Number of 1 Bits
描述
Write a function that takes an unsigned integer and returns the number of ’1' bits it has (also known as the Hamming weight).
For example, the 32-bit integer 11 has binary representation 00000000000000000000000000001011, so the function should return 3.
分析
最直接的方法，做32次右移，统计出1的个数。
第二个方法，来自 "Hacker's Delight" 这本书。