Adv2016/D09.2/Program.cs

using System;
using System.IO;

namespace D09._2
{
    class Program
    {

        static bool TryGetToken(string input, ref int index, out long length)
        {
            length = 0;
            int idx = index;

            if (IsCompressionToken(input, out int strlen, out int repetition, ref idx) == false)
                return false;

            long sublength = 0;
            for (var i = idx; i < idx + strlen; i++)
            {
                if (TryGetToken(input, ref i, out long len))
                    sublength += len;
                else sublength++;
            }

            idx += strlen;
            index = idx - 1;

            length = sublength * repetition;

            return true;
        }

        private static bool IsCompressionToken(string input, out int strlen, out int repetition, ref int idx)
        {
            strlen = 0;
            repetition = 0;

            if (input[idx++] != '(') return false;

            int nindex = idx;
            while (input[idx] >= '0' && input[idx] <= '9') idx++;

            strlen = int.Parse(input.Substring(nindex, idx - nindex));
            if (input[idx++] != 'x') return false;

            nindex = idx;
            while (input[idx] >= '0' && input[idx] <= '9') idx++;

            repetition = int.Parse(input.Substring(nindex, idx - nindex));

            if (input[idx++] != ')') return false;

            return true;
        }

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

            long totalLength = 0;

            var text = File.ReadAllText(args[0]);
            for (var i = 0; i < text.Length; ++i)
            {
                if (text[i] == ' ' || text[i] == '\n' || text[i] == '\t') continue;

                if (TryGetToken(text, ref i, out long length))
                    totalLength += length;
                else totalLength++;
            }

            Console.WriteLine(totalLength);
        }
    }
}