Question

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

Solution

There are 4 ways of doing this:

1. keep dividing the number with 2 until it becomes 1;
2. convert the number to base-2 integer and check only the first digit is 1;
3. if the range if input is bounded, we can find the largest power of two in the range (say, max_power_2), and max_power_2 % n == 0 is true.

class Solution(object):
    def isPowerOfTwo(self, n):
        """
        :type n: int
        :rtype: bool
        """
        if n <= 0:
            return False
        elif n == 1:
            return True
        else:
            while n != 1:
                if n % 2 == 0:
                    n //= 2
                else:
                    return False
            return True