/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2002-2008, Open Source Geospatial Foundation (OSGeo)
*
* 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;
* version 2.1 of the License.
*
* 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.
*/
package org.geotools.graph.path;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import org.geotools.graph.structure.Edge;
import org.geotools.graph.structure.Node;
/**
*
* Represents a cycle in a graph. A <B>cycle</B> C is defined as a closed walk
* of size n in which nodes 1 through n-1 form a path.
*
* @author Justin Deoliveira, Refractions Research Inc, jdeolive@refractions.net
*
*
* @source $URL$
*/
public class Cycle extends Walk {
//TODO: DOCUMENT ME!
public Cycle(Collection nodes) {
super(nodes);
}
/**
* Tests if the cycle is valid. A valid cycle satisfies two conditions: <BR>
* <BR>
* 1. Each pair of adjacent nodes share an edge.<BR>
* 2. The first and last nodes share an edge.
* 3. The only node repetition is the first and last nodes.
*/
public boolean isValid() {
if (super.isValid()) {
//ensure first and last nodes are same
if (isClosed()) {
//ensure no node repetitions except for first and last
return(new HashSet(this).size() == size()-1);
}
}
return(false);
}
protected List buildEdges() {
List edges = super.buildEdges();
//get the edge between the first and last nodes
Node first = (Node)get(0);
Node last = (Node)get(size()-1);
Edge e = first.getEdge(last);
if (e != null) {
edges.add(e);
return(edges);
}
return(null);
}
}