By KAN, 24 hours ago, translation, In English,

Hi all!

This weekend, at Sep/23/2018 16:05 (Moscow time) we will hold Codeforces Round 512. It is based on problems of Technocup 2019 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 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 Elimination Round authors are Ajosteen, BledDest and adedalic. Thanks to FCB1234 who authored the last problem for div. 1 round and arsijo for his help in coordination. This round would also be not possible without the help of our testers: winger, Um_nik, AlexFetisov, Denisson, thank you so much!

Have fun!

Div. 2 and the Elimination Round will feature 7 problems, preliminary costs are
250 — 500 — 750 — 1500 — 2000 — 2500 — 3000.

Div. 1 will feature 5 problems, preliminary costs are 500 — 1000 — 1500 — 2000 — 2500.

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By valkyrie, history, 6 days ago, In English,

Hello, Codeforces!

It's our pleasure to announce the the finals of the 11th Bubble Cup! Bubble Cup is a programming competition organized by Microsoft Development Center Serbia (MDCS). The contest will take place on Saturday, 22nd of September at 11:00 UTC+2 in Belgrade, and will last for 5 hours. Live results will be available on the official Bubble Cup website. Results will be frozen during the last hour of the competition. The winners will be announced at the closing ceremony.

The format of the competition is very similar to ACM-ICPC — teams consisting of up to three people are allowed, and they have one computer and five hours to solve problems without partial scoring. Ties are broken using the usual time penalty rules.

Just like in the previous years, there will be an online mirror of the finals here at Codeforces, starting on Saturday, 22nd of September at 12:35 UTC+2. Unlike in the previous years, the mirror will be on the same day as the onsite finals.

This year, the onsite competition is divided in two "divisions", called Premier League and Rising Stars. The two contests will have most of their problems in common, but the Rising Stars competition will feature some easier tasks targeted at high school contestants. We do not guarantee that every problems unique to Div2 is easier than every problem that is not.

Both of the contests will be mirrored here on Codeforces, with Premier League mapping to the Div1 contest and Rising Stars mapping to the Div2 contest. The mirror will use native Codeforces ACM-ICPC team contest rules.

Both contests will be unrated, due to the format and the length of the mirror being dissimilar to the standard Codeforces rated rounds. Note that this is a team contest, i.e. competing in teams up to three people is allowed. (Of course, you can also compete in a 1-person team.) There will be at least 9 problems in each division.

As of now, Codeforces does not support rating-based divisions in team contests, so we came with the following ad-hoc rule: teams with the maximum rated member having rating less than 1900 should enter the Div2 contest. Teams with the maximum rated member having rating at least 2100 should definitely enter the Div1 contest. The teams not covered by the previous two criteria are free to choose.

Here are the past Bubble Cup mirrors on Codeforces:

Bubble Cup 8 — Finals [Online Mirror]

Bubble Cup 9 — Finals [Online Mirror]

Bubble Cup X — Finals [Online Mirror]

The problems and their solutions were created by employees and interns of Microsoft: Milanin, ibra, balsa_knez, Kole, radras, fulu, pedja, niksmiljkovic, davidmilicevic97, FilipVesovic, yours truly, and many more. Most of the team works in MDCS.

We express gratitude to KAN and 300iq for round coordination, and MikeMirzayanov and the rest of the team for the great Codeforces and the wonderful Polygon platform. We thank testers DBradac and especially the extremely helpful knightL, for helping prevail various difficulties.

The full editorial, together with the statements and solutions of the tasks from the qualification rounds, will be available in the booklet section of the Bubble Cup website on Sunday. An editorial with short descriptions of solutions may appear on Codeforces before that.

Good luck to all participants!

EDIT: Congrats to everyone that competed! In total, there were over 800 teams that solved at least one problem.

The winners of Div1 are:

  1. Merkurev, I_love_Tanya_Romanova, Um_nik — a special congratulations for being the only team on the mirror to solve all problems, two of them in the last 5 minutes!

  2. LHiC — the best one-man team, with 9 problems solved

  3. Breakun, Hyunuk, ko_osaga — also solved 9 problems

The winning team of Div2 is:

  1. fengyecong, Als123, 200815147 — winning with three problems to spare!

