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?

方法一：

class Solution {
public:
    bool isPowerOfFour(int num) {
        double result =  log10(num) / log10(4);
        return (result-int(result)==0)?true:false;
    }
};

方法二：

class Solution {
public:
    bool isPowerOfFour(int num) {
       return (num > 0) && ((num & (num - 1)) == 0) && ((num - 1) % 3 == 0);

    }
};