191. Number of 1 Bits

Problem

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?

Solution

class Solution {
public:
    int hammingWeight(int n) {
        int count = 0;
        while (n > 0) {
            if (n & 1) count++;
            n >>= 1;
        }
        return count;
    }
};