func_code_string: #include <bits/stdc++.h>   const double eps = 1e-7, PI = 3.1415926;   const int N = 2e5 + 10;   using namespace std;   int n, q, m, k, x, y, a[N], mx = -1, mn = 1e9, sum, t;   char c[N];   string s, s1, s2;   map<pair<int, char>, int> mp;   vector<int> vec;   int main() {     cin >> q;     while (q--) {       cin >> n;       cin >> s1 >> s2;       y = 0;       mp.clear();       sum = 0;       for (int i = 0; i < 20; i++) {         char v =  a  + i;         mn = 1e9;         int hg = 20;         while (hg--) {           mn = 1e9;           for (int j = 0; j < n; j++) {             if (s1[j] == v && s2[j] != s1[j]) {               mn = min(mn, s2[j] - s1[j]);             }           }           for (int j = 0; j < n; j++) {             if (s1[j] == v && s2[j] != s1[j]) {               s1[j] += mn;             }           }           if (mn < 0) y = 1;           if (mn == 1e9)             break;           else             sum++;         }       }       if (!y)         cout << sum << endl;       else         cout << -1 << endl;     }     return 0;   }   