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.

思路：

统计num对应的二进制所占的位数n，然后用2ⁿ-1 -num即可。  

int findComplement(int num)
{
   int NUM = num;
    int tmp =1;
    while(num)
    {
        num>>=1;
        tmp <<=1;
    }
    return  tmp - NUM -1;
}

[leetcode-476-Number Complement]