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?

Credits:

这道题让我们判断一个数是否为4的次方数，那么最直接的方法就是不停的除以4，看最终结果是否为1，参见代码如下：

解法一：

class Solution { public: bool isPowerOfFour(int num) { while (num && (num % 4 == 0)) { num /= 4; } return num == 1; } };

还有一种方法是跟Power of Three中的解法三一样，使用换底公式来做，讲解请参见之前那篇博客：

解法二：