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/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2024, 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.graph.basic;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.constraints.nary.nvalue.amnv.mis.F;
import org.chocosolver.solver.constraints.nary.nvalue.amnv.mis.MDRk;
import org.chocosolver.solver.constraints.nary.nvalue.amnv.rules.R;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.UndirectedGraphVar;
import org.chocosolver.solver.variables.Variable;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.graphs.UndirectedGraph;
import org.chocosolver.util.objects.setDataStructures.ISet;
import org.chocosolver.util.objects.setDataStructures.SetType;
import java.util.BitSet;
/**
* Propagator for the number of cliques in a graph
*
* @author Jean-Guillaume Fages
*/
public class PropNbCliques extends Propagator {
//***********************************************************************************
// VARIABLES
//***********************************************************************************
private final UndirectedGraphVar g;
private final UndirectedGraph support;
private final IntVar[] nb;
private final R[] rules;
private final F heur;
private int delta;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
public PropNbCliques(UndirectedGraphVar g, IntVar nb) {
super(new Variable[]{g, nb}, PropagatorPriority.QUADRATIC, false);
this.g = g;
this.support = new UndirectedGraph(g.getNbMaxNodes(), SetType.BITSET, false);
this.nb = new IntVar[]{nb};
this.rules = new R[]{new Rcustom()};
this.heur = new MDRk(support, 30);
}
//***********************************************************************************
// METHODS
//***********************************************************************************
@Override
public void propagate(int evtmask) throws ContradictionException {
// reset
int n = g.getNbMaxNodes();
support.getNodes().clear();
for (int i = 0; i < n; i++) {
support.getNeighborsOf(i).clear();
}
ISet nodes = g.getMandatoryNodes();
for (int i : nodes) {
support.addNode(i);
}
for (int i : nodes) {
ISet nei = g.getPotentialNeighborsOf(i);
for (int j : nei) {
if (i < j) {
support.addEdge(i, j);
}
}
}
delta = n - g.getMandatoryNodes().size();
// algorithm
heur.prepare();
do {
heur.computeMIS();
for (R rule : rules) {
rule.filter(nb, support, heur, this);
}
} while (heur.hasNextMIS());
}
@Override
public ESat isEntailed() {
return ESat.TRUE; // redundant propagator (in addition to transitivity and nbConnectedComponents
}
class Rcustom implements R {
@Override
public void filter(IntVar[] nbCliques, UndirectedGraph graph, F heur, Propagator aCause) throws ContradictionException {
assert nbCliques.length == 1;
int n = graph.getNbMaxNodes();
BitSet mis = heur.getMIS();
int LB = heur.getMIS().cardinality() - delta;
nbCliques[0].updateLowerBound(LB, aCause);
if (LB == nbCliques[0].getUB()) {
ISet nei;
for (int i = mis.nextClearBit(0); i >= 0 && i < n; i = mis.nextClearBit(i + 1)) {
int mate = -1;
nei = graph.getNeighborsOf(i);
for (int j : nei) {
if (mis.get(j)) {
if (mate == -1) {
mate = j;
} else if (mate >= 0) {
mate = -2;
break;
}
}
}
if (mate >= 0) {
g.enforceEdge(i, mate, aCause);
}
}
}
}
}
}