func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     string s, t;     cin >> s >> t;     int flag = 0;     vector<char> arr(26,  . );     for (int i = 0; i < s.length(); i++) {       int a = int(s[i]);       int b = int(t[i]);       if (arr[a - 97] == t[i] || arr[a - 97] ==  . ) {         arr[a - 97] = t[i];         if (arr[b - 97] == s[i] || arr[b - 97] ==  . )           arr[b - 97] = char(a);         else {           cout << -1;           flag = -1;           break;         }       } else {         cout << -1;         flag = -1;         break;       }     }     if (flag != -1) {       for (int i = 0; i < 26; i++) {         if (arr[i] !=  . ) {           int x = (int)arr[i];           if (arr[x - 97] == char(i + 97) || arr[x - 97] ==  . ) {             arr[x - 97] =  . ;             continue;           } else {             cout << -1;             flag = -1;             break;           }         }       }     }     if (flag != -1) {       int sum = 0;       for (int i = 0; i < 26; i++) {         if (arr[i] !=  . ) sum++;       }       cout << sum << endl;       if (sum != 0) {         for (int i = 0; i < 26; i++) {           if (arr[i] !=  . ) cout << arr[i] <<     << char(i + 97) << endl;         }       }     }     return 0;   }   