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191. 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.

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 result = 0;
        while (n != 0){
            if (n % 2 != 0){
                result++;
            }
            n = n >> 1;
        }
        return result;
    }
}
// TC: O(n)
// SC: O(1)