Number of 1 Bits

## Problem Given a positive integer `n`, write a function that returns the number of **set bits** (bits equal to `1`) in its binary representation. This is also known as the **Hamming weight**. ## Examples **Example 1:** ``` Input: n = 11 Output: 3 Explanation: 11 in binary is 1011, which has three 1-bits. ``` **Example 2:** ``` Input: n = 128 Output: 1 Explanation: 128 in binary is 10000000, which has one 1-bit. ``` **Example 3:** ``` Input: n = 255 Output: 8 Explanation: 255 in binary is 11111111, which has eight 1-bits. ``` ## Hints - Use `n & 1` to check the least significant bit, then right-shift `n`. - Alternatively, use the bit trick `n = n & (n - 1)` which clears the lowest set bit each iteration — count how many times you apply it before `n` becomes 0. - In Python, `bin(n).count('1')` works but try the bit manipulation approach.