03. Cities by Continent and Country

#include <iostream>
#include <string>
#include <map>
#include <set>

using namespace std;

int main() {
    int n;
    cin >> n;

    map<string, map<string, set<string>>> info;

    string continent, country, city;

    for (size_t i = 0; i < n; i++) {
        cin >> continent >> country >> city;
        info[continent][country].insert(city);
    }

    for (auto i = info.begin(); i != info.end(); i++) {
        cout << '\n' << i->first << ':';

        for (auto j = i->second.begin(); j != i->second.end(); j++) {
            cout << '\n' << j->first << " -> ";
            int len = j->second.size();
            for (auto k = j->second.begin(); k != j->second.end(); k++) {
                cout << k->c_str();
                if (--len != 0) {
                    cout << ", ";
                }
            }
        }
    }

    return 0;
}