Roli The Coder

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace _02_04_RoliTheCoder
{
    class RoliTheCoder
    {
        static void Main(string[] args)
        {
            Regex pattern = new Regex(@"(?<id>\d+)\s+#(?<event>.+?)($|(?=\ ))");
            Regex participantsPattern = new Regex(@"@[a-zA-Z0-9'-]+");
            Dictionary<int, Event> events = new Dictionary<int, Event>();
            string input = string.Empty;

            while ((input = Console.ReadLine()) != "Time for Code")
            {
                Match match = pattern.Match(input);
                if (match.Success)
                {
                    int id = int.Parse(match.Groups["id"].Value);
                    string name = match.Groups["event"].Value;

                    if (events.ContainsKey(id) && events[id].Name != name)
                    {
                        continue;
                    }
                    else if (!events.ContainsKey(id))
                    {
                        events.Add(id, new Event(name));
                    }
                    MatchCollection matches = participantsPattern.Matches(input);
                    List<string> participants = new List<string>();
                    foreach (Match m in matches)
                    {
                        participants.Add(m.Value);
                    }
                    events[id].AddParticipants(participants);
                }
            }

            foreach (var pair in events.OrderByDescending(x => x.Value.Participants.Count).ThenBy(x => x.Value.Name))
            {
                Console.WriteLine($"{pair.Value.Name} - {pair.Value.Participants.Count}");

                foreach (string participant in pair.Value.Participants.OrderBy(x => x))
                {
                    Console.WriteLine(participant);
                }
            }
        }
    }

    class Event
    {
        public string Name { get; private set; }
        public HashSet<string> Participants;

        public Event(string name)
        {
            this.Participants = new HashSet<string>();
            this.Name = name;
        }

        public void AddParticipants(List<string> participants)
        {
            foreach (string participant in participants)
            {
                this.Participants.Add(participant);
            }
        }
    }
}