Nope, it is at least O(M*N*log(N) + N^3), but with N~50 it is not noticeable.

For each tower check how many towers can be skipped, that is for each possible skipping length check if there are monuments ccw to the chord: O(M*N^2), but can be O(M*N*log(N)) with binary search.

For each length and each start calculate minimal perimeter on the way from start to start+length trying all intermediary towers: O(N^3).

For each triple of towers that form a triangle, sum minimal perimeters and find the global minimum: O(N^3).

Edited by author 13.05.2014 12:53

So many happy people there), but I still wa4 :P
Will someone ACer put here correct answer for this test?
13 3
-5 3
-3 6
0 7
4 6
7 5
7 4
7 3
7 2
5 -3
4 -3
3 -3
-2 -3
-5 -2
3 3
5 0
-1 1
My prog says 30.20