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