I wrote kd-tree based solution but still TL#16, and I cannot find bad cases for my realization (on my local machine it finishes within 1 sec on any test). Any ideas of what kind of tests may these be?

Edited by author 26.03.2013 04:00

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According http://codeforces.ru/blog/entry/7029#comment-128560, sweet pieces are located very close to each other. Cockroachs are located around them uniformly. But this is in test 17 (as written in comment).