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

# Example 1:
# Input: 00000000000000000000000000001011
# Output: 3
# Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.

# Example 2:
# Input: 00000000000000000000000010000000
# Output: 1
# Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.

# Example 3:
# Input: 11111111111111111111111111111101
# Output: 31
# Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.
 
# Note:
# Note that in some languages such as Java, there is no unsigned integer type. 
# In this case, the input will be given as signed integer type and should not affect your implementation, 
# as the internal binary representation of the integer is the same whether it is signed or unsigned.
# In Java, the compiler represents the signed integers using 2's complement notation. 
# Therefore, in Example 3 above the input represents the signed integer -3.
 
# Follow up:
# If this function is called many times, how would you optimize it?

class Solution(object):
    def hammingWeight(self, n):
        """
        :type n: int
        :rtype: int
        """
        # M1. Loop and Flip
        # res = 0
        # while n:
        #     res += n & 1
        #     n >>= 1
        # return res

        # M2. Bit Manipulation Trick
        cnt = 0
        while n:
            n = n & (n-1)
            cnt += 1
        return cnt
    