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?

题意：给定一个整数，写一个方法来判断这个数是否为4的次幂

思路：一开始没看到下面的要求是尽量不用循环和递归，于是用循环写了一个，很简单，一直除4，知道最后值为1，则为true， 否则为false

class Solution {    public boolean isPowerOfFour(int num) {        if(num<=0){            return false;        }        if(num == 1){            return true;        }        while(num%4==0){            if(num/4==1){                return true;            }else{                num = num/4;            }        }        return false;    }}