Comment on Codeforces Round #499 -- interactive problem

Revision en6, by cdkrot, 2018-07-26 20:50:59

Unfortunately, we had a bug in our interactor of the interactive problem.

The interactor contains the following code:

if (y < x)
    t = -1;
else if(y > x)
    t = 1;
    t = 0;
if(!p[q % n])
    t *= -1;
cout << t << "\n" << flush;

This is the opposite to the statement. However, it turns out that this error doesn't causes any harm for solving problem — it actualy just inverts the pattern, selected by judges. This also wasn't noticed during testing, by the same reason — the error is not visible to the user code.

But it may cause unexpected behaviour for hackers -- since they write the pattern themselves.

We are very sorry for this error and decided to do the following:

  • The round will be rated, because very little people (maybe even zero) got affected (the people, who made incorrect hack)
  • If you made a hack, which turned to be incorrect due to the error, we will cancel your  - 50 points and recalculate your rating afterwards. Please PM me if you have such a hack.

We are very sorry again. This is a huge lesson to us to be more attentive.

I hope you enjoyed the round!


  Rev. Lang. By When Δ Comment
en6 English cdkrot 2018-07-26 20:50:59 18 Tiny change: 'le people got affec' -> 'le people (maybe even zero) got affec'
en5 English cdkrot 2018-07-26 20:43:19 6
en4 English cdkrot 2018-07-26 20:41:14 2
en3 English cdkrot 2018-07-26 20:40:52 24
en2 English cdkrot 2018-07-26 20:39:57 29
en1 English cdkrot 2018-07-26 20:38:18 1226 Initial revision (published)