code: //==============================================================================
  //	
  //	Copyright (c) 2002-
  //	Authors:
  //	* Vojtech Forejt <vojtech.forejt@cs.ox.ac.uk> (University of Oxford)
  //	
  //------------------------------------------------------------------------------
  //	
  //	This file is part of PRISM.
  //	
  //	PRISM is free software; you can redistribute it and/or modify
  //	it under the terms of the GNU General Public License as published by
  //	the Free Software Foundation; either version 2 of the License, or
  //	(at your option) any later version.
  //	
  //	PRISM is distributed in the hope that it will be useful,
  //	but WITHOUT ANY WARRANTY; without even the implied warranty of
  //	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  //	GNU General Public License for more details.
  //	
  //	You should have received a copy of the GNU General Public License
  //	along with PRISM; if not, write to the Free Software Foundation,
  //	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  //	
  //==============================================================================
  
  package prism;
  
  import java.util.Arrays;
  import java.util.Comparator;
  
  /**
   * A class that allows to compare points w.r.g. a lexicographic order.
   * The order of elements is given by the array {@code dimensionPermutation}
   * passed in the constructor {@link #PermutedLexicographicComparator(int[],boolean[])}.
   * <br>
   * Note that the comparator is only capable of comparing points with equal
   * dimension. This probably violates the specification of the {@link Comparator}
   * class, but it shouldn't be any problem as comparing points of different dimensions
   * makes no sense in our case.
   */
  public class PermutedLexicographicComparator implements Comparator<Point>
  {
  	private int[] permutation;
  	private boolean[] increasing;
  	
  	/**
  	 * Creates a new instance of the comparator.
  	 * @param dimensionPermutation The order of coordinates, the length of
  	 * the array must be equal to the dimension of points to be compared. For example,
  	 * supposing the dimension of points to compare is 3, the array [2,0,1] says
  	 * that the lexicographic order should be used in which the last coordinate
  	 * has the highest priority, and then the first two follow.
  	 * @param increasing if increasing[i] is true, then the ith dimension
  	 * will be used such that the points with the smaller values go first, otherwise they go last
  	 */
  	public PermutedLexicographicComparator(int[] dimensionPermutation, boolean[] increasing) {
  		//check that the array is a valid permutation
  		int[] clone = dimensionPermutation.clone();
  		//TODO check size etc.
  		this.increasing = increasing;
  		Arrays.sort(clone);
  		for(int i = 0; i < clone.length; i++)
  			if (clone[i] != i)
  				throw new IllegalArgumentException("The array is not a valid permutation");
  		this.permutation = dimensionPermutation;
  	}
  
  	@Override
  	public int compare(Point o1, Point o2)
  	{
  		//check if the input is allowed;
  		if (o1.getDimension() > permutation.length
  				|| o2.getDimension() > permutation.length)
  			throw new ClassCastException("The dimension of the point is greater that comparator's dimension");
  		
  		if(o1.isCloseTo(o2))
  			return 0;
  		
  		return compare(o1,o2,0);
  	}
  	
  	/**
  	 * Compares two points, starting with the coordinate with the
  	 * {@code i}-th highest priority. 
  	 * @param o1
  	 * @param o2
  	 * @param i
  	 * @return
  	 */
  	protected int compare(Point o1, Point o2, int i)
  	{
  		int dim = this.permutation[i];
  		if ( o1.getCoord(dim) < o2.getCoord(dim))
  			return (increasing[dim]) ? -1 : 1;
  		else if (o1.getCoord(dim) > o2.getCoord(dim))
  			return (increasing[dim]) ? 1 : -1;
  		else return compare(o1, o2, i+1);
  	}
  }
  