LoneFox's blog

Facebook Hacker Cup 2020: Round 3
By LoneFox, history, 4 years ago, In English

Round 3 of the 2020 Facebook Hacker Cup is less than 48 hours away!

The round will begin on September 12th, 2020 at 10am PDT and will last for 3 hours. The contest can be found here.

You're eligible to compete in Round 3 if you were among the top 200 contestants in Round 2.

The top 25 contestants will also advance to the Final Round, which will be hosted virtually and live streamed at www.facebook.com/hackercup later this year. Please note that all submission judgments will only be revealed after the round ends, and that time penalty will be used to break score ties. More details about rules and other information can be found in the FAQ.

We wish you the best of luck, and hope that you enjoy the contest!

The Facebook post can be found here.

Update: The round has ended, thank you for participating! The scoreboard can be found here, and the solutions here.

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

Comments Comments (26)
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4 years ago, # |
  Vote: I like it +15 Vote: I do not like it

I know this is a bit random, but does anyone know when t-shirts will be delivered?

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    4 years ago, # ^ |
      Vote: I like it +23 Vote: I do not like it

    From Rd 2 post:

    We'll begin shipping out t-shirts by early 2021 or earlier, at which point the winners will receive emails with tracking information.

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

Predictions?

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4 years ago, # |
  Vote: I like it +125 Vote: I do not like it

Last time I was pretty vocal about the ugliness of problem D (of round 2).

This time, I want to say that problems B and C were very cool. For me, they were both interesting, fun to solve and with an appropriate difficulty.

Congratulations to the organizers!

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

    Thanks for the feedback! It's always good to know what people like/dislike.

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

    Agreed, really liked B.

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

    I would like to second this, problems this time were much better than in previous rounds.

    Thanks for the contest!

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4 years ago, # |
← Rev. 2   Vote: I like it +54 Vote: I do not like it

C has a similar trick as Boomerang Crews.

Edit: Even multiple tricks I guess. In both problems, you have to binary search for the result and then do the trick with pairing elements by maintaining items sorted by value modulo something.

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4 years ago, # |
  Vote: I like it +43 Vote: I do not like it

I'm kinda glad that you spent all bad problems on round 2 and left all good ones to round 3 :) I enjoyed BCD, especially B (looks like it was easier for lots of people than for me, maybe I didn't know some trick).

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4 years ago, # |
  Vote: I like it +55 Vote: I do not like it

Sysfail on B, C :( btw, problemset was far better than previous rounds. Great job!

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4 years ago, # |
  Vote: I like it +78 Vote: I do not like it

Also: I enjoyed the problems, finishing D at the end gave me that heart-pounding which we all love in CP. Thanks for the contest.

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

Thanks for the round! Seconding all the comments about the improved problem quality this round--I wasn't a huge fan of either Rounds 1 or 2, but I thought all the tasks this round were exceptionally fun to solve. The observations for D were especially nice!

I definitely did not expect to place in the top 25 this year, but I'm thrilled to have made the cut and can't wait to compete at WF later this year!

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

Is it ok that in statement of C $$$T\le 90$$$, but in the input file I got $$$T = 113$$$? Not that it affected me, my code had bugs, but this is quite suspicious. And some submissions which got AC also WA on my input file...

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

    In practice mode, T may be higher than the listed bounds because we give you the complete file.

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      4 years ago, # ^ |
        Vote: I like it +1 Vote: I do not like it

      Got it, thanks

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

      Complete file compared to what? Do you give different inputs to different participants?

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

        Samples and validation tests are included.

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

          I thought they are nested as is, I'm pretty sure that when I glance over the output file to ensure that I have run the code I always see answer for samples.

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        4 years ago, # ^ |
          Vote: I like it +11 Vote: I do not like it

        Yes, they give different input to different participants. I think the point is to discourage/detect cheating where someone submits someone else's output.

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

          That's a bit unfare, isn't it?

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

            Are you worried that the exact set of cases being different could affect runtime? I don't know the details, but I believe the random subset is selected intelligently with multiple pools based on size/shape/etc. (Also, 90/113 is pretty much all of them anyways.)

            LoneFox knows more details, I remember seeing some comment from him about this, but I can't find it now.

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

              That's right, there's only a bit of variation — everybody receives all of the large and/or "important" cases within their input file.

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4 years ago, # |
  Vote: I like it +86 Vote: I do not like it

Imagine a mailbox so small that it cannot even contain its own key lmao

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

If I got a tshirt, should I wait until the shipping to deactivate my account?

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