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Subgraph.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.
 */
/* -------------
 * Subgraph.java
 * -------------
 * (C) Copyright 2003-2004, by Barak Naveh and Contributors.
 *
 * Original Author:  Barak Naveh
 * Contributor(s):   -
 *
 * $Id: Subgraph.java,v 1.19 2005/05/25 00:38:37 perfecthash Exp $
 *
 * Changes
 * -------
 * 24-Jul-2003 : Initial revision (BN);
 * 26-Jul-2003 : Accurate constructors to avoid casting problems (BN);
 * 10-Aug-2003 : Adaptation to new event model (BN);
 * 23-Oct-2003 : Allowed non-listenable graph as base (BN);
 * 07-Feb-2004 : Enabled serialization (BN);
 * 20-Mar-2004 : Cancelled verification of element identity to base graph (BN);
 * 21-Sep-2004 : Added induced subgraph
 *
 */
package org._3pq.jgrapht.graph;

import java.io.Serializable;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import org._3pq.jgrapht.DirectedGraph;
import org._3pq.jgrapht.Edge;
import org._3pq.jgrapht.EdgeFactory;
import org._3pq.jgrapht.Graph;
import org._3pq.jgrapht.ListenableGraph;
import org._3pq.jgrapht.UndirectedGraph;
import org._3pq.jgrapht.event.GraphEdgeChangeEvent;
import org._3pq.jgrapht.event.GraphListener;
import org._3pq.jgrapht.event.GraphVertexChangeEvent;

/**
 * A subgraph is a graph that has a subset of vertices and a subset of edges
 * with respect to some base graph. More formally, a subgraph G(V,E) that is
 * based on a base graph Gb(Vb,Eb) satisfies the following <b><i>subgraph
 * property</i></b>: V is a subset of Vb and E is a subset of Eb. Other than
 * this property, a subgraph is a graph with any respect and fully complies
 * with the <code>Graph</code> interface.
 * 
 * <p>
 * If the base graph is a {@link org._3pq.jgrapht.ListenableGraph}, the
 * subgraph listens on the base graph and guarantees the subgraph property. If
 * an edge or a vertex is removed from the base graph, it is automatically
 * removed from the subgraph. Subgraph listeners are informed on such removal
 * only if it results in a cascaded removal from the subgraph. If the subgraph
 * has been created as an induced subgraph it also keeps track of edges being
 * added to its vertices. If  vertices are added to the base graph, the
 * subgraph remains unaffected.
 * </p>
 * 
 * <p>
 * If the base graph is <i>not</i> a ListenableGraph, then the subgraph
 * property cannot be guaranteed. If edges or vertices are removed from the
 * base graph, they are <i>not</i> removed from the subgraph.
 * </p>
 * 
 * <p>
 * Modifications to Subgraph are allowed as long as the subgraph property is
 * maintained. Addition of vertices or edges are allowed as long as they also
 * exist in the base graph. Removal of vertices or edges is always allowed.
 * The base graph is <i>never</i> affected by any modification made to the
 * subgraph.
 * </p>
 * 
 * <p>
 * A subgraph may provide a "live-window" on a base graph, so that changes made
 * to its vertices or edges are immediately reflected in the base graph, and
 * vice versa. For that to happen, vertices and edges added to the subgraph
 * must be <i>identical</i> (that is, reference-equal and not only
 * value-equal) to their respective ones in the base graph. Previous versions
 * of this class enforced such identity, at a severe performance cost.
 * Currently it is no longer enforced. If you want to achieve a "live-window"
 * functionality, your safest tactics would be to NOT override the
 * <code>equals()</code>methods of your vertices and edges. If you use a class
 * that has already overridden the <code>equals()</code> method, such as
 * <code>String</code>, than you can use a wrapper around it, or else use it
 * directly but exercise a great care to avoid having different-but-equal
 * instances in the subgraph and the base graph.
 * </p>
 * 
 * <p>
 * This graph implementation guarantees deterministic vertex and edge set
 * ordering (via {@link LinkedHashSet}).
 * </p>
 *
 * @author Barak Naveh
 *
 * @see org._3pq.jgrapht.Graph
 * @see java.util.Set
 * @since Jul 18, 2003
 */
00126 public class Subgraph extends AbstractGraph implements Serializable {
    private static final String NO_SUCH_EDGE_IN_BASE =
        "no such edge in base graph";
    private static final String NO_SUCH_VERTEX_IN_BASE =
        "no such vertex in base graph";

