96. Unique Binary Search Trees

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