LeetCode刷题：476.Number Complement

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.

解题思路：

题例中5的二进制为101，补数为010,补数可以通过101 ^ 111获得，所以首先获取与num相同二进制位数的111，通过判断num左移1位是否为空可以获得其位数，进而获取mask。

解答：

class Solution {
public:
    int findComplement(int num) {
        int mask = 2, tmp = num;
        while(tmp >>= 1)
        {
            mask <<= 1;  
        }
        return num ^ (mask-1);
    }
};