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
;
delete []num;
return temp;
}
};