Adv2016/D07.2/Program.cs

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

namespace D07._2
{
    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)(?!\1)(\w)\1(?:(?!\w*\]).*\2\1\2(?=\w*\])|(?=\w*\]).*\2\1\2(?!\w*\]))", RegexOptions.Multiline)
                .Matches(File.ReadAllText(args[0]));
            Console.WriteLine($"The answer is : {r.Count}");
        }
    }
}