Flip Bits

题目：

Determine the number of bits required to flip if you want to convert integer n to integer m.

Given n = 31 (11111), m = 14 (01110), return 2.

分析：

题目很简单，但是反应的思维方法很经典

1. 如何统计how many bits are set
2. 如何处理负数

解法：

class Solution {
public:
    /**
     *@param a, b: Two integer
     *return: An integer
     */
    int bitSwapRequired(int a, int b) {
        // write your code here
        unsigned temp = a ^ b;
        int res = 0;
        while (temp) {
            res += temp & 1;
            temp = temp >> 1;
        }
        return res;
    }
};