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A graph module for Choco Solver.
There is a newer version: 4.2.2
/*
 * 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.cost.trees;

import org.chocosolver.graphsolver.variables.GraphEventType;
import org.chocosolver.graphsolver.variables.IUndirectedGraphVar;
import org.chocosolver.graphsolver.variables.delta.IGraphDeltaMonitor;
import org.chocosolver.memory.IEnvironment;
import org.chocosolver.memory.IStateInt;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.setDataStructures.ISet;
import org.chocosolver.util.procedure.PairProcedure;

/**
 * Compute the cost of the graph by summing edge costs
 * - For minimization problem
 */
public class PropTreeCostSimple extends Propagator {

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

    protected IUndirectedGraphVar g;
    private IGraphDeltaMonitor gdm;
    private PairProcedure edgeEnf, edgeRem;
    protected int n;
    protected IntVar sum;
    protected int[][] distMatrix;
    private IStateInt minSum, maxSum;

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

    public PropTreeCostSimple(IUndirectedGraphVar graph, IntVar obj, int[][] costMatrix) {
        super(new IUndirectedGraphVar[]{graph}, PropagatorPriority.LINEAR, true);
        g = graph;
        sum = obj;
        n = g.getNbMaxNodes();
        distMatrix = costMatrix;
		IEnvironment environment = graph.getEnvironment();
        minSum = environment.makeInt(0);
        maxSum = environment.makeInt(0);
        gdm = g.monitorDelta(this);
        edgeEnf = (i, j) -> minSum.add(distMatrix[i][j]);
        edgeRem = (i, j) -> maxSum.add(-distMatrix[i][j]);
    }

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

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        int min = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            ISet nei = g.getPotNeighOf(i);
            for (int j : nei) {
                if (i <= j) {
                    max += distMatrix[i][j];
                    if (g.getMandNeighOf(i).contains(j)) {
                        min += distMatrix[i][j];
                    }
                }
            }
        }
		gdm.unfreeze();
        minSum.set(min);
        maxSum.set(max);
        sum.updateLowerBound(min, this);
        sum.updateUpperBound(max, this);
    }

    @Override
    public void propagate(int idxVarInProp, int mask) throws ContradictionException {
		gdm.freeze();
		gdm.forEachArc(edgeEnf, GraphEventType.ADD_ARC);
		gdm.forEachArc(edgeRem, GraphEventType.REMOVE_ARC);
		gdm.unfreeze();
        sum.updateLowerBound(minSum.get(), this);
        sum.updateUpperBound(maxSum.get(), this);
    }

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

    @Override
    public ESat isEntailed() {
        int min = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            ISet nei = g.getPotNeighOf(i);
            for (int j : nei) {
                if (i <= j) {
                    max += distMatrix[i][j];
                    if (g.getMandNeighOf(i).contains(j)) {
                        min += distMatrix[i][j];
                    }
                }
            }
        }
        if (min > sum.getUB() || max < sum.getLB()) {
            return ESat.FALSE;
        }
        if (min == max) {
            return ESat.TRUE;
        } else {
            return ESat.UNDEFINED;
        }
    }
}