0191: Number of 1 Bits

Problem Statement

Given a positive integer n, write a function that returns the number of set bits in its binary representation (also known as the Hamming weight).

Example 1:

Input: n = 11

Output: 3

Explanation:

The input binary string 1011 has a total of three set bits.

Example 2:

Input: n = 128

Output: 1

Explanation:

The input binary string 10000000 has a total of one set bit.

Example 3:

Input: n = 2147483645

Output: 30

Explanation:

The input binary string 1111111111111111111111111111101 has a total of thirty set bits.

Constraints:

  • 1 <= n <= 231 - 1

Follow up: If this function is called many times, how would you optimize it?

Code Solution

class Solution:
    def hammingWeight(self, n):
        count = 0
        while n:
            count += n % 2
            n //= 2
        return count