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

Topcoder SRM 740 is scheduled to start at 12:00 UTC -4, Oct 20, 2018. You will be able to register for the SRM in the Arena or Applet 4 hours prior to the start of the match. Registration closes 5 minutes before the match begins, so make sure that you are all ready to go.

Editorials: https://www.topcoder.com/blog/single-round-match-740-editorials/

T-shirts: T-shirts will be awarded to the following members*:

  • Top 4 and 2 Random participants having scores > 0 in Division I

  • Top 4 and 2 Random participants having scores > 0 in Division II

*Only those members who registered on Topcoder on or before 09:00 UTC -4 October 18, 2018 are eligible for winning T-shirts.

Featured Problem Writer: misofmisof

Interested in writing problems for Topcoder Matches? Learn more and submit your ideas here.

TCO19 Points Leaderboard: https://tco19.topcoder.com/home/algorithm/algorithm-leaderboard

Topcoder Java Applet: https://drive.google.com/file/d/1gVJZxhWYMuUNx3PfSSTkkk-b9AeJkL4j/view

Hope to see most of you competing! All the best!

Next SRM 741: October 30, 21:00 UTC-4

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By Radewoosh, history, 10 hours ago, In English,

Hello, codeforces!

Sorry for the long break, but the last weeks of holidays and the first weeks of academic year took my attention. I hope today's trick will make you forgive me. :P

I invented this trick a few years ago, but for sure I wasn't first, and some of you already know it. Let's consider the following interactive task. There are n (1 ≤ n ≤ 105) hidden integers ai, each of them from range [1, 1018]. You are allowed to ask at most 103000 queries. In one query you can choose two integers x and y (1 ≤ x ≤ n, 1 ≤ y ≤ 1018) and ask a question ''Is ax ≥ y?'' The task is to find the value of the greatest element in the hidden array. The checker isn't adaptive.

Unfortunately, this task is only theoretical, and you cannot solve it anywhere, but it'll turn out, that solution can be handy in many other, much more complicated problems.

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By MikeMirzayanov, 45 hours ago, translation, In English,

Hello!

ACM-ICPC Southern Subregional Contest (NEERC/Northern Eurasia) 2018 has ended on October 16. There were 72 teams onsite in Saratov, most of them were invited because of their result on the qualification stage.

On Oct/20/2018 11:05 (Moscow time) will start online-mirror 2018-2019 ICPC, NEERC, Southern Subregional Contest (Online Mirror, ACM-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 ACM-ICPC teams and individual participants of Codeforces competitions to take part! Sure, the contest will be unrated.

MikeMirzayanov

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By isaf27, 4 days ago, translation, In English,

Hi all!

I'm happy to welcome you at the Div.1 and Div.2 shared rated round Mail.Ru Cup 2018 Round 1, it will start at Oct/18/2018 19:35 (Moscow time). The problems were prepared by me — Ivan Safonov. I'd like to thank Dmitry _kun_ Sayutin for an idea and preparation of one of the problems and Egor I_love_isaf27 Gorbachev for an idea for another one.

This round is the first round if the new championship called Mail.Ru Cup, you can learn more about it following the link. The round will be rated for everybody!

The championship feature the following prizes:

  • First place — Apple MacBook Air
  • Second and third place — Apple iPad
  • Fourth, fifth, sixth places — Samsung Gear S3
  • Traditionally, the top 100 championship participants will get cool T-shirts!

In each round, top 100 participants get prize points according to the table. The championship's result of a participant is the sum of the two largest results he gets on the three rounds.

Huge thanks to Grigory gritukan Reznikov and Ilya izban Zban for testing the problems, to Nikolay KAN Kalinin and Ildar 300iq Gainullin for their help in preparation, and to Mike MikeMirzayanov Mirzayanov for Codeforces and Polygon platforms.

The round will feature eight problems to solve in two and a half hours. The scoring will be announced closer to the beginning of the round.

I hope everyone will find some problems interesting. I wish everybody a successful round and a positive rating change!

Good luck!

UPD1,Scoring distribution:

500 750 1250 1500 2000 2250 3000 4000

Congratulations to the winners of Round 1!

  1. mnbvmar
  2. Um_nik
  3. V--o_o--V
  4. LHiC
  5. lewin

UPD2

Editorial

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Announcement of Mail.Ru Cup 2018 Round 1
 
 
 
 
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By bmerry, history, 3 days ago, In English,

I've been thinking of retiring from algorithm contests for a while, having failed to qualify for any on-sites in 2017 or 2018 (I'm excluding DCJ from algorithm contests). This is definitely a young person's game and I can feel I'm not as sharp as I used to be. I still love problem solving, but when I'm under time pressure and just can't see the solution and know my rating is going to crash, I get so stressed and frustrated that I don't enjoy it any more.

Now that both my Topcoder and Codeforces ratings are back over 3000 I've decided to retire from rated contests so that I'll go out on a high. I will most likely continue to do unrated contests where if I have a bad day I can just walk away instead of stressing myself out. I might also get more involved in testing contests.

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

"Everything is possible in ICPC as long as the community decides it should happen" — Bill Poucher.

Hello, community. I want to share my story about how our team got accepted to SEERC(Southeastern Europe Regional Contest) a couple of months ago and suddenly got declined a week ago(our registration was cancelled). I also want to ask some questions.

