问题描述

Given an integer, write a function to determine if it is a power of two.
Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

思路分析

1. 用log函数，判断得到的指数是否约为整数。Runtime: 76 ms, which beats 5.28% of Python submissions.
2. 循换进行模2判断并右移一位。Runtime: 68 ms, which beats 13.69% of Python submissions.
3. 将十进制数转为二进制字符串，除第一位外其他位均为0则该数字是2的幂。Runtime: 56 ms, which beats 67.47% of Python submissions.

AC代码

class Solution(object):
    def isPowerOfTwo(self, n):
        if n <= 0:
            return False
        return n == 1 or not '1' in bin(n)[3:]