Spiral box on C# (see http://habrahabr.ru/post/210796/)

gistfile1.cs

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

namespace Box
{
    public interface IAsset
    {
        void Accept(IVisitor visitor);
    }

    public class MyBox : IAsset
    {
        public int[,] Arr;
        public int Size;

        public MyBox(int size)
        {
            this.Size = size;
            Arr = new int[size, size];
        }

        public void Accept(IVisitor visitor)
        {
            visitor.Visit(this);
        }

        public override string ToString()
        {
            string s = "";
            for (int i = 0; i < Size; i++)
            {
                for(int j = 0; j < Size; j++)
                {
                    s += (" " + String.Format("{0:D2}", Arr[j, i]) + " ").Replace(" 00 ", " __ ");
                }
                s += "\r\n";
            }
            return s;
        }
    }

    public interface IVisitor
    {
        void Visit(MyBox box);
    }

    public class MyVisitor : IVisitor
    {
        public enum Directions { Left, Right, Up, Down }
        
        public class Rules
        {
            private int index = 0;

            public Directions CurrentDirection
            {
                get
                {
                    return rules[index];
                }
            }

            private List<Directions> rules = new List<Directions>
            {
                Directions.Right,
                Directions.Down,
                Directions.Left,
                Directions.Up
            };
            
            public void SwitchToNext()
            {
                index++;
                if (index > 3)
                    index = 0;
            }
        }

        private Rules rules = new Rules();

        private bool isObstacle(MyBox box, Directions direction, int x, int y)
        {
            switch(direction)
            {
                case Directions.Right:
                    if (x + 1 >= box.Size)
                        return true;
                    return box.Arr[x + 1, y] != 0;

                case Directions.Down:
                    if (y + 1 >= box.Size)
                        return true;
                    return box.Arr[x, y + 1] != 0;

                case Directions.Left:
                    if (x - 1 < 0)
                        return true;
                    return box.Arr[x - 1, y] != 0;

                case Directions.Up:
                    if (y - 1 < 0)
                        return true;
                    return box.Arr[x, y - 1] != 0;

                default:
                    throw new NotSupportedException();
            }
        }

        public void Visit(MyBox box)
        {
            int x = -1;
            int y = 0;
            int value = 1;

            while(value < box.Size * box.Size + 1)
            {
                if(isObstacle(box, rules.CurrentDirection, x, y))
                    rules.SwitchToNext();

                switch(rules.CurrentDirection)
                {
                    case Directions.Right:
                        x++;
                        break;
                    case Directions.Down:
                        y++;
                        break;
                    case Directions.Left:
                        x--;
                        break;
                    case Directions.Up:
                        y--;
                        break;
                }

                box.Arr[x, y] = value;
                value++;
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Type the size (enter for 8): ");
            
            string str = Console.ReadLine();
            if (String.IsNullOrWhiteSpace(str))
                str = "8";
            
            int size = Int32.Parse(str);

            IVisitor visitor = new MyVisitor();
            MyBox box = new MyBox(size);
            box.Accept(visitor);

            Console.WriteLine(box);
        }
    }
}