By Hasan0540, 2 weeks ago, ,

Hello everyone!

I would like to invite you to participate in Codeforces Round #480 (Div. 2), it will take place tomorrow, May/08/2018 18:05 (Moscow time).

The round consists of 6 problems and you will have two hours to solve them.

The problems were prepared by me with great help from linkinu and 1am. I would like to thank KAN for his great efforts in reviewing the problems and for his suggestions, it is really amazing to see the work done behind every round. Also thanks to Tommyr7, Livace and mike_live for testing the problems, and to arsor for translating the statements into Russian.

This is my first round on Codeforces, I hope that you will find some interesting problems for you.

Note that the round is rated for everyone with rating below 2100.

Good luck and have fun!

UPD: Congratulations to the winners:

Div. 2:

Div. 1+2:

UPD1: Editorial

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By Vovuh, 2 weeks ago, ,

Hello!

Codeforces Round #479 (Div. 3) will start on May 6 (Sunday) at 14:05 (UTC). It will be the first Div.3 round in the history of Codeforces. You will be offered 6 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. Probably, participants from the first division will not be at all interested by this problems. And for 1600-1899 the problems will be too easy. 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.

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 Ne0n25 for testing the round.

UPD: Thanks a lot to testers dreamoon, eddy1021, step_by_step and egor.lifar who agreed to test the problems and found the mistakes. Now we are ready to start the round!

I hope that you will like the problems. If suddenly something does poorly with difficulties of the problems, then we will adjust the difficulties in the next Div. 3 rounds.

Briefly about myself. My name is Vladimir Petrov, I am studying at the 3rd year at Saratov State University and from the high-school I am studying at SSU Olympiad Training Center. In ICPC I participate in the team "Saratov SU Daegons" with PikMike and Ne0n25. I like reading and watching science fiction. I’ve read "Song of Ice and Fire" 3 times and wait for publication of 2 more volumes.

Good luck!

UPD2: Editorial

UPD3:

Congratulations to the winners (official results):

Rank Competitor Problems Solved Penalty
1 cMartynas 6 69
2 nimphy 6 117
3 iman12 6 124
4 mandinga 6 128
5 raffica 6 144

Congratulations to the best hackers:

Rank Competitor Hack Count
1 greencis 36:-8
2 Tlalafuda__Tlalafu 10:-1
3 STommydx 9:-1
4 dalex 8:-7
5 dreamoon 4:-3
6 shnk 2

97 successful hacks and 297 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A kuzmoid 0:01
B c650Alpha 0:04
C Milhous 0:08
D Milhous 0:11
E s0mth1ng 0:09
F DoveDragon 0:14

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By vlecomte, history, 2 weeks ago, ,

Hi Codeforces,

As I mentioned before, as part of my Master's thesis, besides my book I am organizing a contest with exclusively geometry problems to showcase some types of problems or techniques that I think could be cool to see in the future in ICPC and other contests.

It will take place this Sunday 08:00 UTC in the Gym (the link will be http://codeforces.com/gym/101793, registration should open 6h before and remain open during the contest). There will be 4 problems to solve in 3 hours.

The problem should be particularly relevant for students participating to the ICPC. But the problems will be very hard, so I think they can be interesting to everyone with a sufficient level in geometry.

The problems will be roughly sorted by estimated difficulty, but please read all the problems, as you might find that you feel more interested by one of the "harder" problems. The statements will be given all together in a PDF attachment. The samples will be in the PDF as well as on the problem pages.

Since it's my first time organizing a whole contest by myself, I hope everything will go smoothly. I would like to thank yunoac for the precious feedback on the tasks (and of course his amazing support during my whole thesis), Nicolas16 for beta-testing the problems in a tight schedule, and of course MikeMirzayanov for the great Codeforces and Polygon platforms.

I hope many of you will participate to the contest and enjoy the problems. See you for the editorial!

PS: You might want to revise your 3D geometry. ;)

UPD: The length is confirmed to be 3 hours. The contest will be held under ICPC rules. You can participate either individually or in a team.

UPD2:

Congratulations to the winners:

who also happen to be the only participants to solve at least one problem.

Thanks to everyone for participating, the editorial is coming in a moment!

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By MikeMirzayanov, 3 weeks ago, translation, ,

Hello, Codeforces!

It's time for news. I hope you will enjoy!

• We reduce the rating bound for the orange color. Thus, now the orange rating (and the Master title) will start from 2100 rating units.

• The lower bound of the rating for legendary grandmasters is increased to 3000 rating units. Thus, right now in the community, 14 participants meet this requirement. Real legends!

• For rounds like "Div. 2 Only" the upper bound of the rating for official participation is increased. Now everyone whose rating is less than 2100 (i.e., before masters) will be able to register for such rounds to participate officially, their rating will be updated based on the results of the round. We do not plan to increase the complexity of Div. 2 rounds. Practice shows that the problems of such rounds are interesting and useful for participants "below the orange".

• For parallel Div. 1 and Div. 2 rounds we don’t change the rating bound between divisions. So Div. 1 edition of the round continue to include participants with the rating from 1900 and above.

