191. Number of 1 Bits

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.

题目含义：计算出给定数字中比特位为1的数量

    // you need to treat n as an unsigned value
    public int hammingWeight(int n) {
//        return Integer.bitCount(n);

//        方法二
        int count = 0;
//        while (n != 0) {
//            count += (n & 1);
//            n = n >>> 1;
//        }

//        方法三
        while (n != 0) {
            count++;
            n &= (n - 1);
        }

        return count;
    }