org.jgrapht.alg.util.VertexDegreeComparator Maven / Gradle / Ivy
/* ==========================================
* 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 2003-2008, by Barak Naveh and Contributors.
*
* This program and the accompanying materials are dual-licensed under
* either
*
* (a) the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation, or (at your option) any
* later version.
*
* or (per the licensee's choosing)
*
* (b) the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation.
*/
/* ---------------------------
* VertexDegreeComparator.java
* ---------------------------
* (C) Copyright 2003-2008, by Linda Buisman and Contributors.
*
* Original Author: Linda Buisman
* Contributor(s): Christian Hammer
*
* $Id$
*
* 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
{
/**
* 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;
/**
* 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;
}
/**
* 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.
*/
@Override 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