LeetCode 342. Power of Four（4的n次幂）

原题网址：342. Power of Four 342. Power of Four 342. Power of Four 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：判断是否只有个1个比特为1，并且1后面有偶数个0。

public class Solution {
public boolean isPowerOfFour(int num) {
return num > 0 && (num & -num) == num && (num & 0x55555555) != 0;
}
}

另一种实现：

public class Solution {
public boolean isPowerOfFour(int num) {
return num > 0 && (num & -num) == num && (num & 0x2AAAAAAA) == 0;
}
}