Adv2015/D03.2/Program.cs

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

namespace D03._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 text = "";
            using (var file = File.OpenText(args[0]))
            {
                text = file.ReadToEnd();
            }

            (int x, int y)[] pos = new[] { (0, 0), (0, 0) };
            var visited = new HashSet<(int, int)>
            {
                (0, 0)
            };

            int santas = 2, santaId = 0;
            foreach (var c in text)
            {
                santaId = (santaId + 1) % santas;
                switch (c)
                {
                    case '>': pos[santaId].x++; break;
                    case '<': pos[santaId].x--; break;
                    case '^': pos[santaId].y--; break;
                    case 'v': case 'V': pos[santaId].y++; break;
                    default: continue;
                }
                visited.Add(pos[santaId]);
            }

            Console.WriteLine($"Answer is : {visited.Count}");
        }
    }
}