atcoder_official's blog

AtCoder Regular Contest 197 (Div. 2) Announcement
By atcoder_official, history, 12 months ago, In English

We will hold AtCoder Regular Contest 197 (Div. 2).

The point values will be 400-500-600-700-800.

We are looking forward to your participation!

  • Vote: I like it
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12 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

Is it recommended for a 700 rated coder in atcoder?

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    12 months ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it -19 Vote: I do not like it

    What are u saying? I think it is obvious that if your rating is below 1200, you can't get rated(which means it is not recommended for a coder with rating below 1200 to take part in it).

    Also, if a 700-rated coder can be rated in ARC, he/she can get a performance of about 1000 without solving any problems.

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12 months ago, hide # |
 
Vote: I like it +11 Vote: I do not like it

MY First Time for ARC lol

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12 months ago, hide # |
 
Vote: I like it +13 Vote: I do not like it

C seems too easy for ARC

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12 months ago, hide # |
← Rev. 3  
Vote: I like it +5 Vote: I do not like it

I solved 4 problems and my rating rose to up 1900. Problems not bad.

update: I left the contest after got AC in D and didn't find that E's answer is a polynomial that can be solved by Gauss elimination. Haha, I need to improve my observation skills.

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12 months ago, hide # |
← Rev. 2  
Vote: I like it 0 Vote: I do not like it

In the editorial for the problem B the time complexity is wrong (typo) there is $$$O(H + W)$$$, instead of $$$O(n \log n)$$$.

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    12 months ago, hide # ^ |
     
    Vote: I like it +10 Vote: I do not like it

    Thank you! It seems there was a mistake by the translator. I've corrected it.

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12 months ago, hide # |
 
Vote: I like it +18 Vote: I do not like it

For the last problem you can make a guess that the answer is a multivariate polynomial (however the degree is big, so I don't think that somebody have done it during the round). Then you can write a full bruteforce in $$$O(H^4W^4)$$$ for small cases, generate data and then do a Gaussian elimination to find the coefficients: https://atcoder.jp/contests/arc197/submissions/65514178. Took me 3-5 mins to generate, but if you know the true degree, it will be less than 1 min.

  • My question to smarter people is how to find the minimal number of inputs and their values ($$$n, h, w$$$ or in a general multivariate case) to guarantee the answer (the system has exactly 1 solution)?
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12 months ago, hide # |
← Rev. 2  
Vote: I like it 0 Vote: I do not like it

For B just this "We can swap a big number with smaller number" is sufficient. This will prove that the best case will always be some prefix of the sorted array.

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    12 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    My proof might be simplifiable. However, I think the statement "We can swap a big number with a smaller number" is incorrect. For example, changing [1,1,2,2,2] to [1,1,1,2,2] decreases the score.

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12 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

This maybe the easiest ARC I've ever participated. It maybe great for both the grands and me.

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12 months ago, hide # |
← Rev. 2  
Vote: I like it -25 Vote: I do not like it

I think the current Rating system is a bit unreasonable. For those who don't have AC problems at contests, Rating should stay the same, or else change the rating score based on Perf. Take this ARC as an example, some people (like me) with a Rating less than 1200 had an over-performance, AC two problems, and reached a Perf of 1400, but this had no effect on their Rating, which I think is unfair, and I hope that the AtCoder officials will respond to this.

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    12 months ago, hide # ^ |
    ← Rev. 2  
    Vote: I like it 0 Vote: I do not like it

    I object. The ARC rule states that people below 1200Rating are not rated. If people below 1200Rating are rated, the minimum Perf will be lower, and other rating calculations will be confused.

    Perf is calculated by the rated people's rating I think, so you got 1400Perf don't means you can get 1400Perf if all the 1200Rating- people Rated register.

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      12 months ago, hide # ^ |
      ← Rev. 3  
      Vote: I like it -31 Vote: I do not like it

      You have a point, but AtCoder could have just automatically Unrate users who were Rated and didn't have AC problems after the contest, and then gone ahead and settled the Ratings, which I think would have been better.

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        12 months ago, hide # ^ |
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        Vote: I like it 0 Vote: I do not like it

        AtCoder could have just automatically Unrate users who were Rated and didn't have AC problems after the contest

        I disagree, too.

        if somebody know that he will get positive delta if he solves $$$x$$$ problems but will not if he solves $$$x-1$$$. He can see the $$$x$$$-th problem first, then choose to be automatically Unrated or take the contest.

        In short, I think the current AtCoder Rating Rule is the best.

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