    //
    Set m_edgeSet   = new LinkedHashSet(  ); // friendly to improve performance
    Set m_vertexSet = new LinkedHashSet(  ); // friendly to improve performance

    // 
    private transient Set m_unmodifiableEdgeSet   = null;
    private transient Set m_unmodifiableVertexSet = null;
    private Graph         m_base;
    private boolean       m_isInduced             = false;
    private boolean       m_verifyIntegrity       = true;

    /**
     * Creates a new Subgraph.
     *
     * @param base the base (backing) graph on which the subgraph will be
     *        based.
     * @param vertexSubset vertices to include in the subgraph. If
     *        <code>null</code> then all vertices are included.
     * @param edgeSubset edges to in include in the subgraph. If
     *        <code>null</code> then all the edges whose vertices found in the
     *        graph are included.
     */
00154     public Subgraph( Graph base, Set vertexSubset, Set edgeSubset ) {
        super(  );

        m_base = base;

        if( m_base instanceof ListenableGraph ) {
            ( (ListenableGraph) m_base ).addGraphListener( new BaseGraphListener(  ) );
        }

        addVerticesUsingFilter( base.vertexSet(  ), vertexSubset );
        addEdgesUsingFilter( base.edgeSet(  ), edgeSubset );
    }


    /**
     * Creates a new induced Subgraph. The subgraph will keep track of edges
     * being added to its vertex subset as well as deletion of edges and
     * vertices. If base it not listenable, this is identical to the call
     * Subgraph(base, vertexSubset, null) .
     *
     * @param base the base (backing) graph on which the subgraph will be
     *        based.
     * @param vertexSubset vertices to include in the subgraph. If
     *        <code>null</code> then all vertices are included.
     */
00179     public Subgraph( Graph base, Set vertexSubset ) {
        this( base, vertexSubset, null );

        m_isInduced = true;
    }

    /**
     * @see org._3pq.jgrapht.Graph#getAllEdges(Object, Object)
     */
00188     public List getAllEdges( Object sourceVertex, Object targetVertex ) {
        List edges = null;

        if( containsVertex( sourceVertex ) && containsVertex( targetVertex ) ) {
            edges = new ArrayList(  );

            List baseEdges = m_base.getAllEdges( sourceVertex, targetVertex );

            for( Iterator i = baseEdges.iterator(  ); i.hasNext(  ); ) {
                Edge e = (Edge) i.next(  );

                if( m_edgeSet.contains( e ) ) { // add if subgraph also contains it
                    edges.add( e );
                }
            }
        }

        return edges;
    }


    /**
     * @see org._3pq.jgrapht.Graph#getEdge(Object, Object)
     */
00212     public Edge getEdge( Object sourceVertex, Object targetVertex ) {
        List edges = getAllEdges( sourceVertex, targetVertex );

        if( edges == null || edges.isEmpty(  ) ) {
            return null;
        }
        else {
            return (Edge) edges.get( 0 );
        }
    }


    /**
     * @see org._3pq.jgrapht.Graph#getEdgeFactory()
     */
00227     public EdgeFactory getEdgeFactory(  ) {
        return m_base.getEdgeFactory(  );
    }


    /**
     * Sets the the check integrity flag.
     *
     * @param verifyIntegrity
     *
     * @see Subgraph
     * @deprecated method will be deleted in future versions. verifyIntegrity
     *             flag has no effect now.
     */
00241     public void setVerifyIntegrity( boolean verifyIntegrity ) {
        m_verifyIntegrity = verifyIntegrity;
    }


    /**
     * Returns the value of the verifyIntegrity flag.
     *
     * @return the value of the verifyIntegrity flag.
     *
     * @deprecated method will be deleted in future versions.
     */
00253     public boolean isVerifyIntegrity(  ) {
        return m_verifyIntegrity;
    }


    /**
     * @see org._3pq.jgrapht.Graph#addEdge(Object, Object)
     */
00261     public Edge addEdge( Object sourceVertex, Object targetVertex ) {
        assertVertexExist( sourceVertex );
        assertVertexExist( targetVertex );

        if( !m_base.containsEdge( sourceVertex, targetVertex ) ) {
            throw new IllegalArgumentException( NO_SUCH_EDGE_IN_BASE );
        }

