My algo is O(N) and it works 0.265 s... But there are solutions which work 0.06!! How? Can anybody tell me such algo.

using dfs but own stack management

My algo is normal recursion, and I have used pointer, too.
It got AC in 0.093sec.
Maybe I change the pro into unrecursion and unpointer,it could faster...

Can anybode tell how to solve this problem?
I had TLE #13 and I don't know what to do!!!