This post will be updated again when the booklet is online, which should be before the end of the day in UTC+2. Also, onsite results won't be known until the awards ceremony in the evening.

Thanks all for participating!

EDIT 2: The editorial is up!

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By ditoly, history, 3 days ago, In English,

Hello everybody!

I'm glad to invite you to Codeforces Round #511 which will take place on Sep/21/2018 17:35 (Moscow time).

There will be 7 different problems in total, and 5 problems in each division. You will be given 2 hours to solve them.

The problems are prepared by me (ditoly), FallDream and ACMLCZH.

Thanks to 300iq who helps a lot in the round coordination, gritukan, V--o_o--V, demon1999, isaf27, cyand1317 for problem testing and MikeMirzayanov for the platform.

This is my first Codeforces round. Hope you can enjoy it. Good luck!

UPD: The scoring contribution:

Div.1 : 750 — 1000 — 1500 — 2000 — 2500

Div.2 : 500 — 1000 — 1750 — 2000 — 2500

UPD2: Congratulations to the winners!

Div. 1 :

  1. eds467

  2. scott_wu

  3. OhWeOnFire

  4. zemen

  5. ko_osaga

Div. 2 :

  1. Ranvan_Darkholme

  2. SqwrIwy

  3. wobeinimacao

  4. Egor_Gornak

  5. PrinzEugen

UPD3: The editorial is published. There are many things about problem-setting in it. Do not miss it.

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By huawei, 4 days ago, In English,

Dear Friends!

If you dream of realizing your ideas in new technologies and products used by a third part of the world's population — join Honorcup Marathon. It will be an unrated round for individual participation, as well as for teams of up to three people.

Take part in the round →

You will develop new method for determining blood pressure. The standard procedure for measuring blood pressure requires about a minute, during which the cuff compresses the artery in the hand. Since the procedure is relatively sophisticated, simpler methods of blood pressure estimation are potentially of great value. We suggest that you learn how to determine blood pressure based on the data from optical methods to determine changes in blood volume in the finger. Perhaps, your proposal will be implemented in one of Huawei products, and thereby help users reduce the risks of heart and vascular diseases!

At stake: high paid internships in Moscow, St. Petersburg or China (including transportation & accommodation expenses if needed). Also we have 9 smartphones for top 9 results:

  • 1-3 place: Huawei P20 Pro
  • 4-6 place: Huawei P20
  • 7-9 place: Honor 10

And, of course, TOP 30 participants will get T-shirts with Honorcup Marathon logo!

We accept solutions before 4th October, 19.59.59, Msc time. Winners will be awarded on 20th of October during the opening ceremony of 1/4 ICPC 2018 in Nagatino, Msk.

We will ask winners to provide the source code and description of the solution; the details can be discussed in a phone call. In case of reasonable doubt about the violation of the rules, we reserve the right to transfer the prize to the next participant. Thank you for understanding!

Don’t miss your chance!

Good luck to all!

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By PikMike, history, 4 days ago, translation, In English,

On Sep/20/2018 17:45 (Moscow time) Educational Codeforces Round 51 (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 Roman Ajosteen Glazov, Ivan BledDest Androsov and me.

Good luck to all participants!

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

Harbour.Space University is proud to announce new partnerships for this year’s Hello Barcelona Programming Bootcamp — VTB and Indeed Tokyo, with the addition of team sponsors Phaze Ventures and Spark Labs.

VTB, the largest international bank based in Eastern Europe, continues to be an official partner of our Hello Programming Bootcamp series, adding further quality to the 3rd edition of the Hello Barcelona Programming Bootcamp by bringing their own participants, as well as by supporting top teams from around the world.

Indeed Tokyo is Japan’s branch of the #1 employment website in the world, giving job seekers free access to millions of jobs from thousands of company websites and job boards. As they sponsor for the second year in a row, Indeed continues to offer the best job opportunities to the boot camp participants as they gather in Barcelona from September 26 to October 4, 2018.

UPD: There was a bug in testset and validator for problem F, we are currently fixing the issue. The statement included the correct resrictions. We will rejudge all the solutions as soon as possible. The round can become unrated, we are discussing this at the moment.

