Adv2016/D07.1/Program.cs

using System;
using System.IO;
using System.Text.RegularExpressions;

namespace D07._1
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) throw new ArgumentException();
            if (File.Exists(args[0]) == false) throw new FileNotFoundException();

            var r = new Regex(@"(?!^.*\[\w*(\w)(?!\1)(\w)\2\1\w*\])^.*(\w)(?!\3)(\w)\4\3", RegexOptions.Multiline)
                .Matches(File.ReadAllText(args[0]));
            Console.WriteLine($"The answer is : {r.Count}");
        }
    }
}