Errichto's blog

SRM664 Editorial
By Errichto, 9 years ago, In English

You can find editorial here. Sorry for technical troubles with challenging. What do you think about problems? Which did you enjoy, which do you hate?

--UPDATE--

broadcast: The match will be rated, and challenge results will stand. However, if you feel you were personally affected negatively/unfairly, please message [email protected], and I will consider individual requests. (I have some limited ability to confirm that individuals had issues)

  • Vote: I like it
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  • Vote: I do not like it

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9 years ago, # |
  Vote: I like it +7 Vote: I do not like it

I can't login to topcoder

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9 years ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

Just in case admin did not read through chat:

There are at least me & fushar will be affected if the challenge phase is nullified: We used so much time in coding phase to create good challenge test. I think since D1 250 is not so easy to create challenge test, many other people may also be affected by this.

So if you decide to nullify challenge phase, please also consider making round unrated.

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    9 years ago, # ^ |
    ← Rev. 8   Vote: I like it +21 Vote: I do not like it

    I just used the following test for challenge case (which is not too hard to come up with?)

    (7, 109, 2·109). This works because the whole problem boils down to 2a ≡ 1( mod A + B) for some a (at least in brute force cycling solutions).

    Then 109 + 7 is great because the order of 2 is at least 5·108 + 3 (since this is prime too).

    Just a note: I will not get 100 and potentially even more if challenge is nullified. I was just giving this test case to everyone that was not doing binary pow, and if challenge phase was fast I would get many points for this. I predict that the issue was that the challenge cases were all causing TLE which can be annoying for the judge.

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

      I wanted to challenge solutions that calculate length of cycle of the transformation. It is not obvious to me how to easily create a test that has large cycle length.

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    9 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Both possible decisions (rated/unrated) aren't perfect. Sorry that it happened. We will try to choose the best option.

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    9 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I made a (probably?) good challenge test by throwing some powers of 2 to some numbers. The GCD is 1 and the sequence doesn't have a small period, so it should kill a lot of simulate-till-x solutions.

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9 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by Errichto (previous revision, new revision, compare).

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9 years ago, # |
  Vote: I like it +13 Vote: I do not like it

I liked the way how author avoided using float numbers in problem 550 div1 :)

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

    Thanks. Otherwise, it would be enough to consider very short paths.

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      9 years ago, # ^ |
        Vote: I like it +7 Vote: I do not like it

      Yeah, indeed preety clever. However there is also a second solution to problem of short paths which is giving float probabilites (almost) equal to 1 to nodes, however I prefer one you've chosen.

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9 years ago, # |
  Vote: I like it 0 Vote: I do not like it

when i try to open the editorial from the link provided login request prompts. when i feed my details it shows system error. some help needed. thanks

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    9 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Go to main Tc website, login there and try my link again

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9 years ago, # |
  Vote: I like it +3 Vote: I do not like it

Nice problems Errichto!

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

I faced problem in challenge. This solution passed for Div2B, I think its fail for testcase(498,480,483).And This solution got uncaught exeption, I think its for large memory , but it works fine my compiler.

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