476. Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:

1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. 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.
含义：给定一个正整数，对该数的二进制表示形式，从最高位的1开始向后按位取反

    public int findComplement(int num) {
//        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，然后概述和mask进行异或即可。
//        例如：82的二进制是01010010，我们的构造的掩码为mask=01111111，两者异或则为00101101，即是所要的结果。
        int mask = 1;int temp=num;
        while (temp>0)
        {
            temp>>=1;
            mask<<=1;
        }
        return num^(mask-1);//把最初的一位1去掉     
    }