题目链接：https://leetcode-cn.com/problems/recursive-mulitply-lcci/
题目如下：

class Solution {
public:
    int multiply(int A, int B) {
        //n个k相加=(n/2个k相加)+(n/2个k相加)+0(或k)
        int n=A;//min(A,B);
        int k=B;//max(A,B);

        if(n==1) return k;
        int half=multiply(n/2,k);

        if(n%2==1) return half+half+k;
        else return half+half;
    }
};