A little bit about regionals in Ukraine:

There are 2 stages before advancing to SEERC:

  1. First stage is held in April(almost in the end of academic year) and all the teams from Ukraine have to attend to this stage in order to go to SEERC(there are also some exceptions)

  2. Second stage is held in September(in the start of academic year)

There are also many "rules" for that stages, that are not mentioned anywhere in the official icpc.baylor.edu site.

That already doesn't make any sense because some students entering the university at the start of academic year will not be able to compete in current season, because they weren't participating in April. For example most countries can attend to SEERC without any stages before it.

Organization of first and second stage:

  1. First stage is going simultaneously in 20+ different places in Ukraine for the same problemset. There is no any organization at all. Contest can be scheduled to start at 10AM and can start in 11AM. Teams from some places in Ukraine can get statements/login/passwords at 10AM, some of them can get statements/login/passwords at 11AM, although there is only one leaderboard for all the teams from Ukraine. There are always issues with judging system during 1st stage. Almost every year there are some issues like check failed, incorrect constraints, invalid test cases and so on. Most of the problems in the problemset for 1st stage are used from internet. Almost none of them are original.

  2. Same issues are applied for second stage, but second stage is going in 5 different places and there is a bit lower percentage of problems from the internet and a bit lower percentage of issues like check failed, incorrect constraints, invalid test cases. Problemset of second stage usually contains 10-15 problems and 75% of them has difficulty  ≤  div2D. And it's always enough to solve this 75% to advance to SEERC.

The part of my story:

This year in July I was invited to enter Lviv National University and enter team to participate in ACM. One of the members of the team was competing in Finals(April 15 — April 20) this year and our first stage before SEERC for season 2019 was held in April 21(amazing, isn't it?). So he was not able to attend this stage because the ticket to Ukraine was booked for April 20 long ago and there was no way he could be in time. That's why he was allowed to create a new team that can attend to second stage or to SEERC. So I was invited to this team and one more person was taken. Here is our team: https://codeforces.com/team/46799. That's when all this started.

Ukrainian regional director didn't want to accept third member of our team, because he was marked as reserve for another team, that participated in the first stage(it wouldn't happen, if we hadn't that nonsense with stages). He didn't allow our team to participate in second stage with third member, but we had no another options. Regional director even supposed(or joked, I don't know) for us "to take pretty girl as third member, if we have no options".

So our coach decided to get in touch with regional director of SEERC and ask him if it's possible for our team to attend to SEERC. Regional director accepted our team then(it was in July). He said that there will be no problems with it. I relocated to Lviv from my home city and started team trainings. Also I entered Lviv National University in September. We trained for almost 3 months and here we got an information, that our team registration is suddenly rejected.

It appeared, that our ukrainian director wrote to SEERC regional director and him to reject our team registration, because our team was not accepted to stage 2 of ukrainian contest(because of stupid restriction for the third member that would not happen at all if there would be no that nonsense stages). SEERC regional director could still accept our team but he decided to avoid conflict with our ukrainian director and just rejected our team registration. And the point that we wasted 3 months of our time and a lot of resources to train as a team and that we wouldn't do that if he rejected our team registration at July was not an argument for him.

After that I wrote to Bill Poucher with describing this story and asking "Why did it happen?" and just got redirected to some kind of executive manager. And after some talking with him he just finally said to me(it's a quote from the letter): this tough decision is well founded by the regional leadership. I fully understand this is not what you hoped for, but the error is at the level of Lviv teams management. I understood then that it's pointless to talk with them.

I am posting it only after SEERC, because probably they can find a reason to disqualify another teams from our university and I don't really want this to happen.

So the questions are:

  1. Why did it happen? It really doesn't make sense that we got approved for SEERC and rejected 2-3 months later.

  2. Did somebody have similar problems in ACM? I already saw posts about ACPC multiple times and posts about IOI with similar nonsense situations. It's really sad that something like that happens.

  3. Is it possible to deal with this problem? Can our team somehow be transferred to another region?

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By Errichto, 15 hours ago, In English,

If you use Facebook, you might want to check out my new page https://www.facebook.com/errichto. I will post some short problems, puzzles I know/heard (maybe also not-algo puzzles, who knows), mention upcoming contests or cool problems from recent ones, sometimes share my thoughts about an algorithm or a contest. Kind of a blog, but likely with shorter but more frequent posts. Cheers!

PS. next Competitive Programming stream will be on Monday, div2 C-D problems from recent CF rounds, 12pm CEST.

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By ko_osaga, history, 16 hours ago, In English,

http://hsin.hr/coci

40 minutes left. Enjoy!

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By KAN, 16 hours ago, translation, In English,

Hi all!

This weekend, at Oct/21/2018 11:05 (Moscow time) we will hold Codeforces Round 517. It is based on problems of Technocup 2019 Elimination Round 2 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 round authors are Kostroma, Golovanov399, komendart, Denisson and Dashk0.

Have fun!

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By isaf27, history, 2 days ago, translation, In English,

Problems A-G have been created by isaf27. The idea of the problem A has been offered by i_love_isaf27.

The problem H has been created by _kun_.

Tutorial is loading...

Jury's solution: 44522356

Tutorial is loading...
Jury's solution: 44522430
Tutorial is loading...
Jury's solution: 44522470
Tutorial is loading...
Jury's solution: 44522488
Tutorial is loading...
Jury's solution: 44522506
Tutorial is loading...
Jury's solution: 44522527
Tutorial is loading...
Jury's solution: 44522542

Solution by Endagorion: 44519413 (maximal spanning tree)

Tutorial is loading...
Jury's solution: 44522571

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