Number of 1 Bits

Write a function that takes the binary representation of a positive integer and returns the number of set bits it has (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.

Constraints:

• 1 <= n <= 2^31 - 1