using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    static int CountIslands(IEnumerable<Tuple<int, int>> points)

    {

        var offsets = new int[8,2] { {-1,-1}, {-1,0}, {-1,1}, {0,-1}, {0,1}, {1,-1}, {1,0}, {1,1} };

        var pointTable = new HashSet<Tuple<int, int>>(points);

        var stack = new Stack<Tuple<int, int>>();

        var islandCount = 0;

        while (pointTable.Count > 0)

        {

            stack.Push(pointTable.First());

            while (stack.Count() > 0)

            {

                var p = stack.Pop();

                if(pointTable.Remove(p))

                {

                    Console.Write(p);

                    for(int i = 0; i < 8; i++)

                    {

                        stack.Push(Tuple.Create(p.Item1 + offsets[i,0], p.Item2 + offsets[i,1]));

                    }

                }

            }   

​

            Console.WriteLine();

            islandCount++;

        }

​

        return islandCount;

    }

​

    public static void Main()

    {

        var points = new List<Tuple<int, int>>();

        points.Add(Tuple.Create(19,9));

        points.Add(Tuple.Create(11, 11));

        points.Add(Tuple.Create(10, 10));

        points.Add(Tuple.Create(10, 10));

        points.Add(Tuple.Create(11, 10));

        points.Add(Tuple.Create(20, 10));

        points.Add(Tuple.Create(21, 12));

        Console.WriteLine(CountIslands(points) + " Islands");

    }

}