can someone explain how to do this problem http://codeforces.com/contest/134/problem/B
i used dfs that resulted in TLE, number theory tag is given at hints, but i am not able to understand how to do it ?
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read about Euclidean algorithm.
when you go forward, from any vertex (a, b) you can go into 2 other vertices: (a, a + b) or (a + b, b), but when you go backward at any step there is only one vertex to move in: (a, b - a) if b > a, or (a - b, b) if a > b
so, solution is simple bruteforce, and it works fast.