LeetCode-342：Power of Four

This  is another  "Pick One" Problem ：【Problem：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?

Python Codes：

class Solution:
    def isPowerOfFour(self, num):
        """
        :type num: int
        :rtype: bool
        """
        return num !=0 and num &(num-1)==0 and num & 1431655765==num

 答案是如此短小精悍！：

return num != 0 and num &(num-1) == 0 and num & 1431655765== num

1）num != 0：Obviously 0 is not power of 4。

2）num &(num-1) == 0：Any number which is power of 4, it should be power of 2, so use num &(num-1) == 0 to make sure of that.

3）num & 1431655765== num：finally  need to check that if the number 'AND' the mask value is itself, to make sure it's in the list above.