org.chocosolver.solver.constraints.nary.alldifferentprec.PropAllDiffPrec Maven / Gradle / Ivy
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2022, IMT Atlantique. All rights reserved.
*
* Licensed under the BSD 4-clause license.
*
* See LICENSE file in the project root for full license information.
*/
/*
@author Arthur Godet
@since 01/02/2021
*/
package org.chocosolver.solver.constraints.nary.alldifferentprec;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.nary.alldifferent.algo.AlgoAllDiffBC;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.graphs.DirectedGraph;
import org.chocosolver.util.objects.setDataStructures.ISetIterator;
import org.chocosolver.util.objects.setDataStructures.SetType;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.stream.IntStream;
/**
* Propagator for the AllDiffPrec constraint.
*
* @author Arthur Godet
*/
public class PropAllDiffPrec extends Propagator {
private final IntVar[] variables;
private final boolean[][] precedence;
private final FilterAllDiffPrec filter;
private final AlgoAllDiffBC allDiffBC;
private final DirectedGraph precGraph;
private final int[] topologicalTraversal;
/**
* Builds a propagator for the AllDiffPrec constraint. The predecessors and successors matrix are built as following:
* with n = |variables|, for all i in [0,n-1], if there is k such that predecessors[i][k] = j then variables[j] is a predecessor of variables[i].
* Similarly, with n = |variables|, for all i in [0,n-1], if there is k such that successors[i][k] = j then variables[j] is a successor of variables[i].
* The matrix should be built such that, if variables[i] is a predecessor of variables[j], then i is in successors[j] and vice versa.
*
* filter should be one of the following (depending on the wanted filtering algorithm): BESSIERE, GREEDY, GREEDY_RC, GODET_RC, GODET_BC or DEFAULT (which is GODET_BC).
*
* @param variables the variables
* @param predecessors the predecessors matrix
* @param successors the successors matrix
* @param filter the name of the filtering scheme
*/
public PropAllDiffPrec(IntVar[] variables, int[][] predecessors, int[][] successors, String filter) {
this(variables, buildPrecedence(predecessors, successors), filter);
}
/**
* Builds a propagator for the AllDiffPrec constraint. The precedence matrix is built as following:
* with n = |variables|, for all i,j in [0,n-1], precedence[i][j] = true iff precedence[j][i] = false iff variables[i] precedes variables[j].
*
* filter should be one of the following (depending on the wanted filtering algorithm): BESSIERE, GREEDY, GREEDY_RC, GODET_RC, GODET_BC or DEFAULT (which is GODET_BC).
*
* @param variables the variables
* @param precedence the precedence matrix
* @param filter the name of the filtering scheme
*/
public PropAllDiffPrec(IntVar[] variables, boolean[][] precedence, String filter) {
this(variables, precedence, buildFilter(variables, precedence, filter));
}
/**
* Builds a propagator for the AllDiffPrec constraint. The precedence matrix is built as following:
* with n = |variables|, for all i,j in [0,n-1], precedence[i][j] = true iff precedence[j][i] = false iff variables[i] precedes variables[j].
