func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     string s, t;     cin >> s >> t;     map<char, char> m;     bool ans = true;     vector<pair<char, char>> v;     int count = 0;     for (int i = 0; i < s.size(); i++) {       if (m.find(s[i]) != m.end()) {         if (m[s[i]] != t[i]) {           ans = false;           break;         } else {           continue;         }       } else {         if (m.find(t[i]) != m.end()) {           ans = false;           break;         } else {           m[s[i]] = t[i];           m[t[i]] = s[i];           if (s[i] != t[i]) {             v.push_back({s[i], t[i]});             count++;           }         }       }     }     if (ans) {       cout << count << endl;       for (int i = 0; i < count; i++)         cout << v[i].first <<     << v[i].second << endl;     } else       cout <<  -1 ;     return 0;   }   