Adv2016/D02.2/Program.cs

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

namespace D02._2
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) throw new ArgumentException();
            if (File.Exists(args[0]) == false) throw new FileNotFoundException();

            string NUL = null;
            var inputs = new string[5,5] { 

                { NUL, NUL, "1", NUL, NUL }, 
                { NUL, "2", "3", "4", NUL }, 
                { "5", "6", "7", "8", "9" },
                { NUL, "A", "B", "C", NUL },
                { NUL, NUL, "D", NUL, NUL }, 

            };
            (int x, int y) finger = (0, 2);

            string answer = "";

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

                    foreach (char c in line)
                    {
                        (int x, int y) = finger;
                        switch (c)
                        {
                            case 'U': y--; break;
                            case 'D': y++; break;
                            case 'L': x--; break;
                            case 'R': x++; break;
                        }


                        if (y < 0) y = 0;
                        if (y > 4) y = 4;
                        if (x < 0) x = 0;
                        if (x > 4) x = 4;

                        if (inputs[y, x] == NUL) (x, y) = finger;
                        finger = (x, y);
                    }

                    answer += inputs[finger.y, finger.x];
                }
            }

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