leetcode 342. Power of Four

题目：

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?

public class Solution {
    public boolean isPowerOfFour(int num) {
        if(num<=0)
            return false;
        int a=0x2aaaaaaa;
        if(((num&a)==0)&&((num&(num-1))==0))
        {
            return true;
        }
        return false;
    }
}