SecondThread's blog

Meta Hacker Cup Round 3
By SecondThread, history, 5 hours ago, In English

Meta Hacker Cup Round 3

Round 3 is upon us! Round 3 begins in under 24 hours on the Hacker Cup site. We hope to see you there after Round 984!

As in previous years:

  • To qualify for the human track of Round 3, you must have finished within the top 500 of Round 2.
  • To qualify for the Finals Round, you must have finished within the top 25 of Round 3.
  • For those competing in the human track, the top 200 placing participants have a special badge on their shirt.

Good morning, have fun, and we hope to see you on the scoreboard! Head on over after Codeforces Round 979, and be careful not to make any algorithms mistakes!

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5 hours ago, # |
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That's fantastic! I think it will be funny.

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

Has T-shirts for round 2 been released yet?

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

What about the T-shirts for the top 2000 in round 2??

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    90 minutes ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Top 2k in round 2 will get shirts, they just won't have a "Top 200" badge on them.

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4 hours ago, # |
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Well I guess time travel is possible nowadays.

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98 minutes ago, # |
  Vote: I like it +50 Vote: I do not like it

Problem E is one of the best joke statements I've seen. A brilliant idea to use the name of Dijkstra!

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    90 minutes ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    I'm glad you like it :)

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    85 minutes ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    Agreed! Though I am confused why anyone went for E2 given its point value.

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      77 minutes ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      The contest organizers had some interesting thoughts about E's value and strategy. If the set is easy and likely to get solved, it would make a lot of sense to do E1/E2, that way your penalty gets significantly improved.

      But if solving the set isn't important, then going after E instead of C or D wouldn't be too helpful; because of the double penalty. It's an interesting call you have to make early on in the contest.

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

        Makes sense. I reasoned after finishing E1 that I almost certainly wouldn't have the time to finish everything, so I ended up going for the larger point values.

        Though I still think it's a bit strange how C = D = E1 + E2; IMO E1 + E2 should be worth more.

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97 minutes ago, # |
  Vote: I like it +17 Vote: I do not like it

FST fiesta incoming, A's validation cases don't check $$$k = 3$$$ and E1 has $$$5$$$ validation cases for a YES / NO problem lol (where I'm pretty sure 3 are the direct samples).

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88 minutes ago, # |
  Vote: I like it +9 Vote: I do not like it

Thanks for the weak pretest, I thought I wasn't gonna get a top 200 this year xdd

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85 minutes ago, # |
  Vote: I like it +15 Vote: I do not like it

After the contest I felt quite happy, as I had enjoyed competing. Then I looked at the scoreboard.

In any case, thanks to the organizers!

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85 minutes ago, # |
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So are weak pretests in MHC now going to become a thing? Asking for the next year and future version.

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    77 minutes ago, # ^ |
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    There is a reason why they say validation input rather than pretests.
    These tests exist to just ensure one's output file format is correct.

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83 minutes ago, # |
  Vote: I like it +3 Vote: I do not like it

Solved D 12 minutes after the contest ended...

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

Good news: I didn't failed system test this time.

Bad news: I only solve problem A. (And FST only make my ranking drop from 296 to 303)

So saddddd.

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    65 minutes ago, # ^ |
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    I FSTed both A and E1, and my B code RTEd on main tests. gg

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68 minutes ago, # |
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What manually submitting 50+ submissions for B did to my Downloads folder

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65 minutes ago, # |
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I was doing so well on C until Wolfram Alpha told me to use a digamma function ... Tragic.

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65 minutes ago, # |
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Are all the correct and incorrect results true now (except for the penalty calculation) ?

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    61 minute(s) ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    They are correct, and penalty is correct. We might DQ some people for plagiarism, but usually there's not too much of that.

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      59 minutes ago, # ^ |
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      Thank you for your prompt reply!

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64 minutes ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

Ah, I solved B and C, but in B I stupidly did return {set, map} instead of return {move(set), move(map)}, and in C I relied on boost::math::digamma to compute the sum of $$$\frac{1}{A+Bk}$$$ over $$$k$$$ from $$$L$$$ to $$$R$$$, but it turned out to be not precise enough (produces relative error of $$$8 \cdot 10^{-6}$$$). Sadge, two avoidable things landed me 17 places away from a better t-shirt :(

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61 minute(s) ago, # |
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What is special with p=0 in problem C?

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59 minutes ago, # |
← Rev. 3   Vote: I like it +15 Vote: I do not like it

I solved E because I have read this paper: Incorrect implementations of the Floyd--Warshall algorithm give correct solutions after three repeats.

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54 minutes ago, # |
  Vote: I like it +6 Vote: I do not like it

What was the issue with B?

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    32 minutes ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    We're still looking into it. There's nothing fundamentally interesting about the I/O compared to other problems. It has a large input file, but so do other problems, and that doesn't affect uploading the output of course.

    Interestingly, the judges had no issue making any of the submissions, and it's the same mechanism under the hood for judges and contestants.

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    30 minutes ago, # ^ |
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    Idk if this only happened to me, but I had to redownload input for 5 times. After that I couldn't create submission and got repetitive error responses. (Probably, I requested too much download) Then, the timer expired and I sent my output and code to clar within a minute and they made a submission for me.

    It's weird that I could attach and send my submission in clar just fine, but not problem B.

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38 minutes ago, # |
  Vote: I like it +9 Vote: I do not like it

Thanks for the round! I was (luckily) just right about how careful I should be.

It was evident that A and E1 have "weak" validation if we download them (before solving). What was not evident for me is C's weakness (the case where you use the 100% option with large $$$N$$$). I was rescued by stress testing for all of them...

By the way my directory and my brain messed up by downloading validation inputs before solving and caring about the problem titles. Perhaps this has been raised before, but I was wondering if the organizers could attach problem ID as a prefix to input file names (like A- or E1_).

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19 minutes ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

Sad for jiangly. I wanted to see him in the finals.

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6 minutes ago, # |
  Vote: I like it +4 Vote: I do not like it

How were the "ground truth" answers found in problem C?

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