func_code_string: #include <bits/stdc++.h>   using namespace std;   char arr[300];   int main() {     ios::sync_with_stdio(false);     string s, t;     cin >> s >> t;     int n = s.size();     memset(arr,  A , sizeof(arr));     if (n != t.size()) {       cout << -1;       return 0;     }     for (int i = 0; i < n; i++) {       if (arr[t[i]] !=  A ) {         if (arr[t[i]] != s[i]) {           cout << -1;           return 0;         }         continue;       }       if (arr[s[i]] ==  A ) {         arr[s[i]] = t[i];         arr[t[i]] = s[i];       }       if (arr[s[i]] != t[i]) {         cout << -1;         return 0;       }     }     vector<pair<char, char> > v;     for (int i = 0; i < 300; i++) {       if (arr[i] !=  A ) {         if (i == arr[i]) continue;         v.push_back(make_pair((char)i, arr[i]));         arr[arr[i]] =  A ;         arr[i] =  A ;       }     }     cout << v.size() << endl;     for (int i = 0; i < v.size(); i++)       cout << v[i].first <<     << v[i].second << endl;     return 0;   }   