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 kmjp 6 210
2 MrDindows 6 223
3 elykuil 6 242
4 Nisiyama_Suzune 6 274
5 Fekete 6 274

Congratulations to the best hackers:

Rank Competitor Hack Count
1 halyavin 299:-14
2 Laggy 100:-10
3 greencis 29:-2
4 Volkov_Ivan 19
5 dorijanlendvaj 13
694 successful hacks and 497 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A traxexeuler 0:03
B answhldkd 0:02
C ainta 0:06
D greencis 0:07
E tfg 0:38
F baggins 0:26
G yasugongshang 0:56

UPD2: We investigated the issue to get the following results. 10 people were noticeably affected (that took them more than 3 minutes of the working time). Round will surely be rated for other participants. As for the affected participants, we will look into the rating changes and revert them in case they are negative (set the participant into the unofficial participation mode).

UPD3: Editorial is out

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By Vovuh, 7 days ago, translation, In English,

Hello, Codeforces!

Codeforces Round #510 (Div. 2) will start at Sep/17/2018 11:05 (Moscow time). The round will be rated for Div. 2 contestants (participants with the rating below 2100). Div. 1 participants can take a part out of competition as usual.

The round will be rated for the Div. 2 participants (for everybody with rating less than 2100). The statements will be available in Russian and English languages.

This round is held on the tasks of the school stage All-Russian Olympiad of Informatics 2018/2019 year in city Saratov. The problems were prepared by PikMike, fcspartakm, Ne0n25, BledDest, Ajosteen and Vovuh. Great thanks to our coordinator _kun_ for the help with the round preparation! I also would like to thank our testers DavidDenisov, PrianishnikovaRina, Decibit and Vshining.

You will be given six problems and two hours to solve them. Scoring system will be announced traditionally closer to round start. :)

UPD: The scoring distribution is 500-1000-1500-2000-2250-2750.

UPD2: Editorial

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By Ajosteen, 10 days ago, translation, In English,

Hello, community!

Codeforces Round #509 will be held on Sep/16/2018 13:35 (Moscow time). The round will be rated for Div. 2 contestants. There will be 6 problems for 2 hours. Please, notice that the start time is unusual.

The round will be rated for the div. 2 participants. The statements will be available in Russian and English languages.

The round will start 2 hours after the start of the Qualification Stage, so they will finish around same time. That's why we ask the participants of the Quals to stay silent and don't share the statements of the contest with anyone. Unfortunately, we cannot add all the problems from Quals to the round, it will contain only six problems.

The problems for the official contest were prepared by the guys from the jury in the person of Alex fcspartakm Frolov, Adilbek adedalic Dalabaev, Ivan BledDest Androsov and me.

We also would like to express our gratitude to Anton arsijo Tsypko for coordination of the round and Mike MikeMirzayanov Mirzayanov for the permission to make a mirror and Codeforces and Polygon platforms. Also big thanks to the testers: IlyaLos, Perforator, kuviman, HolkinPV, zubec, StasyaCat, Karasick for testing.

As usual, the scoring distribution will be announced just before the round.

Good luck!

UPD: Scoring Distribution: 500-1000-1500-2000-2500-3000

UPD2: Editorial

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By Radewoosh, history, 2 weeks ago, In English,

Hello, codeforces!

Because after Round #507 sad men in suits visited me in my flat, this time I won't write about any task from the future. Instead, this blog will be about my own trick. I said "my own," but probably some of you have already heard about it or even figured it out, but I've developed it by myself, so I consider it as my own.

In particular, it's GEOMETRY TIME!!!. But please, don't escape already. I also don't like this topic so much, that's why I really like this trick. Let me tell you a story from one onsite Polish contest, which took place a few months ago. I was thinking about one of the problems, and I've figured out that I had to do some binary-search (on doubles) and then check if a set of half-planes has a non-empty intersection. The answer would tell me in which direction should I turn in the binary search.

Firstly, I grabbed my head, because I've never written an intersection of half-planes. I had my acm library with Errichto's codes inside, but my knowledge in usage of his part was limited to copy-pasting FFT and Rho-Pollard. Not only I, but also Swistakk figured out the thing about binary search and was trying to intersect half-planes normally, but he failed (we still aren't sure why, probably because of precision issues). Then, I reminded myself a task from eliminations to BubbleCup 2017 (you can find it here), which I solved with the mentioned trick.

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