Number of 1 bits

Time: O(LogN)=O(32); Space: O(1); easy

Write a function that takes an unsigned integer and returns the number of ‘1’ bits it has (also known as the Hamming weight).

Example 1:

Input: num = 11

Output: 3

Explanation:

• Binary representation (as 32-bit integer): 00000000000000000000000000001011

class Solution(object):
    def hammingWeight(self, num) -> int:
        """
        :type num: int
        :rtype: int
        """
        result = 0
        while num:
            num &= num - 1
            result += 1
        return result

s = Solution1()
num = 11
assert s.hammingWeight(num) == 3

See also:

https://leetcode.com/problems/number-of-1-bits

https://www.lintcode.com/problem/number-of-1-bits