func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     cin.tie(0);     cin.sync_with_stdio(0);     cout.tie(0);     string s, t, b;     int n;     vector<pair<char, char>> v;     set<char> z;     bool fine = false;     char a[26];     for (int i = 0; i < 26; i++) a[i] =  @ ;     cin >> s >> t;     for (int i = 0; i < s.length(); i++)       if (a[s[i] -  a ] ==  @ )         a[s[i] -  a ] = t[i];       else if (a[s[i] -  a ] != t[i]) {         cout << -1;         return 0;       }     for (int i = 0; i < 26; i++)       if (a[i] !=  @ ) {         if (((char)(i +  a ) != a[a[i] -  a ]) && ( @  != a[a[i] -  a ])) {           cout << -1;           return 0;         }       }     for (int i = 0; i < 26; i++)       if ((a[i] != (char)( a  + i)) && (a[i] !=  @ )) {         fine = false;         for (int j = 0; j < v.size(); j++)           if ((v[j].first == a[i]) && (v[j].second == (char)( a  + i)))             fine = true;         if (fine == false) v.push_back(make_pair((char)( a  + i), a[i]));       }     for (int i = 0; i < v.size(); i++) z.insert(v[i].second);     if (z.size() != v.size()) {       cout << -1;       return 0;     }     cout << v.size() << endl;     for (int i = 0; i < v.size(); i++)       cout << v[i].first <<     << v[i].second << endl;     return 0;   }   