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Open-source constraint solver.
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2020, 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.lex;
import org.chocosolver.memory.IEnvironment;
import org.chocosolver.memory.IStateInt;
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.solver.variables.events.PropagatorEventType;
import org.chocosolver.util.ESat;
import org.chocosolver.util.tools.ArrayUtils;
import java.util.Arrays;
/**
* Enforce a lexicographic ordering on two vectors of integer
* variables x <_lex y with x = , and y = .
* ref : Global Constraints for Lexicographic Orderings (Frisch and al)
*
*
* @author Charles Prud'homme
* @since 10/08/11
*/
public class PropLex extends Propagator {
private final int n; // size of both vectors
private final IStateInt alpha; // size of both vectors
private final IStateInt beta;
private boolean entailed;
private final IntVar[] x;
private final IntVar[] y;
private final boolean strict;
public PropLex(IntVar[] X, IntVar[] Y, boolean strict) {
super(ArrayUtils.append(X, Y), PropagatorPriority.LINEAR, true);
this.x = Arrays.copyOfRange(vars, 0, X.length);
this.y = Arrays.copyOfRange(vars, X.length, vars.length);
this.strict = strict;
this.n = X.length;
IEnvironment environment = model.getEnvironment();
alpha = environment.makeInt(0);
beta = environment.makeInt(0);
entailed = false;
}
@Override
public void propagate(int evtmask) throws ContradictionException {
if (PropagatorEventType.isFullPropagation(evtmask)) {
initialize();
} else {
gacLexLeq(alpha.get());
}
}
@Override
public void propagate(int vIdx, int mask) throws ContradictionException {
entailed = false;
if (vIdx < n) {
gacLexLeq(vIdx);
} else {
gacLexLeq(vIdx - n);
}
}
@Override
public ESat isEntailed() {
if (isCompletelyInstantiated()) {
for (int i = 0; i < x.length; i++) {
int xi = vars[i].getValue();
int yi = vars[i + n].getValue();
if (xi < yi) {
return ESat.TRUE;
} else if (xi > yi) {
return ESat.FALSE;
}//else xi == yi
}
if (strict) {
return ESat.FALSE;
} else {
return ESat.TRUE;
}
}
return ESat.UNDEFINED;
}
/////////////////////
private boolean groundEq(IntVar x1, IntVar y1) {
return x1.isInstantiated() && y1.isInstantiated() && x1.getValue() == y1.getValue();
}
private boolean checkLex(int i) {
if (!strict) {
if (i == n - 1) {
return x[i].getUB() <= y[i].getLB();
} else {
return x[i].getUB() < y[i].getLB();
}
} else {
return x[i].getUB() < y[i].getLB();
}
}
private void updateAlpha(int i) throws ContradictionException {
if (i == beta.get()) {
fails();
}
if (i == n) {
if (strict) {
fails();
} else {
entailed = true;
setPassive();
return;
}
}
if (!groundEq(x[i], y[i])) {
alpha.set(i);
gacLexLeq(i);
} else {
updateAlpha(i + 1);
}
}
private void updateBeta(int i) throws ContradictionException {
if ((i + 1) == alpha.get()) {
fails();
}
if (x[i].getLB() < y[i].getUB()) {
beta.set(i + 1);
if (x[i].getUB() >= y[i].getLB()) {
gacLexLeq(i);
}
} else if (x[i].getLB() == y[i].getUB()) {
updateBeta(i - 1);
}
}
/**
* Build internal structure of the propagator, if necessary
*
* @throws org.chocosolver.solver.exception.ContradictionException if initialisation encounters a contradiction
*/
private void initialize() throws ContradictionException {
entailed = false;
int i = 0;
int a, b;
while (i < n && groundEq(x[i], y[i])) {
i++;
}
if (i == n) {
if (!strict) {
entailed = true;
setPassive();
} else {
fails();
}
} else {
a = i;
if (checkLex(i)) {
setPassive();
return;
}
b = -1;
while (i != n && x[i].getLB() <= y[i].getUB()) {
if (x[i].getLB() == y[i].getUB()) {
if (b == -1) {
b = i;
}
} else {
b = -1;
}
i++;
}
if (!strict && i == n) {
b = Integer.MAX_VALUE;
}
if (b == -1) {
b = i;
}
if (a >= b) {
fails();
}
alpha.set(a);
beta.set(b);
gacLexLeq(a);
}
}
private void gacLexLeq(int i) throws ContradictionException {
int a = alpha.get();
int b = beta.get();
//Part A
if (i >= b || entailed) {
return;
}
//Part B
if (i == a && (i + 1) == b) {
x[i].updateUpperBound(y[i].getUB() - 1, this);
y[i].updateLowerBound(x[i].getLB() + 1, this);
if (checkLex(i)) {
entailed = true;
setPassive();
return;
}
}
//Part C
if (i == a && (i + 1) < b) {
x[i].updateUpperBound(y[i].getUB(), this);
y[i].updateLowerBound(x[i].getLB(), this);
if (checkLex(i)) {
entailed = true;
setPassive();
return;
}
if (groundEq(x[i], y[i])) {
updateAlpha(i + 1);
}
}
//Part D
if (a < i /*&& i < b*/) {
if ((i == (b - 1) && x[i].getLB() == y[i].getUB()) || x[i].getLB() > y[i].getUB()) {
updateBeta(i - 1);
}
}
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder(32);
sb.append("LEX <");
int i = 0;
for (; i < Math.min(this.x.length - 1, 2); i++) {
sb.append(this.x[i]).append(", ");
}
if (i == 2 && this.x.length - 1 > 2) sb.append("..., ");
sb.append(this.x[x.length - 1]);
sb.append(">, <");
i = 0;
for (; i < Math.min(this.y.length - 1, 2); i++) {
sb.append(this.y[i]).append(", ");
}
if (i == 2 && this.y.length - 1 > 2) sb.append("..., ");
sb.append(this.y[y.length - 1]);
sb.append(">");
return sb.toString();
}
}