C#

<br />
foreach(Point a in shorter){<br />
    foreach(Point b in longer){<br />
        if(a.Sum != b.Sum) break;<br />
            if(a == b)<br />
                union.Add(a); break;<br />
    }<br />
}<br />

Zilo(svk) wrote:

I've created my own Point2D struct because accessing fields directly without Properties is much faster when considering a lot of iterations.

Zilo(svk) wrote:

I don't understand what's O(n2)

using System.Drawing;
using System.Diagnostics;
using System;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            const int count = 100000000;
            int x = 0;
            Stopwatch watch = new Stopwatch();

            Console.WriteLine("Starting Point iteration");
            Point p = new Point(1, 1);
            Point2D p2d = new Point2D(1, 1);
            watch.Start();            
            for (int i = 0; i < count; i++)
            { 
                x = p.X + p.Y;
            }
            watch.Stop();
            Console.WriteLine("Point iteration took {0} mls\n\r", watch.ElapsedMilliseconds);
            watch.Reset();
            Console.WriteLine("Starting Point2D iteration");
            watch.Start();     
            for (int i = 0; i < count; i++)
            {               
                x = p2d.X + p2d.Y;
            }
            watch.Stop();
            Console.WriteLine("Point2D iteration took {0} mls", watch.ElapsedMilliseconds);

            Console.ReadKey();
        }

        struct Point2D
        {
            public int X, Y;

            public Point2D(int x, int y)
            {
                this.X = x;
                this.Y = y;
            }
        }
    }   
}