Hello Codeforces!

On Apr/10/2020 17:35 (Moscow time) Educational Codeforces Round 85 (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 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 Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Ne0n25 Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

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

Hey Codeforces,

What a crazy month it’s been!

We hope you and your loved ones are taking care of one another and catching up on everything you didn’t have time for on your normal schedules.

We’ve temporarily closed our physical campus and moved our classes online. It’s not as bad as it sounds though — we’ve always known the future is digital, so we were already preparing for this moment. Either way, we’re back.

SPECIAL PRIZE FOR EDU ROUND 85

This digital transformation opens the door to some pretty awesome new opportunities that allow us to get closer to our community, no matter where in the world they are.

That’s why we have a special prize for the next Educational Round, a space in a course of your choice from our Computer Science or Data Science Programs. You’ll be able to study online with us for 1, 2 or 3 weeks under some of the best Data and Computer Scientists in the world, with all fees on us.

The prize will be for the top 3 users who have confirmed their desire to participate in this competition. To sign up for it, leave us your handle in the form below.

Enrollment in the course you will participate in will depend upon the availability of the course, as well as the prerequisites required for that course.

We hope this provides you with extra incentive for the round, and we’re looking forward to seeing some of you soon!

FULL SCHOLARSHIPS FOR BACHELOR’S PROGRAM

On a different note, we’re happy to announce that we’re offering full scholarships for the most talented high school students who want to study in our Computer Science or Data Science Bachelor’s programs at our university.

At the moment, we have two types of scholarships available:

The Full Scholarship. For the best of the best — all tuition costs are covered by the university. Just show up and show us what you’ve got.

The Co-Creator Scholarship. For those who want to help us change education — all tuition costs are covered by the university, and in addition to your studies, you get to help the Harbour.Space team on their mission for 4 hours/day, getting valuable practical experience in the field and working in a team with some of the brightest young professionals in town.

Fill out the form below and we will contact you for the next steps!

Looking forward to seeing you kick some ass in the next Educational Round, and stay safe!

Best, Harbour.Space University

내가 돌아왔다! (Hello, Codeforces!)

I am thrilled to introduce you to Codeforces Round #633. Following are basic information:

• This contest will take place on Apr/12/2020 17:05 (Moscow time).
• The round is rated for all participants who can understand this announcement. There will be two divisions.
• There are 5 problems in each division and you will have 2 hours to solve it.
• Score distribution will be announced later.

Followings are contributors:

• Authors: McDic — All Div.2 problems and Div1D, tzuyu_chou — Div1E
• Coordinator: antontrygubO_o
• Testers:
  • Phase 1 (When this round was supposed to be Div.2): dorijanlendvaj, SoulTch, pajenegod, AryaPawn, Rahul, mcdx9524, 300iq, Nemo, tfg
  • Phase 2 (Before we knew that old Div1D can be easily googled): Um_nik, Ari, benson1029, khulegu, Sad_reacts_only, TselmegKh
  • Phase 3 (Before few days to the round): mohammedehab2002, Kuroni, xuanquang1999, Maripium
• CF Admins: Thanks to MikeMirzayanov and his team for maintaining Codeforces and Polygon. I would like to say same sentence again as I said in my last round's announcement. Polygon is super great platform to prepare sports programming contest.

Followings are some fun things that I tried for this round:

• antontrygubO_o is the most intense coordinator I have ever met. He rejected lots of my problems. Some example of rejection comments are below:
  • This problem is too standard.
  • Don't ask people about theorem and formula.
  • This problem is appeared in recent ptz camp with higher constraints.
  • I don't like it.
  • Rock Scissor Paper makes statement messy, because some people don't know about it.
  • D2A should be easier than this one.
  • I've found generalized version of this problem in POI.
  • Isn't this obvious?
  • Your proof is wrong.
  • This problem is not very interesting.
  • This is too (censored).
• After lots of rejections, I tried my best to make problems to be interesting. I hope you like at least some of my problems.
• This round was originally supposed to be rated for Div.2 only. However, after we completed Phase 1 testing, we found that my round is too hard for Div.2, so we added more problems and made this round to be Div.1.
• In this round, statements will be even shorter than last contest.
• Even for some of problems which my coordinator approved, there were critical issues that made problems to be excluded. I will introduce some of my rejected problems which won't be used anymore in another post, after this contest ends.

I hope everyone can enjoy my third contest. Thanks in advance!

Hello, Codeforces!

I'm glad to invite you to my first round Codeforces Round #632 (Div. 2), which will take place on Apr/08/2020 17:35 (Moscow time).

"Thank you" time!

I'd like to thank:

• antontrygubO_o for coordination of the round.
• 300iq, nvmdava, aryanc403, antoshkin, lkosten, pavel-afonkin for testing and useful advices.
• MikeMirzayanov for great systems Codeforces and Polygon.
• CuriOusQuOkka for listening to my mumble while I came up with tasks.
• antontrygubO_o for coordination of the round (again).

You'll be given 6 problems and 2 hours to solve them. Point distribution will be announced as soon as possible.

Hope you will enjoy the round! Good luck and have fun!

P.S: YES, IT'S RATED.

UPD: Score distribution: 500 — 750 — 1250 — 1750 — 2000 — 2500.

UPD2: Congratulations to the winners!!

Div2:

• AnsuFati
• gmusya
• Alex_Wei
• sweetwrapper
• wjli

Wow, there is no unrated in div2 round!

