Adv2016/D02.1/Program.cs

using System;
using System.IO;

namespace D02._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 inputs = new string[3,3] { { "1", "2", "3" }, { "4", "5", "6" }, { "7", "8", "9" } };
            (int x, int y) finger = (1, 1);

            string answer = "";

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

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

                        if (finger.x < 0) finger.x = 0;
                        if (finger.x > 2) finger.x = 2;
                        if (finger.y < 0) finger.y = 0;
                        if (finger.y > 2) finger.y = 2;
                    }

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

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