text: # Time:  O(32), bit shift in python is not O(1), it's O(k), k is the number of bits shifted
  #             , see https://github.com/python/cpython/blob/2.7/Objects/longobject.c#L3652
  # Space: O(1)
  
  class Solution(object):
      # @param n, an integer
      # @return an integer
      def hammingWeight(self, n):
          n = (n & 0x55555555) + ((n >> 1) & 0x55555555)
          n = (n & 0x33333333) + ((n >> 2) & 0x33333333)
          n = (n & 0x0F0F0F0F) + ((n >> 4) & 0x0F0F0F0F)
          n = (n & 0x00FF00FF) + ((n >> 8) & 0x00FF00FF)
          n = (n & 0x0000FFFF) + ((n >> 16) & 0x0000FFFF)
          return n
  
  
  # Time:  O(logn/4) = O(32/4 + 8*4) = O(32)
  # Space: O(1) 
  # https://github.com/gcc-mirror/gcc/blob/master/libgcc/libgcc2.c#L856
  class Solution2(object):
      def __init__(self):
          self.__popcount_tab = \
          [ \
              0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5, \
              1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6, \
              1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6, \
              2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7, \
              1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6, \
              2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7, \
              2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7, \
              3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,4,5,5,6,5,6,6,7,5,6,6,7,6,7,7,8 \
          ]
  
      # @param n, an integer
      # @return an integer
      def hammingWeight(self, n):
          result = 0
          while n:
              result += self.__popcount_tab[n & 0xff]
              n >>= 8
          return result
  
      
  # Time:  O(logn) = O(32)
  # Space: O(1)
  class Solution3(object):
      # @param n, an integer
      # @return an integer
      def hammingWeight(self, n):
          result = 0
          while n:
              n &= n - 1
              result += 1
          return result
  
  