        List edges = m_base.getAllEdges( sourceVertex, targetVertex );

        for( Iterator i = edges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );

            if( !containsEdge( e ) ) {
                m_edgeSet.add( e );

                return e;
            }
        }

        return null;
    }


    /**
     * Adds the specified edge to this subgraph.
     *
     * @param e the edge to be added.
     *
     * @return <code>true</code> if the edge was added, otherwise
     *         <code>false</code>.
     *
     * @throws NullPointerException
     * @throws IllegalArgumentException
     *
     * @see Subgraph
     * @see org._3pq.jgrapht.Graph#addEdge(Edge)
     */
00299     public boolean addEdge( Edge e ) {
        if( e == null ) {
            throw new NullPointerException(  );
        }

        if( !m_base.containsEdge( e ) ) {
            throw new IllegalArgumentException( NO_SUCH_EDGE_IN_BASE );
        }

        assertVertexExist( e.getSource(  ) );
        assertVertexExist( e.getTarget(  ) );

        if( containsEdge( e ) ) {
            return false;
        }
        else {
            m_edgeSet.add( e );

            return true;
        }
    }


    /**
     * Adds the specified vertex to this subgraph.
     *
     * @param v the vertex to be added.
     *
     * @return <code>true</code> if the vertex was added, otherwise
     *         <code>false</code>.
     *
     * @throws NullPointerException
     * @throws IllegalArgumentException
     *
     * @see Subgraph
     * @see org._3pq.jgrapht.Graph#addVertex(Object)
     */
00336     public boolean addVertex( Object v ) {
        if( v == null ) {
            throw new NullPointerException(  );
        }

        if( !m_base.containsVertex( v ) ) {
            throw new IllegalArgumentException( NO_SUCH_VERTEX_IN_BASE );
        }

        if( containsVertex( v ) ) {
            return false;
        }
        else {
            m_vertexSet.add( v );

            return true;
        }
    }


    /**
     * @see org._3pq.jgrapht.Graph#containsEdge(Edge)
     */
00359     public boolean containsEdge( Edge e ) {
        return m_edgeSet.contains( e );
    }


    /**
     * @see org._3pq.jgrapht.Graph#containsVertex(Object)
     */
00367     public boolean containsVertex( Object v ) {
        return m_vertexSet.contains( v );
    }


    /**
     * @see UndirectedGraph#degreeOf(Object)
     */
00375     public int degreeOf( Object vertex ) {
        assertVertexExist( vertex );

        // sophisticated way to check runtime class of base ;-)
        ( (UndirectedGraph) m_base ).degreeOf( vertex );

        int degree = 0;

        for( Iterator i = m_base.edgesOf( vertex ).iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );

            if( containsEdge( e ) ) {
                degree++;

                if( e.getSource(  ).equals( e.getTarget(  ) ) ) {
                    degree++;
                }
            }
        }

        return degree;
    }


    /**
     * @see org._3pq.jgrapht.Graph#edgeSet()
     */
00402     public Set edgeSet(  ) {
        if( m_unmodifiableEdgeSet == null ) {
            m_unmodifiableEdgeSet = Collections.unmodifiableSet( m_edgeSet );
        }

        return m_unmodifiableEdgeSet;
    }


    /**
     * @see org._3pq.jgrapht.Graph#edgesOf(Object)
     */
00414     public List edgesOf( Object vertex ) {
        assertVertexExist( vertex );

        ArrayList edges     = new ArrayList(  );
        List      baseEdges = m_base.edgesOf( vertex );

        for( Iterator i = baseEdges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );

            if( containsEdge( e ) ) {
                edges.add( e );
            }
        }

        return edges;
    }


    /**
     * @see DirectedGraph#inDegreeOf(Object)
     */
00435     public int inDegreeOf( Object vertex ) {
        assertVertexExist( vertex );

        int degree = 0;

        for( Iterator i =
                ( (DirectedGraph) m_base ).incomingEdgesOf( vertex ).iterator(  );
                i.hasNext(  ); ) {
            if( containsEdge( (Edge) i.next(  ) ) ) {
                degree++;
            }
        }

        return degree;
    }


    /**
     * @see DirectedGraph#incomingEdgesOf(Object)
     */
00455     public List incomingEdgesOf( Object vertex ) {
        assertVertexExist( vertex );

