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?

思路：

可以沿用求3的幂次中的思路，验证log₄N是否为整数来判断。

解法：

 1 public class Solution 2 { 3     public boolean isPowerOfFour(int num) 4     { 5         double n = Math.log10(num) / Math.log10(4); 6  7         if(n == (int)n) 8             return true; 9         else10             return false;11     }12 }

LeetCode 342 Power of Four