LeetCode OJ——Unique Binary Search Trees

class Solution {
public:
    int numTrees(int n) {
        if(!n||n==1)return 1;


        vector<int> numVector;
        numVector.assign(n+1,0);
        numVector[0]=1;
        numVector[1]=1;

        for(int i=2;i<=n;++i)
        {
            for(int j=0;j<=i-1;++j)
            {
                numVector[i]+=numVector[j]*numVector[i-1-j];
            }
        }

        return numVector[n];
    }
};