I've recently come across a very strange problem using C++ 11.
I submitted a solution for problem 620C - Жемчужинки using unordered_map and got TLE, then I submitted the exact same solution using map (it's supposed to be slower: O(1) amortized VS O(logN) per operation) and it got Accepted with 280 ms.
Submission with unordered_map: 15756653
Submission with map: 15759645
Is this some kind of problem with the C++11 compiler used here on Codeforces? Anyone got a clue?
Auto comment: topic has been updated by tenshi_kanade (previous revision, new revision, compare).
Looking at the different execution times, for both submissions, unordered_map seems to be faster, maybe that particular case is antihashing and a lot of collisions happen? That could explain the TLE
http://mirror.codeforces.com/blog/entry/22947?#comment-274056