LeetCode 342. Power of Four

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

先说明用循环：

如下

class Solution {
public:
    bool isPowerOfFour(int num) {
        if(num<1)return false;
        char position=-1;
        int i=0;
        while(i<=31)
        {
            if(num&(1<<(i)))
            {
                if(-1!=position&&position!=i)
                return false;
                position=i;
            }
            ++i;
        }
        if(position%2)return false;
        else return true;
    }
};

然后我发现题目中提示，你可以不用循环或者递归吗？我就去搜寻了一下这个题目发现http://www.cnblogs.com/grandyang/p/5403783.html

发现第三种方法很巧妙