Good day to you, Codeforces!

Let me introduce you Codeforces Round #539, that will take place at Saturday, February 16, 2019 at 19:35. The round will be rated for both divisions.

The problems of this round were developed by markysha, xolm, aleex. That is our first round on Codeforces, and I hope not the last one :)

Thanks everyone who helped with tasks preparation:

• Our coordinator arsijo for his help with everything
• Thanks very much kefaa2, GandalfTheGrey, sharepoLOVEDDD, austrian_artist, Adalbert, StasyaCat, Fekete and Daryusz for testing this round (yeah, we approached testing thoroughly :))
• gepardo for playing a crutial role in the contest (what? you'll see)
• And of course MikeMirzayanov for Polygon and Codeforces.

There will be 6 tasks and 2 hours 30 minutes to solve them. As usual, the score distribution will be revealed shortly before the contest.

Wish you quick ideas and short solutions!

Upd.
Div. 1: 500 — 1250 — 1750 — 1750 — 2250 — 3000
Div. 2: 500 — 1000 — 1500 — 2250 — 2750 — 2750

TREMBLE BEFORE THE MIGHTY OMEGALULGRAPE

Hello Codeforces!

We are honored to invite you to Codeforces Round #538 (Div. 2), which will take place at Feb/10/2019 17:05 (Moscow time). The round will be rated for all Division 2 participants (with rating less than 2100). Still, we warmly welcome Division 1 participants to join us out of competition.

You will be given 6 problems to solve in 2 hours. The round's problems were initially prepared by Duy-Bach Akikaze Le, Xuan-Tung neko_nyaa Nguyen and Xuan-Quang xuanquang1999 D. Nguyen.

There will be an interactive problem in this round. Learn more about interactive problems here.

This is our first attempt in making a Codeforces round, so suggestions are much welcome to help us improve ourselves. ;)

We also want to thanks many friends for making this round possible:

• Dmitry _kun_ Sayutin for coordinating the round, providing a neat idea on one problem and some Russian translations.
• Andrew GreenGrape Rayskiy for various suggestions on the problems, some other Russian translations, and most importantly, peacefully submitted himself to be quarantined from pretests. ;)
• Michal majk Svagerka for testing the round.
• And last but not least, Mike MikeMirzayanov Mirzayanov for the amazing Codeforces and Polygon platform, without which this round would never be possible :D

P/s: I will be at the Discord CP Community to discuss the problems after the coding phase. However, please follow the rules and don't discuss the problems during the contest by any means.

Wish everyone good luck and high rating!

UPD1: Score distribution: 500-1250-1500-2000-2000-2750

UPD2: Editorial is published.

UPD3: The contest is finished. I apologized for the "somewhat" weak pretests at here and there. Anyway, time to celebrate our winners ;)

Official participants:

1. xlk200
2. vasilescu_mihai
3. Cinro_9baka
4. africamonkey
5. 2019_BecameMaster
6. cdsfcesf
7. yww_AFO
8. hr_tian_xia_di_2
9. JZmster
10. chinmay0906

Div.1 + Div.2 participants:

1. Hazyknight
2. tfg
3. tempura0224
4. xlk200
5. sava-cska
6. mango_lassi
7. I_love_Tanya_Romanova
8. ec24
9. vasilescu_mihai
10. Cinro_9baka

Hi!

Tomorrow, at Feb/07/2019 16:35 (Moscow time) we will host Codeforces Global Round 1.

It is the first round of a new 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 2019:

• 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 a team of authors: aitch, simonlindholm, grphil, V--gLaSsH0ldEr593--V, GreenGrape, Nebuchadnezzar, _kun_ and me. Thanks arsijo and _kun_ for their help in the round's coordination, and also majk, pashka, Jeel_Vaishnav, Ashishgup and UnstoppableSolveMachine for testing the round!

Good luck!

Congratulations to the winners!

1. tourist
2. Um_nik
3. TLE
4. mnbvmar
5. sunset
6. wxhtxdy
7. ksun48
8. cki86201
9. snuke
10. fateice

Editorial.

Microsoft’s Quantum team is excited to announce the Q# Coding Contest – Winter 2019! In this contest you can put your quantum programming skills to the test, solving quantum computing tasks in Q#. Winners will receive a Microsoft Quantum T-shirt!

Quantum computing is a radically different computing paradigm compared to classical computing. Indeed, it is so different that some tasks that are believed to be classically intractable (such as factoring integers or simulating physical systems) can be performed efficiently on a quantum computer. In 2017 Microsoft introduced the Quantum Development Kit which includes the Q# programming language. Q# can be used with Visual Studio, Visual Studio Code or the command line, on Windows, macOS, and Linux.

