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
;
}
}