ipaljak's blog

Croatian Open Competition in Informatics (COCI) 2019/2020 — Round #1
By ipaljak, history, 5 years ago, In English

Hi all,

it's the most wonderful time of the year as the new season of COCI is getting near :)

Join us on the first round which will be held on Saturday, October 19th at 14:00 UTC.

If you are not familiar with COCI contest format, we encourage you to read the announcement for the new season. Also, this year we have decided to allocate the same number of points to the three hardest tasks and present them in lexicographical order in the problemset.

Feel free to discuss the problems here after the contest ends.

See you on Saturday!

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Comments Comments (28)
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5 years ago, # |
  Vote: I like it +32 Vote: I do not like it

COCI is love COCI is life

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5 years ago, # |
← Rev. 2   Vote: I like it +42 Vote: I do not like it

I found that all contest held in last year had no "solution"s (that is, editorials are not uploaded).

How is it going this year?

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    5 years ago, # ^ |
      Vote: I like it +24 Vote: I do not like it

    Yeah, we had quite a few complaints about that. We'll give our best to publish this year's editorials on the same day when the round is held.

    Regarding the editorials from the last two seasons, I hope we'll manage to finish and publish all of them during this season.

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5 years ago, # |
  Vote: I like it +18 Vote: I do not like it

Friendly reminder: the round starts in about 4 hours.

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4 years ago, # |
  Vote: I like it +36 Vote: I do not like it

So, what do you think about the round and new format of scoring? :)

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    4 years ago, # ^ |
      Vote: I like it +20 Vote: I do not like it

    I think 90 < 110 < 130 is much better because I want some diversity in difficulty. On the other hand, the new subtask system is awesome, and I like the PDF format too.

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      4 years ago, # ^ |
        Vote: I like it +26 Vote: I do not like it

      They were meant to be diverse in difficulty. We assumed zoo < trobojnica < dzumbus. The idea behind the same score was to train our contestants to sniff out the easy tasks since they need that skill for IOI.

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        4 years ago, # ^ |
          Vote: I like it +49 Vote: I do not like it

        I trained a lot with COCI, so phrases like "COCI p5 difficulty" are quite idiomatic to me. Time for a change :)

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          4 years ago, # ^ |
            Vote: I like it +16 Vote: I do not like it

          Really cool to hear the so called "HONI" (COCI) ranking is used by non-Croats. <3

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4 years ago, # |
← Rev. 2   Vote: I like it +23 Vote: I do not like it

Nice contest! I solved a problem identical to the last problem before.

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    4 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    One person also mentioned that as a clarification request. He said the same problem was used in Iranian IOI training.

    I actually suggested that problem to be included in last year's COI (which is more important for us than a regular COCI round), but we thought it was too easy and rejected it :)

    I'm sorry if it was a well-known problem for a lot of competitors, but none of us from the scientific committee saw it before and it looks like our competitors didn't know about it either.

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      4 years ago, # ^ |
      ← Rev. 3   Vote: I like it +18 Vote: I do not like it

      I don't mind it, i find the problem very interesting. Btw. will we be able to submit codes again (I wanna know why my B failed)?

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        4 years ago, # ^ |
          Vote: I like it +8 Vote: I do not like it

        I will try to make that happen. We had some attacks during analysis mode last season so our technical staff is reluctant to allow it this year.

        I'll let you know when/if it happens.

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          4 years ago, # ^ |
            Vote: I like it +10 Vote: I do not like it

          The analysis mode is up and running.

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4 years ago, # |
  Vote: I like it +31 Vote: I do not like it

The expected solution of dzumbus is $$$O(N^3)$$$ or $$$O(N^2)$$$?

By the way, problem trobojnica was very nice.

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    4 years ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    $$$O(N ^ 2)$$$ is the official solution. Did you pass a $$$O(N ^ 3)$$$ solution or maybe you think it is a $$$O(N ^ 3)$$$ solution :D. The proof of complexity is a key part of the solution.

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      4 years ago, # ^ |
        Vote: I like it +10 Vote: I do not like it

      I am pretty sure that the worst case of my solution is $$$O(N^3)$$$ but it takes full score (with maximum time = 0.06s). Either the testcases are weak or it's simply impossible to distinguish between the quadratic solution and a cubic solution with a very small constant when $$$N=1000$$$.

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    4 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    It was O(n^2). The editorial should be up very soon.

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    4 years ago, # ^ |
      Vote: I like it +33 Vote: I do not like it

    Thanks! Do I get extra credit in Figalli's class for it? :D

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4 years ago, # |
  Vote: I like it +31 Vote: I do not like it

You can see the results and solutions (with editorial) here.

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    4 years ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    Some take hours, some take years ... :D

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    4 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    When I try to download the tasks I get "403 Forbidden".

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4 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

You can submit all problems except Trobojnica here: https://oj.uz/problems/source/442

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it +8 Vote: I do not like it

    You can take code for checker of Trobojnica from the solution of task Checker from round 2.

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      4 years ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      Nice, now all problems are available, thanks :D

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