func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<int> v[27];   bool vis[27];   vector<pair<int, int> > pr;   int cnt, flag;   void dfs(int nod, int dest) {     int i;     vis[nod] = 1;     if (nod == dest) {       flag = 1;       return;     }     for (i = 0; i < v[nod].size(); i++) {       int curr = v[nod][i];       if (vis[curr] == 0) {         dfs(curr, dest);       }     }     return;   }   int main() {     ios::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     int n, i;     cin >> n;     string s1, s2;     cin >> s1 >> s2;     for (i = 0; i < n; i++) {       flag = 0;       memset(vis, 0, sizeof(vis));       int nod = s1[i] -  a  + 1;       int dest = s2[i] -  a  + 1;       dfs(nod, dest);       if (flag == 0) {         cnt++;         pr.push_back(make_pair(nod, dest));         v[nod].push_back(dest);         v[dest].push_back(nod);       }     }     cout << cnt << endl;     for (i = 0; i < pr.size(); i++) {       char ch1 = pr[i].first +  a  - 1, ch2 = pr[i].second +  a  - 1;       cout << ch1 <<     << ch2 << endl;     }     return 0;   }   