Genericki Klasteri

import java.util.*;

/**
 * January 2016 Exam problem 2
 */
public class ClusterTest {
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    Cluster<Point2D> cluster = new Cluster<>();
    int n = scanner.nextInt();
    scanner.nextLine();
    for (int i = 0; i < n; ++i) {
      String line = scanner.nextLine();
      String[] parts = line.split(" ");
      long id = Long.parseLong(parts[0]);
      float x = Float.parseFloat(parts[1]);
      float y = Float.parseFloat(parts[2]);
      cluster.addItem(new Point2D(id, x, y));
    }
    int id = scanner.nextInt();
    int top = scanner.nextInt();
    cluster.near(id, top);
    scanner.close();
  }
}

// your code here
abstract class Element<T>
{
	long id;

	abstract long getId();

	abstract double getDistance(T item);
}

class Cluster<T extends Element<T>>
{
	Map<Long, T> elements;

	public Cluster()
	{
		elements = new HashMap<>();
	}

	public void addItem(T element)
	{
		elements.put(element.getId(), element);
	}

	public void near(long id, int top)
	{
		List<T> list = new ArrayList<>(elements.values());
		T el = elements.get(id);

		Collections.sort(list, new Comparator<T>() {

			@Override
			public int compare(T o1, T o2) {
				// TODO Auto-generated method stub
				return Double.compare(o1.getDistance(el), o2.getDistance(el));
			}


		});

		for(int i=1; i<=top; i++)
		{
			System.out.printf("%d. %d -> %.3f\n", i, list.get(i).getId(), list.get(i).getDistance(el));
		}


	}
}

class Point2D extends Element<Point2D>
{
	long id;
	float x,y;

	Point2D(long id, float x, float y)
	{
		this.id = id;
		this.x = x;
		this.y = y;
	}

	@Override
	long getId() {
		// TODO Auto-generated method stub
		return id;
	}

	@Override
	double getDistance(Point2D item) {
		// TODO Auto-generated method stub
		return Math.sqrt(Math.pow(x-item.x, 2) + Math.pow(y-item.y, 2));
	}


}