# Built in solution with built-in function:

class Solution:

def hammingWeight(self, n):

"""

:type n: int

:rtype: int

"""

return bin(n).count('1')

'''

Using bit operation to cancel a 1 in each round

Think of a number in binary n = XXXXXX1000, n - 1 is XXXXXX0111.

n & (n - 1) will be XXXXXX0000 which is just remove the last significant 1

'''

class Solution:

def hammingWeight(self, n):

"""

:type n: int

:rtype: int

"""

c = 0

while n:

n &= n - 1

c += 1

return c

# Recursively

class Solution:

def hammingWeight(self, n, count=0):

return self.hammingWeight(n & n-1, count+1) if n!=0 else count

'''

Explanation:

Use bitwise operations:

&1 returns 1 if the last bit of the result of n>>i == 1, else 0

By using n>>i, we shift the bits to the right by i places

this way, every bit of n is the 'last bit' of n>>i at one point

sum up the number of 1s that we found that way

'''

def hammingWeight(self, n: int) -> int:

return sum((n>>i&1 for i in range(32)))