Saturday, February 21, 2009

Screencasts since fall

This will probably only be interesting for TopCoder players, and they've probably already seen this on the forum, but anyway. Here're the screencasts for the SRMs that happened since my next-to-last post.

With problems not being very difficult, all came down to the challenge phase, and I was lucky to emerge in the 1st place in the end :) There was nothing particularly interesting about my challenges - I've had a pre-crafted case for the medium where I felt many can hit integer overflow, but only found one solution to challenge with it; and I've found a timeout case for a backtracking solution in the hard.

Nothing exceptional except stupid switch to C++ to use upper_bound that costed me quite a lot of time and points instead of just using binary search :)

This SRM highlights one of the techniques that I believe has improved my TopCoder results quite a bit - doing a stress-test against a stupid solution on random testcases. I've managed to resubmit the hard problem correctly because of it.

SRM 433 - no screencast - but just a comment.
Wasn't it stupid to do a last-second challenge on a possible hash collision when I was in first place with less than 25 points of margin? Yes it was.

With problems that seemed to suit me and a late resubmission by ACRush, there was no need in much challenge activity. And since I've chosen the wrong problem to challenge (who would've thought of so many ways to fail the easy? :)), the screencast should be rather boring in the challenge phase.

Very nice problems, but too slow thinking at 5AM. And very thorough example cases.


  1. Hi Petr,

    Have you come across any TopCoder problem that you couldn't solve? (I mean not only in competitions but also in practice rooms). I found that you have compiled the SRM 331 DIV 2 250 problem but have not submitted it. Is it because you couldn't solve that problem, or you didn't bother submitting it because it is too easy?

  2. Most probably I was just testing that my plugins were set up correctly.

    Of course I have come across quite a few TopCoder problems that I couldn't solve given the time constraints. There were a few problem where I've asked a friend about the solution after the contest instead of inventing it myself, so I didn't solve those problems at all in a sense :)

  3. Whar a software did you use to record the screencasts ?