Shtrix's blog

CodeForces Beta Round #15
By Shtrix, 14 years ago, translation, In English

Greetings, CodeForces users. CodeForces Beta Round #15 will be held today, 29th of May at 19:00 MSK. My name is Roman Iedmeksyi and I am lucky to introduce this problem set.

I would like to thank Dmitry Matov, Julia Satushina and Mike Mirzayanov for well-coordinated work on this match. Also I would like to mention the contribution of Yaroslav Tverdokhlib in problems testing.

Some information about me:       

I am a student of Kyiv National Taras Shevchenko University. I started programming at school. As my first achievement I had taken third place in Ukrainian Olympiad in Informatics. Next year I’ve worked harder and was qualified to IOI 2009 selection. Unfortunately I had not enough experience to pass.

In this contest I wish you good luck and high results.

UPD contest extended by 15 minutes

UPD Codeforces team apologizes that during today's round the server was regularly unavailable due to different technical reasons. We will try to do our best to avoid similar situations on the upcoming contests. Our apologies for some mistakes in the statements. Because of these reasons today's competition results will not affect your rating.

Looking forward to seeing you at Codeforces Beta Round 16.

Announcement of Codeforces Beta Round 15
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  • Vote: I do not like it

Comments Comments (17)
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14 years ago, # |
  Vote: I like it +4 Vote: I do not like it
Could you please mirror the problem statements somewhere? I'm still having trouble with viewing problem D.
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14 years ago, # |
  Vote: I like it +4 Vote: I do not like it
Anyone having trouble connecting to CodeForces during the match?  My keep getting cut off from the site.
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14 years ago, # |
  Vote: I like it +2 Vote: I do not like it
Same here. I hope the contest isn't rated. Couldn't read or submit problems.
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14 years ago, # |
  Vote: I like it 0 Vote: I do not like it
Is it possible to publish a simulation of the rating change?
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14 years ago, # |
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How the problem C can be solved?
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  • 14 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it
    First you need to know the Nim game theory, http://en.wikipedia.org/wiki/Nim

    Resuming, you just do the xor of the heights of all towers (nimsum) and check if its equal to zero.
    As you have so many towers you can't do this one by one.

    If you analise the nimsum sequence from 0 to N, you'll notice that all multiples of 4 have the nimsum value equal to the number. So just iterate from the nearest multiple of 4 till N

    One property of the xor is that AxorBxorB = A.

    So if you want the NimSum [A..B], you do NimSum[0...A-1]xorNimSum[0...B]
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    • 14 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it
      Could you explain, why    NimSum[A..B]= NimSum[0..A-1] xor NimSum[0..B].
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14 years ago, # |
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Not able to view submitted solutions of others for beta round #15. Anyone else facing same problem?
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  • 14 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    Yes. Maybe submitted solutions will be opened later.
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14 years ago, # |
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When the rating will be updated ?
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14 years ago, # |
  Vote: I like it +6 Vote: I do not like it
Sorry. Next time i will read before posting.
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