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/*
* 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.nary.clauses;
import gnu.trove.map.hash.TIntObjectHashMap;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.learn.XParameters;
import org.chocosolver.solver.variables.BoolVar;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.view.bool.BoolNotView;
import org.chocosolver.solver.variables.view.bool.BoolEqView;
import org.chocosolver.solver.variables.view.bool.BoolLeqView;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableSetUtils;
import org.chocosolver.util.tools.VariableUtils;
import java.util.*;
/**
* A signed clause builder
*
* Project: choco-solver.
*
* @author Charles Prud'homme
* @since 12/10/2016.
*/
public class ClauseBuilder {
/**
* When the nogood is true (based on variables declared domain)
*/
private static final short ALWAYSTRUE = 0b10;
/**
* * When the nogood is unknown
*/
private static final short UNKNOWN = 0b01;
/**
* When the nogood is false (based on variables declared domain)
*/
private static final short FALSE = 0b00;
/**
* Sets of variables
*/
private final Set vars;
/**
* Sets of forbidden values
*/
private final TIntObjectHashMap sets;
/**
* Status of the nogood to build
*/
private short status = FALSE;
/**
* Initial state of the variables
*/
private final TIntObjectHashMap initialDomains;
/**
* Nogood builder, to ease declaration of nogoods
*
* @param mModel model to declare the nogoods in
*/
public ClauseBuilder(Model mModel) {
vars = new HashSet<>();
sets = new TIntObjectHashMap<>();
initialDomains = new TIntObjectHashMap<>();
Arrays.stream(mModel.retrieveIntVars(true))
.forEach(v -> initialDomains.put(v.getId(), new IntIterableRangeSet(v)));
}
/**
* Add a literal (var ∈ set) in this, considering that the entry is only added once (no
* need to perform internal operations).
* The set can be recycle only after the call to {@link #buildNogood(Model)}
*
* @param var a variable
* @param set a set of values
* @return the nogood maker
*/
public ClauseBuilder put(IntVar var, IntIterableRangeSet set) {
status |= UNKNOWN;
if (var.isAConstant()) {
if (!set.contains(var.getValue())) { //always true and ignore
status |= ALWAYSTRUE;
} // else, always false and ignore
return this;
}
if (set.intersect(initialDomains.get(var.getId()))) {
if (IntIterableSetUtils.includedIn(initialDomains.get(var.getId()), set)) {
status |= ALWAYSTRUE;
}
this.vars.add(var);
this.sets.put(var.getId(), set);
}
return this;
}
/**
* Build the nogood in memory and post it to model.
*/
public void buildNogood(Model model) {
if ((status & ALWAYSTRUE) == 0) {
if ((status & UNKNOWN) != 0) { // at least one clause is unknown
if (XParameters.ELIMINATE_VIEWS) eliminateViews();
vars.removeIf(var -> (sets.get(var.getId()).isEmpty()));
IntVar[] _vars = vars.toArray(new IntVar[0]);
Arrays.sort(_vars); // to avoid undeterministic behavior
switch (vars.size()) {
case 0:
model.falseConstraint().post();
if (XParameters.PRINT_CLAUSE) model.getSolver().log().white().printf("learn: FALSE\n");
break;
case 1:
model.member(_vars[0], sets.get(_vars[0].getId())).post();
if (XParameters.PRINT_CLAUSE) model.getSolver().log().white().printf("learn: %s \u2208 %s\n",
_vars[0], sets.get(_vars[0].getId()));
break;
default:
IntIterableRangeSet[] ranges = new IntIterableRangeSet[_vars.length];
for (int i = 0; i < _vars.length; i++) {
ranges[i] = sets.get(_vars[i].getId());
}
model.getClauseConstraint().addClause(_vars, ranges);
break;
}
} else {
// always false
model.falseConstraint().post();
throw new UnsupportedOperationException();
}
}// else post nothing
this.status = FALSE;
this.vars.clear();
this.sets.clear();
}
private void eliminateViews() {
Stack keys = vars
.stream()
.filter(VariableUtils::isView)
.collect(
Stack::new,
Stack::push,
Vector::addAll
);
while (!keys.isEmpty()) {
IntVar v = keys.pop();
if (v instanceof BoolEqView) {
eliminateEqView((BoolEqView) v, keys);
} else if (v instanceof BoolLeqView) {
eliminateLeqView((BoolLeqView) v, keys);
} else if (v instanceof BoolNotView) {
eliminateNotView((BoolNotView) v, keys);
}
}
}
private void eliminateEqView(BoolEqView ev, Stack keys) {
IntIterableRangeSet set = sets.get(ev.getId());
assert set.size() == 1;
assert set.min()>=0 && set.max() <=1;
IntVar vv = ev.getVariable();
if (set.min() == 1) {
if (vars.contains(vv)) {
sets.get(vv.getId()).add(ev.cste);
} else {
put(vv, new IntIterableRangeSet(ev.cste));
if (VariableUtils.isView(vv)) {
keys.push(vv);
}
}
} else if (set.min() == 0) {
IntIterableRangeSet es = initialDomains.get(vv.getId()).duplicate();
es.remove(ev.cste);
if (vars.contains(vv)) {
sets.get(vv.getId()).addAll(es);
} else {
put(vv, es);
if (VariableUtils.isView(vv)) {
keys.push(vv);
}
}
}
set.clear();
}
private void eliminateLeqView(BoolLeqView lv, Stack keys) {
IntIterableRangeSet set = sets.get(lv.getId());
assert set.size() == 1;
assert set.min()>=0 && set.max() <=1;
IntVar vv = lv.getVariable();
IntIterableRangeSet root = initialDomains.get(vv.getId()).duplicate();
if (set.min() == 1) {
root.retainBetween(IntIterableRangeSet.MIN, lv.cste);
} else if (set.min() == 0) {
root.removeBetween(IntIterableRangeSet.MIN, lv.cste);
}
if (vars.contains(vv)) {
sets.get(vv.getId()).addAll(root);
} else {
put(vv, root);
if (VariableUtils.isView(vv)) {
keys.push(vv);
}
}
set.clear();
}
private void eliminateNotView(BoolNotView nv, Stack keys) {
IntIterableRangeSet set = sets.get(nv.getId());
BoolVar vv = nv.not();
assert set.size() == 1;
int value = set.min();
if (vars.contains(vv)) {
sets.get(vv.getId()).add(1 - value);
} else {
put(vv, new IntIterableRangeSet(1 - value));
if (VariableUtils.isView(vv)) {
keys.push(vv);
}
}
set.clear();
}
public IntIterableRangeSet getInitialDomain(IntVar var) {
return initialDomains.get(var.getId());
}
}