3.Post Office

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

namespace _3._Post_Office
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] symbols = Console.ReadLine().Split('|').ToArray();

            string firstPattern = @"([#$%*&])[A-Z]+\1";
            string secondPattern = @"[0-9]{2}:[0-9]{2}";
            string letterPattern = @"[A-Z]";

            Match matchLetters = Regex.Match(symbols[0], firstPattern);
            MatchCollection matchesLetter = Regex.Matches(matchLetters.ToString(), letterPattern);

            MatchCollection matchesNumbers = Regex.Matches(symbols[1], secondPattern);

            var number = new Dictionary<int, int>();
            var letters = new Dictionary<string, int>();

            foreach (Match item in matchesNumbers)
            {
                int[] arr = item.ToString().Split(':').Select(x => x.TrimStart('0')).Select(int.Parse).ToArray();

                if(number.ContainsKey(arr[0]))
                {
                    continue;
                }
                number.Add(arr[0], arr[1]);
            }

            foreach (Match item in matchesLetter)
            {
                foreach (var items in number)
                {
                    if((int)Convert.ToChar(item.ToString()) == items.Key)
                    {
                        if(letters.ContainsKey(item.ToString()))
                        {
                            continue;
                        }
                        letters.Add(item.ToString(), items.Value+1);
                    }
                }

            }
            string[] words = symbols[2].Split(' ').ToArray();

            foreach (var item in letters)
            {
                foreach (var items in words)
                {
                    if(items[0] == Convert.ToChar(item.Key) && items.Length == item.Value)
                    {
                        Console.WriteLine(items);
                    }
                }
            }
        }
    }
}