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  • 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.

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  • 原文地址:https://www.cnblogs.com/shenxiaolin/p/8338073.html
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