func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, k;   string s1, s2;   vector<pair<string, string> > ans;   map<string, int> u;   int main() {     cin >> n;     for (int i = 1; i <= n; i++) {       cin >> s1 >> s2;       map<string, int>::iterator it = u.find(s1);       if (it == u.end()) {         u[s1] = k, u[s2] = k;         ans.push_back(make_pair(s1, s2));         k++;       } else {         u[s2] = it->second;         ans[it->second].second = s2;       }     }     cout << ans.size() << endl;     for (size_t i = 0; i < ans.size(); i++) {       cout << ans[i].first <<     << ans[i].second << endl;     }     return 0;   }   