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A graph module for Choco Solver.
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/*
 * Copyright (c) 1999-2014, Ecole des Mines de Nantes
 * All rights reserved.
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Ecole des Mines de Nantes nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.chocosolver.graphsolver.cstrs.connectivity;

import org.chocosolver.graphsolver.util.ConnectivityFinder;
import org.chocosolver.graphsolver.variables.GraphEventType;
import org.chocosolver.graphsolver.variables.UndirectedGraphVar;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.setDataStructures.ISet;
import org.chocosolver.util.objects.setDataStructures.ISetIterator;

import java.util.BitSet;

/**
 * Propagator checking that the graph is connected
 * can filter by forcing bridges
 *
 * In case not all vertices are mandatory, the filtering could be improved
 *
 * @author Jean-Guillaume Fages
 */
public class PropConnected extends Propagator {


	//***********************************************************************************
	// VARIABLES
	//***********************************************************************************

	private int n;
	private BitSet visited;
	private int[] fifo;
	private UndirectedGraphVar g;
	private ConnectivityFinder env_CC_finder;
	private boolean checkerOnly;

	//***********************************************************************************
	// CONSTRUCTORS
	//***********************************************************************************

	public PropConnected(UndirectedGraphVar graph) {
		this(graph,false);
	}

	public PropConnected(UndirectedGraphVar graph, boolean checkerOnly) {
		super(new UndirectedGraphVar[]{graph}, PropagatorPriority.LINEAR, false);
		this.g = graph;
		this.n = graph.getNbMaxNodes();
		this.visited = new BitSet(n);
		this.fifo = new int[n];
		this.env_CC_finder = new ConnectivityFinder(g.getUB());
		this.checkerOnly = checkerOnly;
	}

	//***********************************************************************************
	// METHODS
	//***********************************************************************************

	@Override
	public int getPropagationConditions(int vIdx) {
		return GraphEventType.REMOVE_ARC.getMask() + GraphEventType.ADD_NODE.getMask() + GraphEventType.REMOVE_NODE.getMask();
	}

	@Override
	public void propagate(int evtmask) throws ContradictionException {
		if (g.getPotentialNodes().size() == 0) {
			fails();
		}
		if(g.getMandatoryNodes().size()>1) {
			// explore the graph from the first mandatory node
			explore();
			// remove unreachable nodes
			for (int o = visited.nextClearBit(0); o < n; o = visited.nextClearBit(o + 1)) {
				g.removeNode(o,this);
			}
			// force articulation points
			if(g.getLB().getNodes().size()= numOfNode[i] && i != start) {
					if (mandInSub[i] && !mandNodes.contains(i)) // must contain a mandatory node in subtree
						g.enforceNode(i, this); // ARTICULATION POINT DETECTED
				}
			}
		}
	}
}