MoreRegex/6.EmailStatistics_dictionary

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

public class Example

{
    public static void Main(string[] args)

    {
        int n = int.Parse(Console.ReadLine());

        Dictionary<string, List<string>> valid = new Dictionary<string, List<string>>();

        Regex r = new Regex(@"^[A-Za-z]{5,}@[a-z]{3,}(\.com|\.bg|\.org)$");

        for (int i = 0; i < n; i++)
        {

            string input = Console.ReadLine();
            if (!r.Match(input).Success)
            {
                continue;
            }
            string[] splt = input.Split('@').ToArray();
            if (valid.ContainsKey(splt[1]))
            {
                if (valid[splt[1]].Any(t => t == splt[0]))
                {
                    continue;
                }
                valid[splt[1]].Add(splt[0]);
            }
            else
            {
                valid.Add(splt[1], new List<string>() { splt[0] });
            }
        }

        foreach (var domain in valid.OrderByDescending(t => t.Value.Count))
        {
            Console.WriteLine($"{domain.Key}:");
            foreach (var user in domain.Value)
            {
                Console.WriteLine($"### {user}");
            }
        }

    }
}