Number of 1 Bits

Problem

Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).

For example, the 32-bit integer ’11' has binary representation 00000000000000000000000000001011, so the function should return 3.

Solution

O(1) time and O (1) space (Int is fixed 32-bit)

public class Solution {
    public int hammingWeight(int n) {
        int res = 0;
        while (n != 0) {
            res += (n & 1);
            n = n >>> 1;
        }
        return res;
    }
}

Analysis

This problem is actually asking the implementation of Integer.bitCount()
Which we solved in the problem Hamming Distance
The only difference is that we use >>> in this problem rather than >>
Because the given integer is unsigned so we need to use unsigned shift >>>
This avoid the infinite calculation