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/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh (http://sourceforge.net/users/barak_naveh)
*
* (C) Copyright 2003-2007, by Barak Naveh and Contributors.
*
* This library is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software Foundation,
* Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
*/
/* ---------------------------
* VertexDegreeComparator.java
* ---------------------------
* (C) Copyright 2003-2007, by Linda Buisman and Contributors.
*
* Original Author: Linda Buisman
* Contributor(s): Christian Hammer
*
* $Id: VertexDegreeComparator.java 568 2007-09-30 00:12:18Z perfecthash $
*
* Changes
* -------
* 06-Nov-2003 : Initial revision (LB);
* 07-Jun-2005 : Made generic (CH);
*
*/
package org.jgrapht.alg.util;
import org.jgrapht.*;
/**
* Compares two vertices based on their degree.
*
* Used by greedy algorithms that need to sort vertices by their degree. Two
* vertices are considered equal if their degrees are equal.
*
* @author Linda Buisman
* @since Nov 6, 2003
*/
public class VertexDegreeComparator
implements java.util.Comparator
{
//~ Instance fields --------------------------------------------------------
/**
* The graph that contains the vertices to be compared.
*/
private UndirectedGraph graph;
/**
* The sort order for vertex degree. true for ascending degree
* order (smaller degrees first), false for descending.
*/
private boolean ascendingOrder;
//~ Constructors -----------------------------------------------------------
/**
* Creates a comparator for comparing the degrees of vertices in the
* specified graph. The comparator compares in ascending order of degrees
* (lowest first).
*
* @param g graph with respect to which the degree is calculated.
*/
public VertexDegreeComparator(UndirectedGraph g)
{
this(g, true);
}
/**
* Creates a comparator for comparing the degrees of vertices in the
* specified graph.
*
* @param g graph with respect to which the degree is calculated.
* @param ascendingOrder true - compares in ascending order of degrees
* (lowest first), false - compares in descending order of degrees (highest
* first).
*/
public VertexDegreeComparator(
UndirectedGraph g,
boolean ascendingOrder)
{
graph = g;
this.ascendingOrder = ascendingOrder;
}
//~ Methods ----------------------------------------------------------------
/**
* Compare the degrees of v1 and v2, taking into
* account whether ascending or descending order is used.
*
* @param v1 the first vertex to be compared.
* @param v2 the second vertex to be compared.
*
* @return -1 if v1 comes before v2, +1 if
* v1 comes after v2, 0 if equal.
*/
public int compare(V v1, V v2)
{
int degree1 = graph.degreeOf(v1);
int degree2 = graph.degreeOf(v2);
if (((degree1 < degree2) && ascendingOrder)
|| ((degree1 > degree2) && !ascendingOrder))
{
return -1;
} else if (
((degree1 > degree2) && ascendingOrder)
|| ((degree1 < degree2) && !ascendingOrder))
{
return 1;
} else {
return 0;
}
}
}
// End VertexDegreeComparator.java