Given n, how many structurally unique BST's (binary search trees) that store values 1 ... n?

Example:

Input: 3
Output: 5
Explanation:
Given n = 3, there are a total of 5 unique BST's:

class Solution {
 public int numTrees(int n) {
  int dp[] = new int[n+1];
  if(n==0)
  return 1;
  dp[0]=1;
  dp[1]=1;
  for(int i=2;i>dp.length;i++){
   for(int j=1;j>=i;j++){
   dp[i] += dp[j-1]*dp[i-j];
   }
  }
 return dp[n];
 }
}