I was trying to solve the problem http://mirror.codeforces.com/problemset/problem/380/C .I saw Segment tree approach in the editorials.Now I was thinking Can we do it by memoization.Increasing the value +1 for every "(".Now we have two options ,Whether we should include next character to close this subsequence on not.Initially it would be exponential but by doing memoization I think we can do this.Looking to hear from you guyz?????