GameOfFifteen.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GameOfFifteen
{
    class Program
    {

        static void Main(string[] args)
        {
            var game = new Game();

            Scramble(game, 100);

            while (true)
            {
                Console.Clear();
                PrintGrid(game);

                Console.WriteLine();
                Console.WriteLine("Enter your move(or q to quit): ");

                var key = Console.ReadKey();

                switch (key.Key)
                {
                    case ConsoleKey.LeftArrow:
                        game.MoveBy(-1, 0);
                        break;
                    case ConsoleKey.RightArrow:
                        game.MoveBy(1, 0);
                        break;
                    case ConsoleKey.UpArrow:
                        game.MoveBy(0, -1);
                        break;
                    case ConsoleKey.DownArrow:
                        game.MoveBy(0, 1);
                        break;
                    default:
                        if (key.KeyChar == 'q')
                            return;
                        break;
                }

                if (game.Won())
                {
                    Console.Clear();
                    PrintGrid(game);

                    Console.WriteLine();
                    Console.WriteLine("You won!!");
                    Console.WriteLine();
                    Console.WriteLine("Press any key to quit.");
                
                    Console.ReadKey();
                    return;
                }
            }
        }

        private static void Scramble(Game game, int count)
        {
            var random = new Random();

            var directions = new[]
            {
                new Position{X = 0, Y = 1}, 
                new Position{X = 0, Y = -1}, 
                new Position{X = 1, Y = 0}, 
                new Position{X = -1, Y = 0}, 
            };

            while (count > 0)
            {
                count--;

                var d = directions[random.Next(4)];

                game.MoveBy(d.X, d.Y);
            }
        }


        private static void PrintGrid(Game game)
        {
            for (int x = 0; x < game.Width; x++)
            {
                for (int y = 0; y < game.Height; y++)
                {
                    var n = game[x, y].ToString();
                    if (n == "-1") n = "";
                    Console.Write("| {0} ", n.PadLeft(2));
                }
                Console.WriteLine("|");
            }
        }
    }

    class Position
    {
        public int X { get; set; }
        public int Y { get; set; }
    }

    class Game
    {
        public int[,] Grid { get; set; }

        public Position CurrentPosition { get; private set; }

        private int _numTiles;

        public Game()
        {
            this.Grid = new[,]
            {
                {1, 2, 3, 4},
                {5, 6, 7, 8},
                {9, 10, 11, 12},
                {13, 14, 15, -1}
            };

            _numTiles = Width*Height;

            UpdateCurrentPosition();
        }

        public bool MoveBy(int x, int y)
        {
            var current = this.CurrentPosition;
            var newPos = new Position {X = current.X + x, Y = current.Y + y};
            if (!CanMoveTo(newPos))
                return false;

            var source = this[current];
            var dest = this[newPos];


            this[current] = dest;
            this[newPos] = source;

            this.CurrentPosition = newPos;

            return true;
        }

        public int this[Position p]
        {
            get { return this.Grid[p.Y, p.X]; }
            set { this.Grid[p.Y, p.X] = value; }
        }

        public int this[int x, int y]
        {
            get { return this.Grid[x, y]; }
            set { this.Grid[x, y] = value; }
        }

        public bool Won()
        {
            var counter = 1;

            foreach (var n in IterateCells())
            {
                if (n == -1 && counter == _numTiles)
                    return true;

                if (n != counter)
                    return false;

                counter++;
            }

            return false;
        }

        public int Height
        {
            get { return this.Grid.GetUpperBound(1) + 1; }
        }

        public int Width
        {
            get { return this.Grid.GetUpperBound(0) + 1; }
        }

        private void UpdateCurrentPosition()
        {
            for (var x = 0; x < Width; x++)
                for (var y = 0; y < Height; y++)
                    if (this[x, y] == -1)
                        this.CurrentPosition = new Position {X = x, Y = y};
        }

        private bool CanMoveTo(Position pos)
        {
            return pos.X < Width && pos.Y < Height &&
                   pos.X >= 0 && pos.Y >= 0;
        }

        private IEnumerable<int> IterateCells()
        {
            for (var x = 0; x < Width; x++)
                for (var y = 0; y < Height; y++)
                    yield return this[x, y];
        }
    }
}