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GraphHelper.java

/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Lead:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2004, 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.
 */
/* ----------------
 * GraphHelper.java
 * ----------------
 * (C) Copyright 2003, by Barak Naveh and Contributors.
 *
 * Original Author:  Barak Naveh
 * Contributor(s):   Mikael Hansen
 *
 * $Id: GraphHelper.java,v 1.11 2005/04/23 08:25:17 perfecthash Exp $
 *
 * Changes
 * -------
 * 10-Jul-2003 : Initial revision (BN);
 * 06-Nov-2003 : Change edge sharing semantics (JVS);
 *
 */
package org._3pq.jgrapht;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org._3pq.jgrapht.edge.DirectedEdge;
import org._3pq.jgrapht.graph.AsUndirectedGraph;

/**
 * A collection of utilities to assist the working with graphs.
 *
 * @author Barak Naveh
 *
 * @since Jul 31, 2003
 */
00056 public final class GraphHelper {
    private GraphHelper(  ) {} // ensure non-instantiability.

    /**
     * Creates a new edge and adds it to the specified graph similarly to the
     * {@link Graph#addEdge(Object, Object)} method.
     *
     * @param g the graph for which the edge to be added.
     * @param sourceVertex source vertex of the edge.
     * @param targetVertex target vertex of the edge.
     * @param weight weight of the edge.
     *
     * @return The newly created edge if added to the graph, otherwise
     *         <code>null</code>.
     *
     * @see Graph#addEdge(Object, Object)
     */
00073     public static Edge addEdge( Graph g, Object sourceVertex,
        Object targetVertex, double weight ) {
        EdgeFactory ef = g.getEdgeFactory(  );
        Edge        e = ef.createEdge( sourceVertex, targetVertex );

        // we first create the edge and set the weight to make sure that 
        // listeners will see the correct weight upon addEdge.
        e.setWeight( weight );

        return g.addEdge( e ) ? e : null;
    }


    /**
     * Adds the specified edge to the specified graph including its vertices.
     * If any of the vertices of the specified edge are not already in the
     * graph they are also added (before the edge is added).
     *
     * @param g the graph for which the specified edge to be added.
     * @param e the edge to be added to the graph (including its vertices).
     *
     * @return <code>true</code> if and only if the specified edge was not
     *         already contained in the graph.
     */
00097     public static boolean addEdgeWithVertices( Graph g, Edge e ) {
        g.addVertex( e.getSource(  ) );
        g.addVertex( e.getTarget(  ) );

        return g.addEdge( e );
    }


    /**
     * Adds the specified source and target vertices to the graph, if not
     * already included, and creates a new edge and adds it to the specified
     * graph similarly to the {@link Graph#addEdge(Object, Object)} method.
     *
     * @param g the graph for which the specified edge to be added.
     * @param sourceVertex source vertex of the edge.
     * @param targetVertex target vertex of the edge.
     *
     * @return The newly created edge if added to the graph, otherwise
     *         <code>null</code>.
     */
00117     public static Edge addEdgeWithVertices( Graph g, Object sourceVertex,
        Object targetVertex ) {
        g.addVertex( sourceVertex );
        g.addVertex( targetVertex );

        return g.addEdge( sourceVertex, targetVertex );
    }


    /**
     * Adds the specified source and target vertices to the graph, if not
     * already included, and creates a new weighted edge and adds it to the
     * specified graph similarly to the {@link Graph#addEdge(Object, Object)}
     * method.
     *
     * @param g the graph for which the specified edge to be added.
     * @param sourceVertex source vertex of the edge.
     * @param targetVertex target vertex of the edge.
     * @param weight weight of the edge.
     *
     * @return The newly created edge if added to the graph, otherwise
     *         <code>null</code>.
     */
00140     public static Edge addEdgeWithVertices( Graph g, Object sourceVertex,
        Object targetVertex, double weight ) {
        g.addVertex( sourceVertex );
        g.addVertex( targetVertex );

