Problem - Number of 1 Bits

Given an unsigned integer $n$, return the number of 1 bits in its binary representation (also called Hamming weight).

For example, if $n = 11$ (which is $1011_2$), the answer is 3 because there are three 1s. If $n = 128$ (which is $10000000_2$), the answer is 1.

This is your first bit manipulation problem. Think about how you can check each bit of $n$ and count the 1s. Before reading on, try to sketch an algorithm yourself.