96. Unique Binary Search Trees

public class Solution { public int numTrees(int n) { int[] res = new int[n+1]; res[0]=1; res[1]=1; for(int i = 2; i<= n; i++) { for(int j = 0; j < i; j++) { res[i] += res[j]*res[i-j-1]; } } return res[n]; } }