LeetCode-342：Power of Four

This is another "Pick One" Problem ：【Problem：342-Power of Four】

Given an integer (signed  bits), write a function to check whether it is a power of .

Example:

Given num = , return true. Given num = , 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.

巴特西

LeetCode-342：Power of Four

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