        return addEdge( g, sourceVertex, targetVertex, weight );
    }


    /**
     * Adds all the vertices and all the edges of the specified source graph to
     * the specified destination graph. First all vertices of the source graph
     * are added to the destination graph. Then every edge of the source graph
     * is added to the destination graph. This method returns
     * <code>true</code> if the destination graph has been modified as a
     * result of this operation, otherwise it returns <code>false</code>.
     * 
     * <p>
     * The behavior of this operation is undefined if any of the specified
     * graphs is modified while operation is in progress.
     * </p>
     *
     * @param destination the graph to which vertices and edges are added.
     * @param source the graph used as source for vertices and edges to add.
     *
     * @return <code>true</code> if and only if the destination graph has been
     *         changed as a result of this operation.
     */
00168     public static boolean addGraph( Graph destination, Graph source ) {
        boolean modified = destination.addAllVertices( source.vertexSet(  ) );
        modified |= destination.addAllEdges( source.edgeSet(  ) );

        return modified;
    }


    /**
     * Adds all the vertices and all the edges of the specified source digraph
     * to the specified destination digraph, reversing all of the edges.
     * 
     * <p>
     * The behavior of this operation is undefined if any of the specified
     * graphs is modified while operation is in progress.
     * </p>
     *
     * @param destination the graph to which vertices and edges are added.
     * @param source the graph used as source for vertices and edges to add.
     */
00188     public static void addGraphReversed( DirectedGraph destination,
        DirectedGraph source ) {
        destination.addAllVertices( source.vertexSet(  ) );

        Iterator edgesIter = source.edgeSet(  ).iterator(  );

        while( edgesIter.hasNext(  ) ) {
            DirectedEdge edge         = (DirectedEdge) edgesIter.next(  );
            DirectedEdge reversedEdge =
                new DirectedEdge( edge.getTarget(  ), edge.getSource(  ) );
            destination.addEdge( reversedEdge );
        }
    }


    /**
     * Returns a list of vertices that are the neighbors of a specified vertex.
     * If the graph is a multigraph vertices may appear more than once in the
     * returned list.
     *
     * @param g the graph to look for neighbors in.
     * @param vertex the vertex to get the neighbors of.
     *
     * @return a list of the vertices that are the neighbors of the specified
     *         vertex.
     */
00214     public static List neighborListOf( Graph g, Object vertex ) {
        List neighbors = new ArrayList(  );

        for( Iterator i = g.edgesOf( vertex ).iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );
            neighbors.add( e.oppositeVertex( vertex ) );
        }

        return neighbors;
    }


    /**
     * Returns a list of vertices that are the predecessors of a specified
     * vertex. If the graph is a multigraph, vertices may appear more than
     * once in the returned list.
     *
     * @param g the graph to look for predecessors in.
     * @param vertex the vertex to get the predecessors of.
     *
     * @return a list of the vertices that are the predecessors of the
     *         specified vertex.
     */
00237     public static List predecessorListOf( DirectedGraph g, Object vertex ) {
        List predecessors = new ArrayList(  );
        List edges = g.incomingEdgesOf( vertex );

        for( Iterator i = edges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );
            predecessors.add( e.oppositeVertex( vertex ) );
        }

        return predecessors;
    }


    /**
     * Returns a list of vertices that are the successors of a specified
     * vertex. If the graph is a multigraph vertices may appear more than once
     * in the returned list.
     *
     * @param g the graph to look for successors in.
     * @param vertex the vertex to get the successors of.
     *
     * @return a list of the vertices that are the successors of the specified
     *         vertex.
     */
00261     public static List successorListOf( DirectedGraph g, Object vertex ) {
        List successors = new ArrayList(  );
        List edges = g.outgoingEdgesOf( vertex );

        for( Iterator i = edges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );
            successors.add( e.oppositeVertex( vertex ) );
        }

        return successors;
    }


    /**
     * Returns an undirected view of the specified graph. If the specified
     * graph is directed, returns an undirected view of it. If the specified
     * graph is undirected, just returns it.
     *
     * @param g the graph for which an undirected view to be returned.
     *
     * @return an undirected view of the specified graph, if it is directed, or
     *         or the specified graph itself if it is undirected.
     *
     * @throws IllegalArgumentException if the graph is neither DirectedGraph
     *         nor UndirectedGraph.
     *
     * @see AsUndirectedGraph
     */
00289     public static UndirectedGraph undirectedGraph( Graph g ) {
        if( g instanceof DirectedGraph ) {
            return new AsUndirectedGraph( (DirectedGraph) g );
        }
        else if( g instanceof UndirectedGraph ) {
            return (UndirectedGraph) g;
        }
        else {
            throw new IllegalArgumentException( 
                "Graph must be either DirectedGraph or UndirectedGraph" );
        }
    }
}

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