In summer of 2018 we hosted the first quantum programming contest, which included problems on introductory topics in quantum computing: superposition, measurement, quantum oracles and simple algorithms. This contest will offer harder problems on some of these topics as well as introduce some new topics.

The contest will run from March 1 to March 4. The rules of the contest are:

• The contest will have 12 tasks of various complexity levels.
• To solve each task, you will write Q# code to implement the described transformation on the given set of qubits or to perform a more challenging task. Solutions are accepted in Q# only.
• The solution is correct if it passes all tests from a predefined test set. You will know whether the solution is correct soon after submitting it.
• Participants are ranked according to the number of correctly solved tasks.
• Ties are resolved based on lowest penalty time for all tasks, which is computed as the latest submission time (the time since the start of the contest) for any of the correctly solved tasks. An extra penalty of 20 minutes is added for each failed submission on solved tasks (i.e., if you never solve the task, you will not be penalized for trying that task).
• The top 50 ranked participants will receive a Microsoft Quantum T-shirt.
• NO PURCHASE NECESSARY. Must be 16 years of age or older. Game ends 3/4/19. For details, see Official Rules.

We will offer a warmup round the weekend before the contest, from February 22 to February 25. Participation in the warmup round is entirely optional. The warmup round includes simpler tasks on the topics covered in the main contest and gives you an opportunity to get familiar with the contest environment and submission system beforehand, as well as refresh or learn the basics of quantum computing and the Q# programming language. During the warmup round everybody is encouraged to discuss the tasks and the solutions. Once the warmup round is over, we will publish the editorials explaining both the quantum computing logic behind the solution and the Q# implementation on the contest page.

Another great way to prepare for the contest is to solve some of the Quantum Katas. They offer problems on a variety of quantum programming topics, and they are very similar to the ones used in the contest. In fact, the participants of the summer Q# contest will recognize the contest problems in some of the kata tasks :-)

Good luck! We hope you enjoy the contest!

For first time Codeforces users:

1. Create user account here.
2. Register for the warmup round here.
3. Register for the contest here.
4. Once the warmup round starts on February 22, access the problems here.
5. Once the contest starts on March 1, access the problems here.

Quantum computing and Q# materials:

• Quantum Computing: Lecture Notes by Ronald de Wolf.
• A collection of awesome quantum computing learning resources, including MOOCs and books.
• Q# installation instructions and documentation.
• Quantum Katas — Q# programming exercises.
• Q# Language Quick Reference.

Note that this contest will use Q# 0.4, while the previous contest used Q# 0.2. A lot of code written in 0.2 will still work in 0.4; for details on breaking changes and new features please see release notes.

Hi Codeforces!

February 2019 is already on the calendar, which means that I was late with the report for 2018. Better late than never! Let's remember last year.

In 2018, _kun_, 300iq and arsijo joined the team of coordinators. The work of the coordinators is headed (and is the coordinator of the coordinators) KAN. I really hope that a more measured schedule of preparing rounds by a large team of coordinators will give a better insight into the contests. The main innovations in the platform are implemented by me and the developers kuviman, fcspartakm, MaximShipko. Great work on the organization of events and prizes mailing was done by gKseni.

Special thanks to the writers of the problems and testers. It is your content that charges the community with life and unites all of us. Thank you for the problems!

And now let's summarize the 2018th year.

Partner Events

We are pleased to hold programming competitions with companies or for companies. I'm sure this is a great way to support the community of young programmers and hire talented candidates. Here is a list of our main partners this year:

• Telegram and personally Pavel Durov is supporting Codeforces activities for many years, every regular round is held with their help, thank you!
• VK, VK Cup — team competition for young Russian-speaking programmers with a series of elimination rounds and finals in St. Petersburg
• Mail.Ru, Mail.Ru Cup — open individual programming competition, consists of several stages, Technocup — open competition for schoolchildren
• Harbour.Space University — a series of educational rounds, the selection of summer school Tech Scouts
• Lyft — a two-level competition with the Final at Lyft headquarters (California) and the mirror contest for worldwide participants
• Avito, Avito Code Challenge and Avito Cool Challenge — open partnership rounds targeting a wide international audience
• Microsoft, Microsoft Q # Coding Contest — unusual quantum computing competition
• AIM Tech — open partnership round targeting a wide international audience
• Huawei — research competition (marathon) with elements of machine learning
• IQ Option — private round as a corporate training

Hello!

It is always satisfying and important for me when former contest participants offer their help to the community and support the development of programming competitions. And now I am in a hurry to share the news that thanks to the support of XTX Markets and the personal participation of Yuri Bedny and Alexander Gerko, we are launching a new line of Codeforces Global Rounds. Hooray!

