231. Power of Two

Given an integer, write a function to determine if it is a power of two.

Example 1:

Input:1

Output:true 

Explanation: 2^0 = 1

Example 2:

Input:16

Output:true

Explanation: 2^4 = 16

Example 3:

Input:218

Output:false

Thoughts:

Power of 2 means only one bit of n is '1', so use the trick n& (n-1)==0 to judge whether that is the case

class Solution(object):
    def isPowerOfTwo(self, n):
        """
        :type n: int
        :rtype: bool
        """

        return False if n<= 0 else (n & (n-1)) == 0