By Errichto, 5 hours ago, ,

Hi.

On Wednesday at 9:05 CET / 8:05 UCT you can participate in the GYM version of the finals of 2017-2018 Russian Olympiad in Informatics (ROI), Day 1. And on Thursday there will be day 2, same time.

5 hours, 4 problems, IOI-style scoring with subtasks. Statements will be available in three languages: English, Russian, Polish.

We wanted to use those problems in a camp in Warsaw so we had to import the problems to some system anyway. Then why not Polygon+Codeforces and thus allowing everybody to participate? Huge thanks to MikeMirzayanov for helping me with using GYM.

I will post a very short editorial in English here, after the contest.

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By MikeMirzayanov, 2 days ago, translation, ,

Hi Codeforces!

Here are some recent improvements here and in Polygon.

### Weak and Leaked Passwords

We often hear about password leaks from various services. Considering that having common passwords is a common (but insecure) practice, we've improved Codeforces and Polygon to identify weak or leaked passwords. If on the top of the website you see a message that your password is not secure, then just change it immediately.

### Type of the round when creating a contest proposal

This item improves our work with the writers. When creating a contest proposal, please indicate the type of a round. Leave the field empty only if you don't know the type of the round (it is strange).

### Calendar

We've fixed errors when synchronizing official Codeforces rounds with the calendar. Now everything should be correct.

### I trust this user

Currently, Codeforces provides a mature infrastructure for organizing contests, olympiads and trainings. With the help of domain groups and mashups, competitions of various levels were hosted on Codeforces. The organizers are sometimes not regular users of Codeforces rounds and do not have rights to some of the actions. Now, any red user can confirm his trust in another account, and he will get the right to: write comments/posts, create private groups, create mashups. I hope this will save me from a certain routine of processing such requests.

### Confirmation via email when entering Polygon

When you sign in Polygon, your IP-address and browser will be verified. If you didn't use them in the recent past, then you may be asked to sign in with a confirmation email. In this case, just follow the secret link that comes to your email.

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By PikMike, history, 5 days ago, translation, ,

Hello Codeforces!

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 participants!

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

Hello Codeforces!

We want to remind you about the two fully funded scholarships we currently have available:

Master’s in Data Science Scholarship & Master’s in Robotics Scholarship

Both scholarship opportunities include: - Full coverage of the Programme’s tuition fee (€23,000 value) - 3 hours of study a day at Harbour.Space University - 4 hours of internship a day with one of our industrial partners - €12,000 euros a year (living allowance)

If you’re interested in applying for the Robotics Scholarship, apply here.

If you want to apply for the Data Science Scholarship, fill out the form below and we will contact you about the next steps.

GO TO FORM

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 QDEZ604 7 250
2 dotorya 7 254
3 300iq 7 586
4 dreamoon_love_AA 6 165
5 Hazyknight 6 169

Congratulations to the best hackers:

Rank Competitor Hack Count
1 Haunted_Cpp 8
2 7qk 4
3 Jobaidul 3
4 Abu_Musa_99 3
5 aihay 2
37 successful hacks and 149 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A Sonechko 0:01
B usertab34 0:04
C KhaleD_ 0:04
D edisonhello 0:02
E Roundgod 0:23
F QDEZ604 0:38
G 300iq 0:44

UPD: Editorial is out

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By Jeel_Vaishnav, history, 5 days ago, ,

Hi everyone!

I would like to invite you to my second Codeforces round, which I have created with my friends Ashishgup and Vivek1998299.

With that said, I bring to your attention our new Codeforces Round #548 (Div. 2) that will take place on Mar/21/2019 18:35 (Moscow time). If your rating is less than 2100, this round will be rated for you; otherwise, you can participate out of competition.

I would like to thank Ashishgup and Vivek1998299 for their help with preparing problems, V--gLaSsH0ldEr593--V, mohammedehab2002 and Um_nik for testing the problems and _kun_ for coordinating our round. I would also like to thank MikeMirzayanov for the awesome Codeforces and Polygon platforms.

You will be given 6 problems and 2 hours to solve them. Scoring distribution will be announced later.

Good luck! :D

UPD1: Shortly after the contest, we'll be on the community Discord server to discuss the tasks.

UPD2: Score distribution is — 500-1000-1750-2250-2500-3000

UPD3: Editorial

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By MikeMirzayanov, 9 days ago, translation, ,

Hello, Codeforces!

I am pleased to invite you to Codeforces Round #547 (Div. 3), which will start on Mar/19/2019 17:35 (Moscow time). Everyone whose current rating is strictly less than 1600 is invited to participate officially. All others can take part out of the competition.

It so happened that the schedule of this month is not replete with rounds (coordinators, we hope for you!). Therefore I decided to partially correct the situation. All the problems of this round were invented and prepared by me on the last day of Hello Muscat Programming Bootcamp 2019 and on flights from Muscat to St. Petersburg. I even specially noted the time for preparation: for the current moment (the problems are ready for testing) I spent about 6 hours on their preparation, including inventing some of the problems. I really like working on problems, this is something at the intersection of creativity and programming. I really hope you enjoy the result of my work.

I am in Oman while writing the problems for the round.

The round will be hosted by rules of educational rounds (extended 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 6-8 problems for 2 hours to solve them.

Note that the penalty for incorrect submissions in this round 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.

I hope a little later a list of thanks to testers will appear instead of this paragraph. So far I only plan to give the round to testing. Many thanks to the testers ivan100sic, KrK, Benq, I_love_Tanya_Romanova, nhho! UPD: And extra thanks to more testers Pavs, PikMike, Narts, anon20016, Stresshoover, Ivan19981305.

