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);

}
};