number-of-1-bits.py

from __future__ import print_function
# Time:  O(logn) = O(32)
# Space: O(1)
#
# Write a function that takes an unsigned integer
# and returns the number of '1' bits it has (also known as the Hamming weight).
#
# For example, the 32-bit integer '11' has binary representation 00000000000000000000000000001011,
# so the function should return 3.
#
class Solution:
    # @param n, an integer
    # @return an integer
    def hammingWeight(self, n):
        result = 0
        while n:
            n &= n - 1
            result += 1
        return result

if __name__ == '__main__':
  print(Solution().hammingWeight(11))