BKmWF8 - Online C++0x Compiler & Debugging Tool

#include <iostream>
#include <vector>
#include<unordered_map>
#include <string>
using namespace std;
#include<algorithm>
#include<set>

#define Fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ll long long


vector<pair<string, string>>ans;

unordered_map<string, string>mp;
set<string>st;
string find1(string second) {
    string name = second;

    auto it = mp.find(second);
    if (it != mp.end()) {

        name = find1(it->second);

    }
    return name;
}
void sol() {

    int n; cin >> n;

    while (n--) {
        string old, newname; cin >> old >> newname; mp.insert({ old,newname });
    }
    for (auto it : mp) {
        if (st.find(it.first) == st.end()) {
            ans.push_back({ it.first, find1(it.second) });

        }
    }
    cout << ans.size() << endl;
    reverse(ans.begin(), ans.end());
    for (auto it : ans) {
        cout << it.first << " " << it.second << endl;
    }

}

int main() {
    Fast
        int t = 1;
    while (t--) {
        sol();
    }
    return 0;
}