Maximum Difference by Remapping a Digit

My solution just involved transforming num into a string twice:

• once for the maxNum
• once for the minNum

and then I just determine what number I should be swapping while iterating through the digits before swapping out the respective digits with 9 (for maxNum) and 0 (for minNum).

Finally, I can just return the difference between maxNum and minNum.

code

class Solution {
public:
    int minMaxDifference(int num) {
        string maxNum = to_string(num);
        string minNum = to_string(num);
        char numToChangeForMax = 'a';
        char numToChangeForMin = minNum[0];
        int i = 0;
        for (; i < maxNum.size() && numToChangeForMax == 'a'; ++i) {
            if (maxNum[i] != '9') {
                numToChangeForMax = maxNum[i];
                maxNum[i] = '9';
            }
            if (minNum[i] == numToChangeForMin) {
                minNum[i] = '0';
            }
        }
        for (; i < maxNum.size(); ++i) {
            if (maxNum[i] == numToChangeForMax) {
                maxNum[i] = '9';
            }
            if (minNum[i] == numToChangeForMin) {
                minNum[i] = '0';
            }
        }
        return stoi(maxNum) - stoi(minNum);
    }
};

complexity

• Time: O(log(n)) where n is num
• Space: O(log(n))

learnings

• you can do it with O(1) space complexity by using math

time taken

• 8 minutes and 32 seconds (oops)