Leetcode - Tree /Dynamic Programming- Unique Binary Search

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

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