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?

submission

// trick: n &= (n - 1); removes a set bit of n
// however in Rust we have count_ones 
// which should be more efficient
impl Solution {
    pub fn hamming_weight(mut n: i32) -> i32 {
        n.count_ones() as _
    }
}