05. Courses

using System;
using System.Collections.Generic;
using System.Linq;

namespace Courses
{
    class Program
    {
        public static void Main()
        {
            Dictionary<string, List<string>> courses = new Dictionary<string, List<string>>();

            string command;

            while ((command = Console.ReadLine()) != "end")
            {
                string[] current = command.Split(" : ");

                string course = current[0];
                string student = current[1];

                if (!courses.ContainsKey(course))
                {
                    courses.Add(course, new List<string>());
                }

                courses[course].Add(student);
            }

            foreach (var course in courses)
            {
                Console.WriteLine($"{course.Key}: {course.Value.Count()}");
                Console.WriteLine($"-- {string.Join("\n-- ", course.Value)}");
            }
        }
    }
}