Number of 1 Bits

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).

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 <= 2^31 - 1

Follow up:

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

Solution

• binary로 값 만들기

Code

C++

class Solution {
    int hammingWeight(int n)
    {
        int cnt = 0;
        while (n >= 1)
        {
            cnt = (n % 2 == 1) ? cnt+1 : cnt;
            n /= 2;
        }
        return cnt;
    }
};