RoliTheCoder80/100

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

class RoliTheCoder
{
    static void Main()
    {
        var idsAndEvents = new Dictionary<string, string>();

        var eventsAndParticipants = new SortedDictionary<string,
            SortedSet<string>>();

        string input = Console.ReadLine();
        while (input != "Time for Code")
        {
            if (!Regex.IsMatch(input, @"(?<id>\d+)\s+#(?<event>\w+)(?<prtcpnts>((?:\s+@\w+)+)?)"))
            {
                input = Console.ReadLine();
                continue;
            }

            var inputArgs = input.Split(new char[] {' ', '\t', '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries).ToArray();

            if (!Regex.IsMatch(inputArgs[1], @"#\w+"))
            {
                input = Console.ReadLine();
                continue;
            }

            string id = inputArgs[0];
            string eventName = inputArgs[1].Remove(0, 1).ToString();

            if (idsAndEvents.ContainsKey(id) && !idsAndEvents.ContainsValue(eventName))
            {
                input = Console.ReadLine();
                continue;
            }

            SortedSet<string> participants = new SortedSet<string>();

            if (inputArgs.Length > 2)
            {
                for (int i = 2; i < inputArgs.Length; i++)
                {
                    participants.Add(inputArgs[i].ToString());
                }
            }

            if (!eventsAndParticipants.ContainsKey(eventName))
            {
                idsAndEvents.Add(id, eventName);
                eventsAndParticipants.Add(eventName, new SortedSet<string>());
                eventsAndParticipants[eventName].UnionWith(participants);
            }
            else
            {
                eventsAndParticipants[eventName].UnionWith(participants);
            }

            input = Console.ReadLine();
        }

        var sortedEvents = new Dictionary<string, int>();
        foreach (var ev in eventsAndParticipants)
        {
            sortedEvents.Add(ev.Key, ev.Value.Count);
        }

        foreach (var evnt in sortedEvents.OrderByDescending(x => x.Value))
        {
            Console.WriteLine($"{evnt.Key} - {evnt.Value}");

            var participants = eventsAndParticipants
                .Where(x => x.Key == evnt.Key)
                .ToDictionary(x => x.Key, y => y.Value);

            foreach (var participant in participants.Values)
            {
                foreach (var p in participant)
                {
                    Console.WriteLine($"{p}");

                }
            }
        }
    }
}