD 2 The round is delayed for 10 minutes due to technical issues. Apologies.

UPD 3 System test is done. Congratulations to the winners!

Div. 2 Top 5

1. memanon
2. marmoset
3. liu_runda
4. yieldar
5. krydom

Overall Top 5

1. xumingkuan
2. HellKitsune
3. natsugiri
4. MakeYanGreatAgain
5. irkstepanov

Hope you all enjoyed the contest. You all did a great job! The editorial is on the way, please be patient :)

UPD 4 For the impatient, here are the tutorials for problems A to C. More are coming!

UPD 5 The complete editorial is out. Cheers!