        ArrayList edges     = new ArrayList(  );
        List      baseEdges =
            ( (DirectedGraph) m_base ).incomingEdgesOf( vertex );

        for( Iterator i = baseEdges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );

            if( containsEdge( e ) ) {
                edges.add( e );
            }
        }

        return edges;
    }


    /**
     * @see DirectedGraph#outDegreeOf(Object)
     */
00477     public int outDegreeOf( Object vertex ) {
        assertVertexExist( vertex );

        int degree = 0;

        for( Iterator i =
                ( (DirectedGraph) m_base ).outgoingEdgesOf( vertex ).iterator(  );
                i.hasNext(  ); ) {
            if( containsEdge( (Edge) i.next(  ) ) ) {
                degree++;
            }
        }

        return degree;
    }


    /**
     * @see DirectedGraph#outgoingEdgesOf(Object)
     */
00497     public List outgoingEdgesOf( Object vertex ) {
        assertVertexExist( vertex );

        ArrayList edges     = new ArrayList(  );
        List      baseEdges =
            ( (DirectedGraph) m_base ).outgoingEdgesOf( vertex );

        for( Iterator i = baseEdges.iterator(  ); i.hasNext(  ); ) {
            Edge e = (Edge) i.next(  );

            if( containsEdge( e ) ) {
                edges.add( e );
            }
        }

        return edges;
    }


    /**
     * @see org._3pq.jgrapht.Graph#removeEdge(Edge)
     */
00519     public boolean removeEdge( Edge e ) {
        return m_edgeSet.remove( e );
    }


    /**
     * @see org._3pq.jgrapht.Graph#removeEdge(Object, Object)
     */
00527     public Edge removeEdge( Object sourceVertex, Object targetVertex ) {
        Edge e = getEdge( sourceVertex, targetVertex );

        return m_edgeSet.remove( e ) ? e : null;
    }


    /**
     * @see org._3pq.jgrapht.Graph#removeVertex(Object)
     */
00537     public boolean removeVertex( Object v ) {
        // If the base graph does NOT contain v it means we are here in 
        // response to removal of v from the base. In such case we don't need 
        // to remove all the edges of v as they were already removed. 
        if( containsVertex( v ) && m_base.containsVertex( v ) ) {
            removeAllEdges( edgesOf( v ) );
        }

        return m_vertexSet.remove( v );
    }


    /**
     * @see org._3pq.jgrapht.Graph#vertexSet()
     */
00552     public Set vertexSet(  ) {
        if( m_unmodifiableVertexSet == null ) {
            m_unmodifiableVertexSet =
                Collections.unmodifiableSet( m_vertexSet );
        }

        return m_unmodifiableVertexSet;
    }


    private void addEdgesUsingFilter( Set edgeSet, Set filter ) {
        Edge    e;
        boolean containsVertices;
        boolean edgeIncluded;

        for( Iterator i = edgeSet.iterator(  ); i.hasNext(  ); ) {
            e     = (Edge) i.next(  );

            containsVertices =
                containsVertex( e.getSource(  ) )
                && containsVertex( e.getTarget(  ) );

            // note the use of short circuit evaluation            
            edgeIncluded = ( filter == null ) || filter.contains( e );

            if( containsVertices && edgeIncluded ) {
                addEdge( e );
            }
        }
    }


    private void addVerticesUsingFilter( Set vertexSet, Set filter ) {
        Object v;

        for( Iterator i = vertexSet.iterator(  ); i.hasNext(  ); ) {
            v = i.next(  );

            // note the use of short circuit evaluation            
            if( filter == null || filter.contains( v ) ) {
                addVertex( v );
            }
        }
    }

    /**
     * An internal listener on the base graph.
     *
     * @author Barak Naveh
     *
     * @since Jul 20, 2003
     */
00604     private class BaseGraphListener implements GraphListener, Serializable {
        /**
         * @see GraphListener#edgeAdded(GraphEdgeChangeEvent)
         */
00608         public void edgeAdded( GraphEdgeChangeEvent e ) {
            if( m_isInduced ) {
                addEdge( e.getEdge(  ) );
            }
        }


        /**
         * @see GraphListener#edgeRemoved(GraphEdgeChangeEvent)
         */
00618         public void edgeRemoved( GraphEdgeChangeEvent e ) {
            Edge edge = e.getEdge(  );

            removeEdge( edge );
        }


        /**
         * @see VertexSetListener#vertexAdded(GraphVertexChangeEvent)
         */
00628         public void vertexAdded( GraphVertexChangeEvent e ) {
            // we don't care
        }


        /**
         * @see VertexSetListener#vertexRemoved(GraphVertexChangeEvent)
         */
00636         public void vertexRemoved( GraphVertexChangeEvent e ) {
            Object vertex = e.getVertex(  );

            removeVertex( vertex );
        }
    }
}

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