commons-graph/src/java/org/apache/commons/graph/DFS.java

package org.apache.commons.graph;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    distribution.
 *
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 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
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 * 5. Products derived from this software may not be called "Apache",
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 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import org.apache.commons.graph.visitor.Visitor;

/**
 * Visit graph with depth first search and mark discovery and finishing time in all
 * vertices.
 *
 * @version $Id: DFS.java,v 1.2 2001/11/29 14:17:33 jvanzyl Exp $
 * @author  <A HREF="http://www.inf.fu-berlin.de/~dahm">M. Dahm</A>
 */
public class DFS extends TraversalOrder {
  /**
   * Depth first search algorithm.
   *
   * @param v visitor object to apply when discovering and finishing a vertex or edge
   */
  public DFS(Visitor v) {
    super(v);
  }

  /**
   * Depth first search algorithm.
   *
   * @param v visitor object to apply when discovering and finishing a vertex or edge
   * @param traverse_all traverse the complete graph or stop after finishing all nodes reachable
   * from the start
   */
  public DFS(Visitor v, boolean traverse_all) {
    super(v, traverse_all);
  }

  /**
   * Run depth first search (DFS) algorithm.
   *
   * @param g graph to traverse
   * @param start vertex to start at (or null, starts at some vertex then)
   */
  public void start(Graph g, Vertex start) {
    int      size     = g.getNoVertices();
    Vertex[] vertices = g.getVertexArray();

    graph = g;
    
    visitor.discoverGraph(g);

    /* Initially mark all vertices as WHITE
     */
    for(int i=0; i < size; i++)
      vertices[i].setColor(WHITE);

    if(start != null && g.contains(start)) // Start DFS at (white) start vertex
      DFS_Visit(start);

    if(traverse_complete_graph) {
      for(int i=0; (i < size) && !stopped; i++) {
	Vertex v = vertices[i];
	
	if(v.getColor() == WHITE) // Unvisited vertex?
	  DFS_Visit(v);
      }
    }

    visitor.finishGraph(g);
  }

  private final void DFS_Visit(Vertex u) {
    u.setColor(GRAY);      // Mark as visited
    visitor.discoverVertex(u);

    Vertex[] vertices = graph.getVertexArray(u); // Get adjacent vertices
    Edge[]   edges    = graph.getEdgeArray(u);   // and edges
    int      size     = vertices.length;
    //System.out.println(java.util.Arrays.asList(edges));

    for(int i=0; (i < size) && !stopped; i++) {     // Explore all edges
      visitor.discoverEdge(edges[i]);

      Vertex v = vertices[i];

      if(v.getColor() == WHITE)
	DFS_Visit(v);

      visitor.finishEdge(edges[i]);
    }

    u.setColor(BLACK);  // Mark as finished
    visitor.finishVertex(u);
  }
}