题目：

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.
Note: The given integer is guaranteed to fit within the range of a
32-bit signed integer. You could assume no leading zero bit in the
integer’s binary representation.
Example 1:
Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.
Example 2:
Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

解释：
二进制取反。
python投机取巧:
先用bin变成二进制，然后用1减去每一位进行翻转
c++:
如果我们能知道该数最高位的1所在的位置，就可以构造一个长度和该数据所占位置一样长的一个掩码mask，然后该数字和mask进行异或即可。
例如：5的二进制是101，我们的构造的掩码为mask=111，两者异或则为010，即是所要的结果。
取反就是和与它长度相同的全1二进制进行异或

python代码：

class Solution(object):
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        num_bin=bin(num)[2:]
        result=''
        for n in num_bin:
            r=str(1-int(n))
            result+=r
        return int(result,2)

c++代码：

class Solution {
public:
    int findComplement(int num) {
        int mask=1;
        int n=num;
        while(n>0)
        {
            mask=mask<<1;
            n=n>>1;
        }
        return (mask-1)^num;
    }
};

python写法：

class Solution(object):
    def findComplement(self, num):
        """
        :type num: int
        :rtype: int
        """
        n=num
        mask=1
        while(n>0):
            mask=mask<<1
            n=n>>1
        return (mask-1)^num

这种异或的写法速度显然更快。

总结：
取反就是和与它长度相同的全1二进制进行异或