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Open-source constraint solver.
There is a newer version: 4.10.17
/*
 * This file is part of choco-solver, http://choco-solver.org/
 *
 * Copyright (c) 2023, IMT Atlantique. All rights reserved.
 *
 * Licensed under the BSD 4-clause license.
 *
 * See LICENSE file in the project root for full license information.
 */
package org.chocosolver.solver.constraints.extension.nary;

import gnu.trove.set.TIntSet;
import gnu.trove.set.hash.TIntHashSet;
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.StoredSparseSet;
import org.chocosolver.util.objects.graphs.MultivaluedDecisionDiagram;

/**
 * Implementation based on "Maintaining GAC on adhoc r-ary constraints", Cheng and Yap, CP12.
 * 
 * Created by cprudhom on 04/11/14.
 * Project: choco.
 */
public class PropLargeMDDC extends Propagator {

    private final TIntSet yes;
    private final TIntSet[] sets;
    private final StoredSparseSet no;
    private final MultivaluedDecisionDiagram MDD;
    private final int nvars;

    /**
     * Create a propagator maintaining GAC based on a MDD.
     * The MDD can be shared between multiple propagators, no copy is achieved.
     *
     * @param MDD  Multi-valued Decision Diagram, stores the solutions
     * @param VARS the related variables -- the order is important, and need to match the MDD.
     */
    public PropLargeMDDC(MultivaluedDecisionDiagram MDD, IntVar... VARS) {
        super(VARS, PropagatorPriority.QUADRATIC, false);
        this.MDD = MDD;
        this.nvars = vars.length;
        this.yes = new TIntHashSet();
        this.no = new StoredSparseSet(VARS[0].getEnvironment());
        this.sets = new TIntHashSet[nvars];
        for (int i = 0; i < nvars; i++) {
            this.sets[i] = new TIntHashSet(vars[i].getDomainSize());
        }
    }

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        mddc();
    }

    @Override
    public ESat isEntailed() {
        if (isCompletelyInstantiated()) {
            int[] diag = MDD.getDiagram();
            int l = 0;
            int n = vars[l].getValue() - MDD.getOffset(l);
            while (l < nvars - 1 && diag[n] > 0) {
                l++;
                n = diag[n] + vars[l].getValue() - MDD.getOffset(l);
            }
            return ESat.eval(l == nvars - 1 && diag[n] == MultivaluedDecisionDiagram.TERMINAL);
        }
        return ESat.UNDEFINED;
    }


    private void mddc() throws ContradictionException {
        yes.clear();
        for (int i = 0; i < nvars; i++) {
            sets[i].clear();
            int o = MDD.getOffset(i);
            int UB = vars[i].getUB();
            for (int j = vars[i].getLB(); j <= UB; j = vars[i].nextValue(j)) {
                sets[i].add(j - o);
            }
        }
        mddcSeekSupport(0, 0);
        for (int i = 0; i < nvars; i++) {
            int o = MDD.getOffset(i);
            int[] values = sets[i].toArray();
            for (int j = 0; j < values.length; j++) {
                vars[i].removeValue(values[j] + o, this);
            }
        }
    }

    private boolean mddcSeekSupport(int node, int layer) {
        // If the node has already been visited
        if (yes.contains(node)) return true;
        if (no.contains(node)) return false;
        // otherwise ...
        boolean res = false;
        // get the initial LB of the variable, required for 'contains'
        int o = MDD.getOffset(layer);
        for (int i = 0; i < MDD.getNodeSize(layer); i++) { // for all node of the same layer
            int sG = MDD.getEdge(node + i); // get the sub-mmd induced
            // if there is a sub-mdds valid
            if (sG != MultivaluedDecisionDiagram.EMPTY && vars[layer].contains(i + o)
                    && (sG == MultivaluedDecisionDiagram.TERMINAL || mddcSeekSupport(sG, layer + 1))) {
                res = true;
                sets[layer].remove(i);
                int l2 = layer;
                while (l2 < nvars && sets[l2].isEmpty()) {
                    l2++;
                }
                if (l2 == nvars) break;
            }
        }
        if (res) {
            yes.add(node);
        } else {
            no.add(node);
        }
        return res;
    }
}