All:

• jiangly
• MiFaFaOvO
• Roundgod
• summitwei
• tmwilliamlin168

UPD3: I will post solution in several hours.

UPD4: It was very long several hours, I'm very sorry for that :( Editorial

Hello, everyone! Codeforces Round #631 will be held at Apr/03/2020 17:35 (Moscow time).

The problems are almost from me(dreamoon_love_AA), except one problem of which the idea is from drazil and developed by me. Also we want to thank 300iq for helping me prepare the round, isaf27, tmt514, rowdark, yp155136, wangyenjen, n_dao107 and zj713300 for testing this round, and MikeMirzayanov for Codeforces and Polygon.

This is my third time organizing a problemset for a Codeforces round (my previous rounds: Codeforces Round #292, Codeforces Round #320).

Good luck and have fun!

UPD: Below is a message for you from MikeMirzayanov:

About two weeks ago, we completed the crowdfunding campaign dedicated to the 10th anniversary of Codeforces. Community help inspires and provides resources for the development and operation of the platform. Thanks! With this round, we want to say thank you to Denis aramis Shitov, for his significant contribution and support. It is valuable, important and very nice when people from the community lend a helping hand and congratulate. Thank you, Denis!

UPD2: Also thanks to Shik for testing the round!

UPD3: Score distribution:

• Div2: 500 1000 1500 1750 2500
• Div1: 500 750 1500 2000 2500

UPD4: link to tutorial

UPD5:

I won't say sorry that the pretests are not strong. Because I don't think the pretests must be strong in every contest.

But I still want to give congratulations to the winners:

div1:

1. Um_nik
2. tourist
3. Petr
4. ecnerwala
5. ffao

div2:

1. Z_m0mmy
2. hydd
3. fafafafafafa
4. timf1089
5. FrijolitoAzul

Among these winners, I want to especially congratulate Um_nik. I am quite excited when I see him solve all problems.

The contest is over; I hope you enjoyed it! The editorial is available here.

The 8th April Fools Day Contest will take place on Wednesday April 1st. This is a joke competition in which solving the problem is often easier than figuring out what the actual task is.

In this round you'll be given several weird problems and 2 hours to solve them. The contest will use ACM ICPC rules (no hacks, the standings are decided by the number of solved problems and penalty time earned on them), and it will be unrated. You can submit solutions in any language allowed by Codeforces, unless the problem says otherwise. To get an idea of what the contest will look like, you can check out the contests of the past years: 2012, 2013, 2014, 2016, 2017, 2018, 2019.

As usual, to enjoy competing in this round you'll need a sense of humor compatible with mine. Good luck, and have fun!

Hello Codeforces!

I am glad to invite you to my first official round Codeforces Round #630 (Div. 2), which will take place on Mar/31/2020 16:35 (Moscow time) (please note for the unusual starting time) and will be rated for all Division 2 participants.

You will be given 7 tasks and 150 minutes to solve them.

All tasks in this round were prepared by me. Hope that you will enjoy those tasks!

I would like to thank:

• pikmike for great coordination of this round, and the idea of solution of one task!

• Nanako, nezzar for useful discussion and testing this round!

• antontrygubO_o, McDic, vovuh, Flowerandyouth, socho, Oak_limy, Amori, Stresshoover, I1I1I11I1I1, defolaut, hx073269 and Pavlova for testing this round and invaluable suggestions!

• MikeMirzayanov for great systems Codeforces and Polygon!

To avoid queueforces, we will provide small amount but strong (hope so) pretests for first few tasks. Hope it works!

Score distribution will be announced later.

Good luck and have fun!

UPD1: Score distribution: 500-1000-1250-1250-1750-2250-3000

UPD2: Contest is over, and here is the editorial.

UPD3:

I am sorry that pretests were not as strong as I excepted.

Congratulations to the winners:

div1+div2:

1. vepifanov

2. xyz32768

3. PinkRabbit

4. 300iq

5. nuip

div 2:

1. xyz32768

2. sorry_to_tourist

3. camilla

4. jerome_wei

5. [user: _dawn]

people who were first to solve each task:

A: wangjunrui

B: MagentaCobra

C: okwedook

D: wangjunrui

E: GsjzTle

F: yooooooooo

G: GoGooLi

Lastly, thanks to Handsome2004 for the brilliant hack of E.

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Hello! Codeforces Round #629 (Div. 3) will start at Mar/26/2020 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.

Good luck!

</almost-copy-pasted-part>

Thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for help with testing the round!

UPD: Also thanks to Vitaliy kuviman Kudasov for testing the round!

UPD2: Editorial is published!

Hello Codeforces!

On Mar/23/2020 17:35 (Moscow time) Educational Codeforces Round 84 (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 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 7 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Ne0n25 Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all the participants!

Congratulations to the winners:

Congratulations to the best hackers:

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

UPD: Editorial is out

Hello, Codeforces.

I hope you wash your hands and feel great.

I added the support of 64-bit g++. If you are using Windows, you can easily install it via our minimalistic package manager PBOX running the command line pbox install msys2-mingw64-9.

Your solutions are compiled with the command line g++ -static -DONLINE_JUDGE -Wl,--stack=268435456 -O2 -std=c++17 program.cpp.

Now you can try to use int128 and other 64-bit specific features! In fact, I am slightly worried that the presence of such features may widen the gap between C ++ and other languages. Wait and see.

Currently, support for 64-bit C++ is experimental. For example, I would not be surprised if IO on it works slower in some cases (it is necessary to test!). I invite you to join the testing and experimentations. Share your impressions in the comments!