At the moment my way is to look through all the squares of length LEN (using binary search) and to check, whether a hash of a square was met before. It is of O(N*M*log(min{N, M})) complexity.
But I get WA#10 again and again. Please, if someone had a problem with this test, share your impressions, 'cause I'm going slightly mad.

You have a collisions with hash. (I've got this problem also because second number x was to small and close to first one).

Thank you, it really had to do with collisions. Actually, my self-made hashset implementation was fantastically awful. :-)

Edited by author 06.07.2012 15:48

Why you have used binary search? How we can say that the sq. matrix 2x2 has less value than 3x3. and 3x3 has less than 4x4. how can we justify?