Number of 1 Bits
Updated Jan 31, 2026
Problem
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).
Constraints
1 <= n <= 2^31 - 1
Follow Up
If this function is called many times, how would you optimize it?
Examples
Example 1
Input:
n = 11 (binary: 1011)
Output:
3
The input binary string 1011 has a total of three set bits.
Example 2
Input:
n = 128 (binary: 10000000)
Output:
1
Example 3
Input:
n = 2147483645
Output:
30
Function Signature
def hammingWeight(self, n: int) -> int
How to Submit
Implement a Solution class with a hammingWeight method.
Your method will be called with the input parameters and should return the answer.