Adv2018/D13.2/Program.cs

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

namespace D13._2
{
    class Track : Dictionary<(int x, int y), char> { };
    class Carts : List<(int x, int y, int vx, int vy, int t)> { };

    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) return;
            if (File.Exists(args[0]) == false) return;
            var file = File.OpenText(args[0]);

            var track = new Track();
            var carts = new Carts();

            FillTrack(file, track, carts);

            int? last = null;
            do
            {
                carts.Sort((a, b) => a.x.CompareTo(b.x));
                carts.Sort((a, b) => a.y.CompareTo(b.y));

                last = lastCart(carts);

                if (last == null) tick(track, carts);

            } while (last == null);

            tick(track, carts);

            var l = carts[last.Value];
            Console.WriteLine($"The answer is \"{l.x},{l.y}\" ({l.vx},{l.vy})");
        }

        private static void FillTrack(StreamReader file, Track track, Carts carts)
        {
            int y = 0;
            do
            {
                var line = file.ReadLine();
                if (line == null) break;

                for (int x = 0; x < line.Length; ++x)
                {
                    char c = line[x];
                    if (c == ' ') continue;

                    if (isCart(c))
                    {
                        carts.Add(getCart(c, x, y));
                        c = c == '>' || c == '<' ? '-' : '|';
                    }

                    track[(x, y)] = c;
                }

                y++;

            } while (true);
        }

        private static void tick(Track track, Carts carts)
        {
            for (var i = 0; i < carts.Count; ++i)
            {
                var cart = carts[i];
                if (cart == default) continue;

                cart.x += cart.vx;
                cart.y += cart.vy;

                if (inter(carts, cart, i)) continue;

                var c = track[(cart.x, cart.y)];

                var ncart = getCart(c, cart);
                carts[i] = ncart;
            }
        }

        static int? lastCart(Carts carts)
        {
            int count = 0;
            int? cart = null;

            for (var i = 0; i < carts.Count; ++i)
            {
                if (carts[i] == default) continue;

                cart = i;
                count++;
            }
            return count == 1 ? cart : null;
        }

        static bool inter(Carts carts, (int x, int y, int vx, int vy, int t) cj, int skip)
        {
            for (var i = 0; i < carts.Count; ++i)
            {
                if (i == skip) continue;

                var ci = carts[i];
                if (ci == default) continue;

                if (ci.x == cj.x && ci.y == cj.y)
                {
                    carts[i] = default;
                    carts[skip] = default;
                    return true;
                }
            }

            return false;
        }

        static bool isCart(char c)
        {
            return c == '>' || c == '<' || c == '^' || c == 'v';
        }

        static (int x, int y, int vx, int vy, int t) getCart(char c, int x, int y)
        {
            switch (c)
            {
                case '>': return (x, y, +1, +0, 0);
                case '<': return (x, y, -1, +0, 0);
                case '^': return (x, y, +0, -1, 0);
                case 'v': return (x, y, +0, +1, 0);
            }
            return default;
        }

        static (int x, int y, int vx, int vy, int t) getCart(char c, (int x, int y, int vx, int vy, int t) cart)
        {
            if (c == '|' || c == '-') return cart;
            if (c == '+' && cart.t == 1)
            {
                cart.t++;
                return cart;
            }

            switch (cart)
            {
                case var t when t.vx == 1 && t.vy == 0:

                    if (c == '/') return (cart.x, cart.y, +0, -1, cart.t);
                    if (c == '\\') return (cart.x, cart.y, +0, +1, cart.t);
                    if (c == '+' && cart.t == 0) return (cart.x, cart.y, +0, -1, 1);
                    if (c == '+' && cart.t == 2) return (cart.x, cart.y, +0, +1, 0);
                    return default;

                case var t when t.vx == -1 && t.vy == 0:

                    if (c == '/') return (cart.x, cart.y, +0, +1, cart.t);
                    if (c == '\\') return (cart.x, cart.y, +0, -1, cart.t);
                    if (c == '+' && cart.t == 0) return (cart.x, cart.y, +0, +1, 1);
                    if (c == '+' && cart.t == 2) return (cart.x, cart.y, +0, -1, 0);
                    return default;

                case var t when t.vx == 0 && t.vy == 1:

                    if (c == '/') return (cart.x, cart.y, -1, +0, cart.t);
                    if (c == '\\') return (cart.x, cart.y, +1, +0, cart.t);
                    if (c == '+' && cart.t == 0) return (cart.x, cart.y, +1, +0, 1);
                    if (c == '+' && cart.t == 2) return (cart.x, cart.y, -1, +0, 0);
                    return default;

                case var t when t.vx == 0 && t.vy == -1:

                    if (c == '/') return (cart.x, cart.y, +1, +0, cart.t);
                    if (c == '\\') return (cart.x, cart.y, -1, +0, cart.t);
                    if (c == '+' && cart.t == 0) return (cart.x, cart.y, -1, +0, 1);
                    if (c == '+' && cart.t == 2) return (cart.x, cart.y, +1, +0, 0);
                    return default;
            }
            return default;
        }
    }
}