// An array of N integer (x,y) pairs specifies the points on the plain.

// Find the path consisting of n-1 line segments at most

// that goes through all points and has no self-intersections.

// Print coordinates of original points along that path. Time is O(N log N).

using System;

​

public class Program

{

    public static void Main()

    {

        Point [] points = new []

        { 

            new Point{ X=0,Y=0},

            new Point{ X=0,Y=2},

            new Point{ X=4,Y=5},

            new Point{ X=3,Y=0},

            new Point{ X=5,Y=2},

            new Point{ X=0,Y=6}

        };

​

        Array.Sort(points, ComparePoint);

        Console.WriteLine("No Self interaction sequence (X,Y) :");

        foreach (Point pt in points)

        {

            Console.WriteLine(pt.X + "," + pt.Y);

        }

    }

    // Compares 2 points lexicographically

    static int ComparePoint(Point a, Point b)

    {

        int byY = a.Y.CompareTo(b.Y);

        if (0 != byY)

            return byY;

        return a.X.CompareTo(b.X);

    }

    public class Point

    {

        public int X;

        public int Y;

    }

}