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Open-source constraint solver.
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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.nary.nvalue;
import gnu.trove.list.array.TIntArrayList;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.util.ESat;
import java.util.BitSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import static org.chocosolver.solver.constraints.PropagatorPriority.QUADRATIC;
import static org.chocosolver.util.tools.ArrayUtils.concat;
/**
* Propagator for the atMostNValues constraint
* The number of distinct values in the set of variables vars is at most equal to nValues
* No level of consistency but better than BC in general (for enumerated domains with holes)
*
* @author Jean-Guillaume Fages
*/
public class PropAtMostNValues extends Propagator {
//***********************************************************************************
// VARIABLES
//***********************************************************************************
private final int[] concernedValues;
private final int n;
private final int[] unusedValues;
private final int[] mate;
private boolean allEnum; // all variables are enumerated
private final int[] instVals; // for K1
private final TIntArrayList dVar;
private int minVal, nbInst;
private final BitSet valSet;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
/**
* Propagator for the NValues constraint
* The number of distinct values among concerned values in the set of variables vars is exactly equal to nValues
* No level of consistency for the filtering
*
* @param variables array of variables
* @param concernedValues will be sorted!
* @param nValues integer variable
*/
public PropAtMostNValues(IntVar[] variables, int[] concernedValues, IntVar nValues) {
super(concat(variables, nValues), QUADRATIC, false);
n = variables.length;
this.concernedValues = concernedValues;
unusedValues = new int[concernedValues.length];
mate = new int[concernedValues.length];
allEnum = true;
minVal = Integer.MAX_VALUE / 10;
int maxVal = -minVal;
for (int i = 0; i < n; i++) {
allEnum &= vars[i].hasEnumeratedDomain();
minVal = Math.min(minVal, vars[i].getLB());
maxVal = Math.max(maxVal, vars[i].getUB());
}
valSet = new BitSet(maxVal - minVal + 1);
instVals = new int[n];
dVar = new TIntArrayList();
}
//***********************************************************************************
// PROPAGATION
//***********************************************************************************
@Override
public void propagate(int evtmask) throws ContradictionException {
vars[n].updateLowerBound(1, this);
int count = 0;
int countMax = 0;
int idx = 0;
nbInst = 0;
for (int i = concernedValues.length - 1; i >= 0; i--) {
boolean possible = false;
boolean mandatory = false;
mate[i] = -1;
int value = concernedValues[i];
for (int v = 0; v < n; v++) {
if (vars[v].contains(value)) {
possible = true;
if (mate[i] == -1) {
mate[i] = v;
} else {
mate[i] = -2;
if (mandatory) {
break;
}
}
if (vars[v].isInstantiated()) {
mandatory = true;
if (mate[i] == -2) {
break;
}
}
}
}
if (possible) {
countMax++;
}
if (mandatory) {
instVals[count] = value;
count++;
} else {
unusedValues[idx++] = value;
}
}
nbInst = count;
// filtering cardinality variable
vars[n].updateLowerBound(count, this);
// filtering decision variables
if (count != countMax && vars[n].isInstantiated())
if (count == vars[n].getUB()) {
int val;
for (int i = 0; i < idx; i++) {
val = unusedValues[i];
for (int v = 0; v < n; v++) {
vars[v].removeValue(val, this);
}
}
for (int i = idx - 1; i >= 0; i--) {
val = unusedValues[i];
for (int v = 0; v < n; v++) {
vars[v].removeValue(val, this);
}
}
if (allEnum) setPassive();
} else if (count == vars[n].getUB() - 1) {
filterK1Rule();
}
}
//***********************************************************************************
// K1 (from Hadrien Cambazard)
//***********************************************************************************
private void filterK1Rule() throws ContradictionException {
dVar.clear();
for (int i = 0; i < n; i++) {
if (!vars[i].isInstantiated()) {
if (emptyIntersectionWith(vars[i], instVals)) {
dVar.add(i);
}
}
}
if (!dVar.isEmpty()) {
intersectionDomains();
for (int i = 0; i < nbInst; i++) {
valSet.set(instVals[i] - minVal);
}
for (int i = 0; i < n; i++) {
if (!vars[i].isInstantiated()) {
restrict(vars[i]);
}
}
}
}
private boolean emptyIntersectionWith(final IntVar v, int[] valueSet) {
for (int val : valueSet) {
if (v.contains(val)) {
return false;
}
}
return true;
}
private void intersectionDomains() {
final List inter = new LinkedList<>();
IntVar v = vars[dVar.get(0)];
for (int val = v.getLB(); val <= v.getUB(); val = v.nextValue(val)) {
inter.add(val);
}
for (int i = 0; i < dVar.size(); i++) {
final int next = dVar.get(i);
v = vars[next];
for (final Iterator it = inter.iterator(); it.hasNext(); ) {
if (!v.contains((Integer) it.next())) {
it.remove();
}
}
}
valSet.clear();
for (final Integer i : inter) {
valSet.set(i - minVal);
}
}
private void restrict(final IntVar v) throws ContradictionException {
if (v.hasEnumeratedDomain()) {
for (int val = v.getLB(); val <= v.getUB(); val = v.nextValue(val)) {
if (!valSet.get(val - minVal)) {
v.removeValue(val, this);
}
}
} else {
int lb = v.getLB();
int ub = v.getLB();
for (int val = v.getLB(); val <= ub; val = v.nextValue(val)) {
if (!valSet.get(val - minVal)) {
lb = val + 1;
} else {
break;
}
}
for (int val = v.getUB(); val >= lb; val = v.previousValue(val)) {
if (!valSet.get(val - minVal)) {
ub = val - 1;
} else {
break;
}
}
v.updateBounds(lb, ub, this);
}
}
//***********************************************************************************
// INFO
//***********************************************************************************
@Override
public ESat isEntailed() {
int countMin = 0;
int countMax = 0;
for (int i = 0; i < concernedValues.length; i++) {
boolean possible = false;
boolean mandatory = false;
for (int v = 0; v < n; v++) {
if (vars[v].contains(concernedValues[i])) {
possible = true;
if (vars[v].isInstantiated()) {
mandatory = true;
break;
}
}
}
if (possible) {
countMax++;
}
if (mandatory) {
countMin++;
}
}
if (countMin > vars[n].getUB()) {
return ESat.FALSE;
}
if (countMax <= vars[n].getLB()) {
return ESat.TRUE;
}
return ESat.UNDEFINED;
}
}