net.automatalib.algorithms.graph.scc.TarjanSCCVisitor Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of automata-misc-algorithms Show documentation

This artifact contains several miscellaneous, well-known algorithms, which however are rather specific in their concrete use case and therefore not fit for the AutomataLib Utilities library. Examples include Dijkstra's algorithm for the SSSP problem, the Floyd-Warshall algorithm for the APSP problem and Tarjan's algorithm for finding all strongly-connected components in a graph.

There is a newer version: 0.6.0

Show newest version

/* Copyright (C) 2013 TU Dortmund
 * This file is part of AutomataLib, http://www.automatalib.net/.
 * 
 * AutomataLib is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 3.0 as published by the Free Software Foundation.
 * 
 * AutomataLib 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 AutomataLib; if not, see
 * http://www.gnu.de/documents/lgpl.en.html.
 */
package net.automatalib.algorithms.graph.scc;

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

import net.automatalib.commons.util.Holder;
import net.automatalib.commons.util.mappings.MutableMapping;
import net.automatalib.graphs.Graph;
import net.automatalib.util.graphs.traversal.GraphTraversalAction;
import net.automatalib.util.graphs.traversal.GraphTraversalVisitor;


/**
 * Depth-first traversal visitor realizing Tarjan's algorithm for finding all
 * strongly-connected components (SCCs) in a graph.
 * 
 * @author Malte Isberner 
 *
 * @param  node class
 * @param  edge class
 */
public class TarjanSCCVisitor implements
		GraphTraversalVisitor {
	
	private static final int NODE_FINISHED = -1;
	
	private int counter = 0;
	private final MutableMapping records;
	private final List currentScc = new ArrayList<>();
	private final SCCListener listener;
	
	/**
	 * Constructor.
	 * @param graph the graph
	 * @param listener the SCC listener to use, may not be null
	 */
	public TarjanSCCVisitor(Graph graph, SCCListener listener) {
		records = graph.createStaticNodeMapping();
		this.listener = listener;
	}
	
	/*
	 * (non-Javadoc)
	 * @see net.automatalib.util.graphs.traversal.GraphTraversalVisitor#processInitial(java.lang.Object, net.automatalib.commons.util.Holder)
	 */
	@Override
	public GraphTraversalAction processInitial(N initialNode, Holder outData) {
		outData.value = createRecord();
		return GraphTraversalAction.EXPLORE;
	}
	
	/*
	 * (non-Javadoc)
	 * @see net.automatalib.util.graphs.traversal.GraphTraversalVisitor#startExploration(java.lang.Object, java.lang.Object)
	 */
	@Override
	public boolean startExploration(N node, TarjanSCCRecord data) {
		records.put(node, data);
		return true;
	}
	
	/*
	 * (non-Javadoc)
	 * @see net.automatalib.util.graphs.traversal.GraphTraversalVisitor#finishExploration(java.lang.Object, java.lang.Object)
	 */
	@Override
	public void finishExploration(N node, TarjanSCCRecord data) {
		currentScc.add(node);
		if(data.lowLink == data.number) {
			listener.foundSCC(currentScc);
			currentScc.clear();
		}
		data.lowLink = NODE_FINISHED;
	}
	
	/*
	 * (non-Javadoc)
	 * @see net.automatalib.util.graphs.traversal.GraphTraversalVisitor#processEdge(java.lang.Object, java.lang.Object, java.lang.Object, java.lang.Object, net.automatalib.commons.util.Holder)
	 */
	@Override
	public GraphTraversalAction processEdge(N srcNode,
			TarjanSCCRecord srcData, E edge, N tgtNode, Holder dataHolder) {
		TarjanSCCRecord rec = records.get(tgtNode);
		if(rec == null) {
			rec = createRecord();
			dataHolder.value = rec;
			return GraphTraversalAction.EXPLORE;
		}
		
		if(rec.lowLink != NODE_FINISHED) {
			int tgtNum = rec.number;
			if(tgtNum < srcData.lowLink)
				srcData.lowLink = tgtNum;
		}
		return GraphTraversalAction.IGNORE;
	}
	
	/*
	 * (non-Javadoc)
	 * @see net.automatalib.util.graphs.traversal.GraphTraversalVisitor#backtrackEdge(java.lang.Object, java.lang.Object, java.lang.Object, java.lang.Object, java.lang.Object)
	 */
	@Override
	public void backtrackEdge(N srcNode, TarjanSCCRecord srcData, E edge,
			N tgtNode, TarjanSCCRecord tgtData) {
		int tgtLl = tgtData.lowLink;
		if(tgtLl < srcData.lowLink)
			srcData.lowLink = tgtLl;
	}
	
	public boolean hasVisited(N node) {
		return (records.get(node) != null);
	}

	private TarjanSCCRecord createRecord() {
		return new TarjanSCCRecord(counter++);
	}
	
}