leetcode- Complement of Base 10 Integer

#. Problem

Link

1. Solution

Very smart. If you get negative number-1 for n, you would get all 1’s of left hands.

// e.g.)
// 5 : 00...00101
// -6 : 11...11010

Therefore, put all right sides 1s till it’s less than n, and do XOR.

XOR. If two digits are the same : 0, if it’s different : 1

class Solution {
public:
    int bitwiseComplement(int n) {
        int mask = 1;
        while(mask < n){
            mask = (mask << 1) + 1;
        }
        
        return mask^n;
    }
};

2. Epilogue

What I’ve learned from this exercise:

• adding several operation together could be a good way to start solving a problem