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.
Credits: Special thanks to @ts for adding this problem and creating all test cases.
一个数x与x-1的与运算，就是把最低位的1置0。即 x & (x - 1)会把最低位的1置0。
int hammingWeight(uint32_t n)
{
int sum = 0;
while (n) {
++sum;
n &= (n - 1);
}
return sum;
}