Hello, Codeforces!

I and cannor147, as students of ITMO University, joined the Codeforces team in June. From June to October, we mainly dealt with the development of the Polygon platform. In this post, we would like to present to you a list of what we have done during this time. This list does not include minor bug fixes or any improvements that are invisible to users.

PIN codes for problems and contests

Sometimes very important contests and problems are being developed in Polygon. In such cases, a leader of the jury may be worried about data leaking. For example, it can be so because of the weak password of another member of the jury. PIN code is an additional factor of confirmation the access for the problem or contest and it can be set up only by the owner. It is assumed that the PIN code will be sent in another secure way.

There is a link Create Pin for the owners in the contest interface:

If a contest or a problem has the PIN code, you need to type it before continuing.

You can manage the PIN code of the problem in the tab Manage Access in the problem interface. The owner can create the PIN code or copy the PIN code from a contest that contains the problem.

If you use Polygon API, there is a way to send requests for working with problems or contests, that have the PIN code. You have to provide a new additional parameter “pin” in your requests.

Groups of contests

Polygon grows up and the number of contests in Polygon grows up too. Sometimes you want to group some contests. For example, it seems convenient to group contests from the same programming workshop. Now in Polygon you can group some contests for faster management of the access rights for them.

I'm sadly announcing that a2oj.com (A2 Online Judge) will be retiring by end of 2019, I'll shut it down at midnight on New Year's Eve. It was something I took care of for about 10 years.

I'm really sorry, but I prefer not to explain my reasons, so please don't ask me why I'm doing this, it was hard enough for me to make this decision, and also please don't try to convince me to change my mind.

I'd like to say thank you to everyone who used it, and please accept my sincere apologies for shutting it down.

If you have something good to say about A2OJ (how you used it or how it helped you in any way), I'd love to read that, please send it to the following email (or in a comment here): bye@a2oj.com

Also please feel free to take a copy of any data you can access, and if you need some data in a specific format, please send your request to the following email: bye@a2oj.com (if the data isn't public, make sure to send from your registered and verified email which can access this data). I'll do my best to fulfill all requests.

Please only use the above email, because soon I'll be deactivating my personal Facebook account again, I'll also deactivate A2 Online Judge.

Edit 1: I'll keep a static version of all Ladders & Categories.

Edit 2: Here's how I generated the ladders, in case if anyone wants to implement it: https://codeforces.com/blog/entry/47442

Hi guys!

Glad to invite you to Codeforces Round #599 to be held this Nov/06/2019 18:05 (Moscow time)!

My name is Evgeny Vihrov, this is already my 6th Codeforces contest as an author. To introduce myself, I have participated twice in the ACM ICPC Finals (2012, 2014) and currently I am co-coaching teams for the ICPC at the University of Latvia. This is my first solo round, and it took 3.5 years to make! (the last one was #347 with Alex_2oo8).

In this contest you will have to help Ujan deal with his renovation issues. Hopefully, everyone will find a problem matching their taste!

Huge thanks to arsijo for coordinating the preparation of the contest and for the patience with the frequent delays. :) Thanks to Xellos, Origenes, KAN and opukittpceno_hhr for generously testing the round. And as always, thanks to MikeMirzayanov for the panem et circenses Codeforces and Polygon systems!

Wish you an exciting round!

UPD1: McDic is joining as a coauthor of the contest (reasons to be revealed later)!

UPD2: Scoring:

Div. 1: 500-1000-1500-2000-2500

Div. 2: 500-500-750-1500-2000-2500

UPD3: Thanks for participating! Congratulations to the winners!!!

Div. 1:

1. Benq
2. wxhtxdy
3. ecnerwala
4. AndreySergunin
5. oxytocyna

Div. 2:

1. hakobdilif
2. is1813r
3. Fype
4. pizzadelivery
5. tdas

UPD4: The editorial will be available tomorrow, sorry for the delay. :((

UPD5: The reason behind McDic entering as a coauthor is that one problem was exactly identical to some problem from some Codeforces round. We found out about it only at the last day before the contest, and McDic generously allowed to use his problem.

UPD6: Editorial is posted.

The MEX Foundation Contest #1 (supported by AIM Tech) that was held in the 37th Petrozavodsk Programming Camp now available in the Gym.

The authors of the contest are UnstoppableSolveMachine, cookiedoth, egor.lifar. The problems are of a good quality, a number of participants can approve it.