• As an experiment, we plan to host rounds of simplified complexity (Div. 3). In such rounds, the official results will include participants with ratings less than 1600. We plan to include in these rounds simple training problems that will help beginner participants to gain skills and to get new knowledge in a real contest. Since even in the Div. 2 rounds regularly some Div. 1 users register new account and take high place, we also expect such unsportsmanlike behavior in the Div. 3 rounds. We will exclude from the official standings of Div. 3 rounds and put in a separate rooms all those who can’t be reliably called to be a real participant. Accounts that materially participated in less than 2 rating rounds (materially means solved at least one problem there) before the start of the Div. 3 rounds, and those who have ever gained 1900 or more rating units will not get into the official standings and will be assigned to separate rooms. However, this does not mean that there is no rating recalculation for them. Thus, the rating will be updated for all users whose rating is strictly less than 1600 at the time of the start of a round. Perhaps we will experiment with the definition of who should be considered a reliable Div. 3 participant. And thanks to VLamarca for the post about idea of Div.3 rounds!

Updating the boundaries of ratings and changing colors is not an instantaneous process. For this reason, the website may still have outdated information for some time. We are working to apply the announced changes during the day.

I hope you enjoy this news.
MikeMirzayanov

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By Rollo, 3 weeks ago, ,

Hello codeforces!

I'm glad to announce that codeforces round #478 for the second division will take place on Tuesday, May 1st 17:05 MSK. First division participants can also take part out of competition.

Great thanks to Nikolay Kalinin (KAN) and Fudail Hasan (fudail225) for helping me prepare the contest, to Mike Mirzayanov (MikeMirzayanov) for the great Codeforces and Polygon platform, Many thanks for Amr Mahmoud (AmrMahmoud ) Tameem Zabalawi (timo14z), AmirReza PoorAkhavan (Arpa), Alexey Ilyukhov (Livace), Hag Ahmad (Reckt), Nikita Bosov (neckbosov) and Andrew Rayskiy (GreenGrape) for testing the round.

You will be given five problems and two hours to solve them. The scoring distribution will be published soon. Good luck everyone!

I hope you'll enjoy my round. I wish everyone good luck and high rating!

UPD1: problem scores: 500 — 1000 — 1500 — 2000 — 2500

UPD2:

Congratulations to the winners

1- kmjp

3- Llamap.

4- E869120

Div.2 winners:

1- Llamap.

UPD3 : Tutorial is out!.

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By Vovuh, history, 3 weeks ago, translation, ,

Hello Codeforces!

On April 30, 17:35 MSK Educational Codeforces Round 43 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 Div. 2. It 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, Roman Ajosteen Glazov, Adilbek adedalic Dalabaev and me.

We'd like to thank Ivan BledDest Androsov and Maksim Ne0n25 Mescheryakov for the help in preparing the round.

Good luck to all participants!

UPD: The round will contain 6 problems instead of 7.

UPD2: Editorial

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 dotorya 6 150
2 I_love_Tanya_Romanova 6 276
3 uwi 6 324
4 nuip 6 327
5 dreamoon 6 328

Congratulations to the best hackers:

Rank Competitor Hack Count
1 hryniuk 66:-4
2 Aemon 65:-13
3 saw.ai 56:-2
4 uwi 57:-12
5 im0qianqian 40:-1

777 successful hacks and 656 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A 300iq 0:00
B I_love_Tanya_Romanova 0:05
D dotorya 0:26
E djq_cpp 0:21

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By KAN, 3 weeks ago, translation, ,

Hi everyone!

Tomorrow, on the April 29, 2018, at 13:05 UTC we are holding the third round of VK Cup 2018 championship. This is the final online round, the next round is the final round in which top 20 teams from this round advance.

At the same time with the official round, we are holding parallel rounds for both divisions. Join them and see if you can beat top Russian-speaking teams! Top50 in the "Div1 Edition" contest will get t-shirts.

All rounds are rated, their duration is 2.5 hours.

The authors of the problems are Zlobober, Endagorion and me. Thanks qwerty787788 and gritukan for their great help in round preparation!

Good luck!

Congratulations to winners!

1. V--o_o--V, LHiC — solved all problems, two problems ahead the runner-up!
2. senek_k, demon1999
3. sinesight, SpyCheese
4. Melnik, hloya_ygrt
5. egor_bb, Nikitosh

Mirror for the first division:

Mirror for the second division:

The editorial is here, thanks all for participation!

Announcement of VK Cup 2018 - Round 3

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By MikeMirzayanov, 4 weeks ago, translation, ,

Hello!

This blog post is about the end of the crowdfunding campaign dedicated to the 8th anniversary of Codeforces. Everything worked out. Hooray!

For us, it is very important to support not only in terms of the collected budget, but as a powerful indicator that Codeforces is important to you. It was very pleasant to read words of gratitude and congratulations. Thank you!

We received more than 1000 donations from community members from around the world. For 45 days we've collected more than $60000 dollars. The collected funds will allow us to continue to move forward, to please you with new contests and improvements of the system. I am happy to report that starting in May 2018, we will be able to slightly increase rewards for problem writers. Round type USD Rubles Div 1 + Div 2$250+*$150=$400 26000 rub
Div 2 $125+*$75=\$200 13000 rub

We tie the money paid in rubles to the Central Bank of Russia exchange rate, rounded to the closest sum in rubles divisible by 5 (according to the rules of mathematical rounding). The table shows the values that were up-to-date when this post was published. An asterisk marks the bonus that is given if the round is prepared in time and without major issues in problems.

In addition, the collected funds will help to increase a reward of the problem coordinators KAN and [user:gritikan]! Guys, you're doing a very important job, thank you for that!

Improvement of Codeforces hardware has already been launched, which will help improve the stability of the system and keep up with the growth of the audience.

To all those of you who are expecting a gift from us (certificate, T-shirt, hoodie), I remind that it is necessary to fill in or update the information in the profile about the delivery address. Please do not delay this!

Thank you again for your support!

MikeMirzayanov