Problem

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

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.

Solution1 (My Solution)

class Solution {
public:
    int findComplement(int num) {
        std::bitset<32> bits(num);
        int endPos = ignoreLeadingZero(bits);
        for (int i = 0; i <= endPos; i++){
             bits[i] = !bits[i];    
        }
        
        return int(bits.to_ulong());
    }
    
private:
    int ignoreLeadingZero(bitset<32>& bits){
        size_t bitsLength = bits.size();
        for (int i = bitsLength - 1; i >= 0; i--){
            if (bits[i] == 0) continue;
            else return i;
        }
    }
};

Solution2

class Solution {
public:
    int findComplement(int num) {
        unsigned mask = ~0;
        while (num & mask) mask <<= 1;
        return ~mask & ~num;
    }
};

• Solution2 通过求其掩码的方式，基于二进制运算，速度较快。