Like many of you, I had never heard of XTX Markets before but it is one of the largest quantitative-driven electronic liquidity providers in the world. I understand little about the financial sector, but with their 34,148 cores and 42 petabytes of usable storage in their research cluster, XTX’s rapid growth and strong market share globally speak for themselves.

So, in 2019, with the support of XTX Markets, 6 rounds of the new Codeforces Global Rounds will be held. These will be common rounds for both divisions of 7–9 problems each. The duration of the rounds will be 2-3 hours, depending on the number and complexity of the problems. All such rounds will be rated for all participants. At each such round, 50 brand T-shirts will be handed out, and we will be happy to give T-shirts to all authors and problem testers.

I will be very happy for Codeforces to work with the best authors of the problems. I hope that the XTX Markets initiative will allow for interesting and testing rounds that will delight community members! We have the opportunity to pay $800, double fee, for the preparation of a full set of problems (for some rounds we may collect problems from different authors).

The first Global Round will take place very soon — starting Feb/07/2019 16:35 (Moscow time). I hope you will enjoy the round!

— MikeMirzayanov

Hello Everyone!

I would like to invite you to CodeCraft-19, which is a part of Felicity, the annual techno-cultural fest of IIIT Hyderabad. It will take place on Feb/03/2019 18:35 (Moscow time).

The round will be rated for Div 2 participants (whose ratings are lower than 2100). As usual, participants from the first division can participate in the contest out of the competition. You will be given 5 problems, all of which are based on the theme of our fest, "Superheroes".

I would like to thank the CodeCraft team -- nir123, additya1998, devanshg27, gaurav172, night_fury208, shaanknight, psaini, sharmaritvik60, swetanjal and vivace_jr -- for helping in preparation of the problemset. I would also like to thank KAN and 300iq for round coordination, osaaateiasavtnl., Aleks5d and mohammedehab2002 for testing the round and MikeMirzayanov for the great Codeforces and Polygon platforms.

Following the convention, score distribution will be announced shortly before the contest.

Good luck to all the participants!

UPD1: 500-1000-1500-2000-2500

UPD2 Editorial is published! We sincerely apologize for the weak pretests in B and for the difficulty gap from C to D which turned out to be harder than what we expected.

UPD3 Congratulations to the winners!

1. prodakcin

2. fastfurioustransform

3. yww_AFO

4. Mindstorm

5. ThankGodItsFriday

6. Issh

7. hfctf0210

8. Y.nnnnnnn

9. Choopa_choops

10. EtherLand

Hello, Codeforces!

It's my honor to invite you to Codeforces Round #536 (Div. 2), which takes place at 12:35 UTC, January 31st, 2019. The round will be rated for all division 2 participants (with rating less than 2100). Also we warmly welcome those division 1 participants to join us out of competition.

This is my second round on Codeforces platform, and my first round was on January 31st, 2018, which is such a coincidence that I would like to say thanks to KAN for his awesome coordination and great dedication to this round. Besides, much thanks to testers Aleks5d, cyand1317, mohammedehab2002, osaaateiasavtnl. for their excellent testing work. Also, I would like to appreciate the Codeforces platform created and maintained by MikeMirzayanov, without which the round wouldn't be possible.

In order to celebrate the Lunar New Year (or Spring Festival) originated in China on February 5th, I proposed the round with 6 problems, whose theme is about the Lunar New Year. In this round, you are going to help Alice and Bob to solve some problems in the preparation of celebrating the Lunar New Year in 2 hours. I hope that those problems can interest you and improve your programming abilities, at the same time, bring you luckiness as well as high rating in the coming Lunar New Year!

As a convention, the scoring distribution will be announced soon.

Again, wish you more luckiness and higher rating!

UPD1: Editorial is published.

UPD2: The scoring distribution will be 500-1000-1250-1500-2250-3000. Note that there are 6 problems and you will be given 2 hours to solve them.

UPD3: System test is finished. We are sorry for that technical issue which ruined your happiness. Despite the issue, I hope you do learn something from the problem set, which might be far more important than the rating itself. Enjoy problems, and looking forward to the next contest with better problem set to learn something new, which in my opinion is what Codeforces platform wants to provide us with. Thanks for your participation and dedication even after the unrated announcement. :)

UPD4: The real Editorial is published. Thanks for your patience.

UPD5: Despite that the round is unrated, I have to announce the winners, who deserve it because of their hard work.

Div. 2

1. ksi1996

2. newbieyzr

3. Zharaskhan

4. I_AM_CHTHOLLY

5. mzhmxzh

6. radoslav192

7. Vit.C

8. visitWorld

9. yycdage

10. xuzhiyuan

11. zhangqingqi

12. Crossguard

13. gtrhetr

14. Itst

15. HwSh