Adv2015/D05.2/Program.cs

using System;
using System.Collections.Generic;
using System.IO;

namespace D05._2
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) throw new ArgumentException();
            if (File.Exists(args[0]) == false) throw new FileNotFoundException();

            int goodStrings = 0;
            using (var file = File.OpenText(args[0]))
            {
                while (true)
                {
                    var line = file.ReadLine();
                    if (line == null) break;

                    if (IsGoodString(line)) goodStrings++;
                }
            }

            Console.WriteLine($"The answer is : {goodStrings}");
        }

        private static bool IsGoodString(string line)
        {
            HashSet<(char a, char b)> repeted = new HashSet<(char a, char b)>();
            bool repetitionExists = false;
            bool betweenExists = false;

            int same = 1;
            char last = '\0', lalast = '\0';
            foreach (var c in line)
            {
                if (c == last) same++;
                else same = 1;

                if (same == 4) repetitionExists = true;

                if (repetitionExists == false && same != 3)
                {
                    bool exists = repeted.Add((last, c));
                    repetitionExists = exists == false;
                }

                if (lalast == c) betweenExists = true;

                if (betweenExists && repetitionExists) break;

                lalast = last;
                last = c;
            }

            return repetitionExists && betweenExists;
        }
    }
}