Special thanks to gritukan for useful advices, LHiC for testing the contest, V--gLaSsH0ldEr593--V for inspiration and AIM Tech Members for the problem review.

UPD: The editorial is published!

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Hello! Codeforces Round #598 (Div. 3) will start at Nov/04/2019 16:15 (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!

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.

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Good day, Codeforces! Or in my language, magandang araw, Codeforces!

Codeforces Round #597 (Div. 2) will be held on Nov/01/2019 17:35 (Moscow time). Is it rated? Yes, but only for participants below 2100 rating.

Of course, this round is not made by me alone. So, I would like to thank the following people for their help in making this round possible:

• coordinator PikMike, for coordinating my round even when he was very busy;
• testers antontrygubO_o, McDic, 300iq, adedalic, isaf27, farmersrice, NeverBeNutella, Vovuh, CaseRuten,Stresshoover, ZeroAmbition, Pavlova, defolaut, and Arpa, for testing problems and giving very valuable feedback;
• and of course, MikeMirzayanov and Codeforces staff, for providing us with the amazing Codeforces and Polygon platforms!

There will be 6 problems, and you will be given 2 hours to solve them.

The scoring distribution is as follows: 750-750-1250-1750-2250-2500.

I hope you enjoy the round!

Update: editorial is out now

Hello, Codeforces!

The China Collegiate Programming Contest (CCPC) is a competitive programming contest series for college students in China, organized by the CCPC Committee, which consists of coaches of the competitive programming teams of Chinese universities. It started in 2015, and this year is the 5th edition of CCPC. There are 4 onsite CCPC contests this year, including three regional contests in Qinhuangdao, Harbin and Xiamen, as well as the CCPC Final in Beijing. Many Chinese universities use CCPC as an opportunity to practice before the ICPC regionals.

The 2019 CCPC Harbin Site has recently ended on October 13 in Northeast Forestry University. A total of 272 teams, most of whom were selected from the preliminary online contest, took part in the official onsite contest in Harbin. The problems for this contest were mostly prepared by retired ICPC participants of Zhejiang University, and the head judge was me.

We are glad to invite you to participate in its online mirror: The 2019 China Collegiate Programming Contest Harbin Site in Codeforces::Gym! Please note that the mirror contest will start at Saturday, November 2, 2019, 18:00 (UTC+8). Click on the link to see when it starts in your timezone. We will be able to answer your questions during the mirror contest. The ghosts of the onsite participants are available, so you may take advantage of it.

This contest uses ACM-ICPC rules and of course, it is unrated. Team participation is recommended, but it is also possible to participate individually. As usual for Gym contests, you may register for this contest 6 hours before it starts, and you will be able to virtually participate and upsolve the problems after it ends.

My thanks go to:

• Volunteers and staff from Northeast Forestry University for holding a very successful onsite contest.

• Problem authors: lsmll, quailty, Claris, jiangshibiao, shb123 and Reku.

• Testers: izban, 300iq, and many members of the competitive programming team of Zhejiang University, some of them are: Todobe, wxx_louisa, zx2017, SoSad, zhangqingqi and lyk248289469.

• MikeMirzayanov for the powerful Polygon and Codeforces system.

• The CCPC Committee and the sponsors of the onsite contest.

We kindly ask everyone who has already know the problems not to participate or discuss them before the mirror contest has ended. Hope you enjoy the problems!

UPD: Contest has ended, thanks everyone for your participation. Here is the link to the official editorial, unfortunately it is in Chinese. But feel free to ask in the comments if you have any questions about the problems.

Hello!

ICPC Southern and Volga Russian Regional Contest (Northern Eurasia) 2019 has ended on October 15. There were 76 teams onsite in Saratov, most of them were invited because of their result on the qualification stage.

On Oct/27/2019 12:35 (Moscow time) will start online-mirror 2019-2020 ICPC, NERC, Southern and Volga Russian Regional Contest (Online Mirror, ICPC Rules, Teams Preferred).

In this contest I play a role of Cheif Judge and the jury teams consists of ex-participants of ICPC from Saratov and jury members from other cities. Many thanks to all of them! I hope you will like the problems!

I invite ICPC teams and individual participants of Codeforces competitions to take part! Sure, the contest will be unrated.

— MikeMirzayanov