Package solver.constraints.binary

Source Code of solver.constraints.binary.PropNotEqualX_YC

/*
* 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:
*
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*       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
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*       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
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package solver.constraints.binary;

import gnu.trove.map.hash.THashMap;
import solver.Solver;
import solver.constraints.Propagator;
import solver.constraints.PropagatorPriority;
import solver.exception.ContradictionException;
import solver.explanations.Deduction;
import solver.explanations.Explanation;
import solver.explanations.VariableState;
import solver.variables.IntVar;
import solver.variables.Variable;
import solver.variables.events.IntEventType;
import util.ESat;

/**
* A specific <code>Propagator</code> extension defining filtering algorithm for:
* <br/>
* <b>X =/= Y + C</b>
* <br>where <i>X</i> and <i>Y</i> are <code>Variable</code> objects and <i>C</i> a constant.
* <br>
* This <code>Propagator</code> defines the <code>propagate</code> and <code>awakeOnInst</code> methods. The other ones
* throw <code>UnsupportedOperationException</code>.
* <br/>
* <br/>
* <i>Based on Choco-2.1.1</i>
*
* @author Xavier Lorca
* @author Charles Prud'homme
* @author Arnaud Malapert
* @version 0.01, june 2010
* @since 0.01
*/
public class PropNotEqualX_YC extends Propagator<IntVar> {

    IntVar x;
    IntVar y;
    int cste;

    @SuppressWarnings({"unchecked"})
    public PropNotEqualX_YC(IntVar[] vars, int c) {
        super(vars, PropagatorPriority.BINARY, true);
        this.x = vars[0];
        this.y = vars[1];
        this.cste = c;
    }

    @Override
    public int getPropagationConditions(int vIdx) {
        //Principle : if v0 is instantiated and v1 is enumerated, then awakeOnInst(0) performs all needed pruning
        //Otherwise, we must check if we can remove the value from v1 when the bounds has changed.
        if (vars[vIdx].hasEnumeratedDomain()) {
            return IntEventType.instantiation();
        }
        return IntEventType.boundAndInst();
    }

    @Override
    public void propagate(int evtmask) throws ContradictionException {
        if (x.isInstantiated()) {
            removeValV1();
        } else if (y.isInstantiated()) {
            removeValV0();
        } else if (x.getUB() < (y.getLB() + cste) || (y.getUB() + cste) < x.getLB()) {
            setPassive();
        }
    }

    @Override
    public void propagate(int varIdx, int mask) throws ContradictionException {
        // typical case: A=[1,4], B=[1,4] (bounded domains)
        // A instantiated to 3 => nothing can be done on B
        // then B dec supp to 3 => 3 can also be removed du to A = 3.
        propagate(0);
    }

    private void removeValV0() throws ContradictionException {
        if (x.removeValue(y.getValue() + this.cste, aCause)
                || !x.contains(y.getValue() + cste)) {
            this.setPassive();
        }
    }

    private void removeValV1() throws ContradictionException {
        if (y.removeValue(x.getValue() - this.cste, aCause)
                || !y.contains(x.getValue() - cste)) {
            this.setPassive();
        }
    }

    @Override
    public ESat isEntailed() {
        if ((x.getUB() < y.getLB() + this.cste) ||
                (y.getUB() < x.getLB() - this.cste))
            return ESat.TRUE;
        else if (x.isInstantiated()
                && y.isInstantiated()
                && x.getValue() == y.getValue() + this.cste)
            return ESat.FALSE;
        else
            return ESat.UNDEFINED;
    }

    @Override
    public String toString() {
        StringBuilder bf = new StringBuilder();
        bf.append("prop(").append(vars[0].getName()).append(".NEQ.").append(vars[1].getName());
        bf.append("+").append(cste).append(")");
        return bf.toString();
    }

    @Override
    public void explain(Deduction d, Explanation e) {
        e.add(solver.getExplainer().getPropagatorActivation(this));
        Variable var = d.getVar();
        if (var.equals(x)) {
            // a deduction has been made on x ; this is related to y only
            y.explain(VariableState.DOM, e);
        } else if (var != null) {
            x.explain(VariableState.DOM, e);
        }
        // and the application of the current propagator
        e.add(aCause);
    }

    @Override
    public void duplicate(Solver solver, THashMap<Object, Object> identitymap) {
        if (!identitymap.containsKey(this)) {
            this.vars[0].duplicate(solver, identitymap);
            IntVar X = (IntVar) identitymap.get(this.vars[0]);
            this.vars[1].duplicate(solver, identitymap);
            IntVar Y = (IntVar) identitymap.get(this.vars[1]);

            identitymap.put(this, new PropNotEqualX_YC(new IntVar[]{X, Y}, this.cste));
        }
    }
}
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