1737. Change Minimum Characters to Satisfy One of Three Conditions

You are given two strings a and b that consist of lowercase letters. In one operation, you can change any character in a or b to any lowercase letter.

Your goal is to satisfy one of the following three conditions:

• Every letter in a is strictly less than every letter in b in the alphabet.
• Every letter in b is strictly less than every letter in a in the alphabet.
• Both a and b consist of only one distinct letter.

Return the minimum number of operations needed to achieve your goal.

class Solution {
public:
    int minCharacters(string a, string b) {
        int res(INT_MAX), aC(0), bC(0), aL(a.length()), bL(b.length());
        unordered_map<char, int> ma, mb;
        for(auto& ca : a) ma[ca] += 1;
        for(auto& cb : b) mb[cb] += 1;
        
        for(auto c = 'a'; c <= 'z'; c++) {
            res = min(res, aL - ma[c] + bL - mb[c]);
        }
        
        for(auto c = 'z'; c > 'a'; c--) {
            res = min(res, aL - ma[c] + mb[c]);
            res = min(res, bL - mb[c] + ma[c]);
            ma[c - 1] += ma[c];
            mb[c - 1] += mb[c];
        }
        
        return res;
    }
};