Transpose.java

/*
 * Generic graph library
 * Copyright (C) 2000,2003,2004 University of Maryland
 *
 * 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
 */

// $Revision: 1.15 $

package edu.umd.cs.findbugs.graph;

import java.util.IdentityHashMap;
import java.util.Iterator;

/**
 * Algorithm to transpose a graph.
 */
public class Transpose<GraphType extends Graph<EdgeType, VertexType>, EdgeType extends GraphEdge<EdgeType, VertexType>, VertexType extends GraphVertex<VertexType>> {

    private IdentityHashMap<VertexType, VertexType> m_origToTransposeMap;

    private IdentityHashMap<VertexType, VertexType> m_transposeToOrigMap;

    /**
     * Constructor.
     */
    public Transpose() {
        m_origToTransposeMap = new IdentityHashMap<VertexType, VertexType>();
        m_transposeToOrigMap = new IdentityHashMap<VertexType, VertexType>();
    }

    /**
     * Transpose a graph. Note that the original graph is not modified; the new
     * graph and its vertices and edges are new objects.
     * 
     * @param orig
     *            the graph to transpose
     * @param toolkit
     *            a GraphToolkit to be used to create the transposed Graph
     * @return the transposed Graph
     */
    public GraphType transpose(GraphType orig, GraphToolkit<GraphType, EdgeType, VertexType> toolkit) {

        GraphType trans = toolkit.createGraph();

        // For each vertex in original graph, create an equivalent
        // vertex in the transposed graph,
        // ensuring that vertex labels in the transposed graph
        // match vertex labels in the original graph
        for (Iterator<VertexType> i = orig.vertexIterator(); i.hasNext();) {
            VertexType v = i.next();

            // Make a duplicate of original vertex
            // (Ensuring that transposed graph has same labeling as original)
            VertexType dupVertex = toolkit.duplicateVertex(v);
            dupVertex.setLabel(v.getLabel());
            trans.addVertex(v);

            // Keep track of correspondence between equivalent vertices
            m_origToTransposeMap.put(v, dupVertex);
            m_transposeToOrigMap.put(dupVertex, v);
        }
        trans.setNumVertexLabels(orig.getNumVertexLabels());

        // For each edge in the original graph, create a reversed edge
        // in the transposed graph
        for (Iterator<EdgeType> i = orig.edgeIterator(); i.hasNext();) {
            EdgeType e = i.next();

            VertexType transSource = m_origToTransposeMap.get(e.getTarget());
            VertexType transTarget = m_origToTransposeMap.get(e.getSource());

            EdgeType dupEdge = trans.createEdge(transSource, transTarget);
            dupEdge.setLabel(e.getLabel());

            // Copy auxiliary information for edge
            toolkit.copyEdge(e, dupEdge);
        }
        trans.setNumEdgeLabels(orig.getNumEdgeLabels());

        return trans;

    }

    /**
     * Get the vertex in the transposed graph which corresponds to the given
     * vertex in the original graph.
     * 
     * @param v
     *            the vertex in the original graph
     * @return the equivalent vertex in the transposed graph
     */
    public VertexType getTransposedGraphVertex(VertexType v) {
        return m_origToTransposeMap.get(v);
    }

    /**
     * Get the vertex in the original graph which corresponds to the given
     * vertex in the transposed graph.
     * 
     * @param v
     *            the vertex in the transposed graph
     * @return the equivalent vertex in the original graph
     */
    public VertexType getOriginalGraphVertex(VertexType v) {
        return m_transposeToOrigMap.get(v);
    }

}

// vim:ts=4