03. Cities by Continent and Country

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _03.Cities_by_Continent_and_Country
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());

            var continents = new Dictionary<string, Dictionary<string, List<string>>>();

            for (int i = 0; i < n; i++)
            {
                var tokens = Console.ReadLine().Split();
                var continent = tokens[0];
                var country = tokens[1];
                var city = tokens[2];

                if (!continents.ContainsKey(continent))
                {
                    continents[continent] = new Dictionary<string,List<string>>();
                }
                if (!continents[continent].ContainsKey(country))
                {
                    continents[continent][country] = new List<string>();
                }
                continents[continent][country].Add(city);
            }

            foreach (var continentCountry in continents)
            {
                var continentName = continentCountry.Key;
                var countries = continentCountry.Value;
                Console.WriteLine("{0}:", continentName);

                foreach (var countryCity in countries)
                {
                    var countryName = countryCity.Key;
                    var cities = countryCity.Value;

                    Console.WriteLine("  " + countryName + " -> "  + string.Join(", ", cities));
                }
            }
        }
    }
}