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.
分析：mask – 1為和num二進制位等長的所有位數為1的數，與num取^可以得到和num相反的數字。

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