Good luck on the round
MikeMirzayanov

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By MikeMirzayanov, 13 days ago, translation, ,

Hello!

We supported the rendering of LaTeX-formulas with MathJax in new posts and comments. Now the formulas will be as beautiful as in problem statements. Drawback: they are displayed not immediately, but redrawn after the page is displayed. Old posts and comments are displayed in the old way (already a lot of old content, backward compatibility is very important). Note that if you edit old post, it will still be displayed in the old style.

Here are some example: $1 \le n \le 10^{12}$,  $c = \sqrt{a^2+b^2}$,  $i\hbar\frac{\partial}{\partial t}\left|\Psi(t)\right>=H\left|\Psi(t)\right>$.

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By DmitryGrigorev, history, 2 weeks ago, translation, ,

Hi, Codeforces!

I`m glad to invite everybody to the #546 Codeforces round, which will be held on Monday, March 11, 2019 at 19:35. The round will be rated for all participants from the second division (with rating below than 2100). As usually, we will be glad to see participants from the first division out of competition!

Problems for the round have been proposed by Fedor osaaateiasavtnl. Ushakov, Stepan IbragiMMamilov Stepkin, Alexey usertab34 Roze, Denis Denisson Shpakovskij and Alexander Ralsei Gladkov.

The round have been prepared by us, Dmitry DmitryGrigorev Grigoryev, Fedor osaaateiasavtnl. Ushakov, Semyon cookiedoth Savkin and Dmitry TheWayISteppedOutTheCar Piskalov.

We'd like to give thanks to Ildar 300iq Gainullin for excellent coordination of the round, Grigoriy V--gLaSsH0ldEr593--V Reznikov, Alexey Aleks5d Upirvitsky and Mohammed mohammedehab2002 Ehab for testing and to Mike MikeMirzayanov Mirzayanov as well for his unbelievable Codeforces and Polygon platforms.

You will receive 5 problems and 2 hours for solving it. During the round you will be helping for an extraordinary girl Nastya, who is studying in an usual school in Byteland.

Score distribution will be announced, traditionally, closer to the start of the contest.

UPD Score distribution is standart — 500-1000-1500-2000-2500

We're looking forward your participation.

UPD2 Thank you for your participation in the contest!

List of the winners of the contest:

Div.2

Div.1 + Div.2

My frank congratulations for all the winners!

The editorial will be posted very soon. We apologize for delay.

UPD3

The editorial

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By _kun_, 3 weeks ago, translation, ,

Hello!

Right now happens the first tour of the Open Olympiad in Informatics, and tomorrow will be the second one. This contest is prepared by Moscow Olympiad Scientific Committee that you may know by Moscow Team Olympiad, Moscow Olympiad for Young Students and Metropolises Olympiad (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541)

Open Olympiad consists of the most interesting and hard problems that are proposed my a wide community of authors, so we decided to conduct a Codeforces regular round based on it, which will happen Mar/08/2019 12:05 (Moscow time) and will be based on both days of the Olympiad. Each division will have 6 problems and 2:30 hours to solve them.

We kindly ask all the community members that are going to participate in the competition to show sportsmanship by not trying to cheat in any manner, in particular, by trying to figure out problem statements from the onsite participants. If you end up knowing some of the problems of Moscow Open Olympiad (by participating in it, from some of the onsite contestants or in any other way), please do not participate in the round. We also ask onsite contestants to not discuss problems in public. Failure to comply with any of the rules above may result in a disqualification.

Problems of this competition were prepared by V--gLaSsH0ldEr593--V, isaf27, Flyrise, _kun_, GlebsHP, ch_egor, Zlobober, qoo2p5, grphil, achulkov2, Schemtschik, akvasha, mingaleg, V--o_o--V, wrg0ababd, guided by ch_egor, _kun_, GlebsHP, Zlobober and Helen Andreeva.

Problems for second division were prepared by KAN and MikeMirzayanov, to who we also want to say thanks for the Codeforces and Polygon systems.

Good luck everybody!

UPD: Congratulations to the winners!

Div.1

Div.2

The editorial will appear soon

UPD: The editorial

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By Vovuh, history, 3 weeks ago, ,

<copy-pasted-part>

Hello! Codeforces Round #544 (Div. 3) will start at Mar/07/2019 18:05 (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. 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.

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 Mikhail PikMike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round.

Good luck!

I also would like to say that participants who will submit wrong solutions on purpose and hack them afterwards (example) will not be shown in the hacking leaders table.

</copy-pasted-part>

UPD0: I also would like to thank Stresshoover, dreamoon_love_AA, Nebuchadnezzar and nhho for help in testing the round!

UPD1: Editorial is published!

UPD2:

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 MoNsTeR_CuBe 7 340
2 try_agian 7 370
3 HurmousDay 7 396
4 AyaOtonashi 7 404
5 N_o_o_B 7 437

Congratulations to the best hackers:

Rank Competitor Hack Count
1 greencis 72:-31
2 jhonber 30:-1
3 Milkdrop 22:-15
4 awasd 16:-3
5 MarcosK 12:-5
269 successful hacks and 316 unsuccessful hacks were made in total!

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

Problem Competitor Penalty
A friendly_potato 0:02
B OFAKMKOFZ 0:04
C MbahFaishol1937 0:03
D AyaOtonashi 0:08
E nvwa 0:22
F1 elevendigit 0:15
F2 XXMihaiXX969 0:21