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?