Unique Binary Search Trees
Given n, how many structurally unique BST's (binary search trees) that store values 1...n?
For example,
Given n = 3, there are a total of 5 unique BST's.
1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3
class Solution { public: int numTrees(int n) { if(n==0 || n==1) return 1; int sum=0; for(int i=1;i<=n;i++) sum=sum+numTrees(i-1)*numTrees(n-i); return sum; } };