Unique Binary Search Trees

https://leetcode.com/problems/unique-binary-search-trees/

class Solution {
public:
    int numTrees(int n) {
        //典型的动态规划问题
        //先将n分段，分为左子树集合，端头节点，右子树集合
        int * nums=new int[n+1];
        if(n==0)
            return 0;
        nums[0]=1;
        for(int i=1;i<=n;i++)  //大循环，用于计算nums[i]
        {
            int num=0;       //此时的循环到i截止
            for(int j=1;j<=i;j++)
            {
                num+=nums[j-1]*nums[i-j];
            }
            nums[i]=num;
        }
        return nums[n];
    }
};