*
* @param variables the variables
* @param precedence the precedence matrix
* @param filter the filtering scheme
*/
public PropAllDiffPrec(IntVar[] variables, boolean[][] precedence, FilterAllDiffPrec filter) {
super(variables, filter.getPriority(), false);
this.variables = variables;
this.precedence = precedence;
this.filter = filter;
if(filter instanceof AllDiffPrec) {
allDiffBC = new AlgoAllDiffBC(this);
allDiffBC.reset(vars);
} else {
allDiffBC = null;
}
precGraph = buildPrecGraph(precedence);
topologicalTraversal = buildTopologicalTraversal(precGraph);
}
@Override
public int getPropagationConditions(int vIdx) {
return filter.getPropagationConditions(vIdx);
}
private boolean updateBound(boolean lb) throws ContradictionException {
boolean hasFiltered = false;
ISetIterator iterator;
for(int k = 0; k < topologicalTraversal.length; k++) {
int var = lb ? topologicalTraversal[k] : topologicalTraversal[topologicalTraversal.length-1-k];
iterator = lb ? precGraph.getSuccessorsOf(var).iterator() : precGraph.getPredecessorsOf(var).iterator();
while(iterator.hasNext()) {
int rel = iterator.nextInt();
if(lb) { // rel is a successor of var
if(variables[rel].updateLowerBound(variables[var].getLB() + 1, this)) {
hasFiltered = true;
}
} else { // rel is a predecessor of var
if(variables[rel].updateUpperBound(variables[var].getUB() - 1, this)) {
hasFiltered = true;
}
}
}
}
return hasFiltered;
}
private void filterPrecedenceAndBounds() throws ContradictionException {
boolean hasFiltered;
do {
hasFiltered = updateBound(true);
hasFiltered |= updateBound(false);
if(allDiffBC != null) {
hasFiltered |= allDiffBC.filter();
}
} while(hasFiltered);
}
@Override
public void propagate(int evtmask) throws ContradictionException {
boolean hasFiltered;
do {
filterPrecedenceAndBounds(); // idempotent, no need to register hasFiltered
hasFiltered = filter.propagate(precGraph, topologicalTraversal, this);
} while(hasFiltered);
}
@Override
public ESat isEntailed() {
if(isCompletelyInstantiated()) {
for(int i = 0; i < variables.length; i++) {
for(int j = i + 1; j < variables.length; j++) {
if(
variables[i].getValue() == variables[j].getValue()
|| precedence[i][j] && variables[i].getValue() > variables[j].getValue()
|| precedence[j][i] && variables[i].getValue() < variables[j].getValue()
) {
return ESat.FALSE;
}
}
}
return ESat.TRUE;
}
return ESat.UNDEFINED;
}
//***********************************************************************************
// Build data
//***********************************************************************************
/**
* Builds the ancestors matrix.
*
* @param predecessors the predecessors matrix
* @param successors the successors matrix
* @return the ancestors matrix
*/
public static int[][] buildAncestors(int[][] predecessors, int[][] successors) {
int n = predecessors.length;
int[][] ancestors = new int[n][];
HashSet[] sets = new HashSet[n];
LinkedList list = new LinkedList<>();
boolean[] done = new boolean[n];
for(int i = 0; i < n; i++) {
sets[i] = new HashSet<>(n);
if(predecessors[i].length == 0) {
list.addLast(i);
}
}
while(!list.isEmpty()) {
int i = list.removeFirst();
if(!done[i]) {
boolean allDone = true;
for(int j = 0; j < predecessors[i].length && allDone; j++) {
allDone = done[predecessors[i][j]];
}
if(allDone) {
for(int j = 0; j < predecessors[i].length; j++) {
sets[i].add(predecessors[i][j]);
sets[i].addAll(sets[predecessors[i][j]]);
}
for(int j = 0; j < successors[i].length; j++) {
list.addLast(successors[i][j]);
}
done[i] = true;
}
}
}
for(int i = 0; i < n; i++) {
ancestors[i] = new int[sets[i].size()];
Iterator iter = sets[i].iterator();
int j = 0;
while(iter.hasNext()) {
ancestors[i][j++] = iter.next();
}
}
return ancestors;
}
/**
* Builds the descendants matrx.
*
* @param predecessors the predecessors matrix
* @param successors the successors matrix
* @return the descendants matrix
*/
public static int[][] buildDescendants(int[][] predecessors, int[][] successors) {
int n = successors.length;
int[][] descendants = new int[n][];
HashSet[] sets = new HashSet[n];
LinkedList list = new LinkedList<>();
boolean[] done = new boolean[n];
for(int i = 0; i < n; i++) {
sets[i] = new HashSet<>();
if(successors[i].length == 0) {
list.addLast(i);
}
}
while(!list.isEmpty()) {
int i = list.removeFirst();
if(!done[i]) {
boolean allDone = true;
for(int j = 0; j < successors[i].length && allDone; j++) {
allDone = done[successors[i][j]];
}
if(allDone) {
for(int j = 0; j < successors[i].length; j++) {
sets[i].add(successors[i][j]);
sets[i].addAll(sets[successors[i][j]]);
}
for(int j = 0; j < predecessors[i].length; j++) {
list.addLast(predecessors[i][j]);
}
done[i] = true;
}
}
}
for(int i = 0; i < n; i++) {
descendants[i] = new int[sets[i].size()];
Iterator iter = sets[i].iterator();
int j = 0;
while(iter.hasNext()) {
descendants[i][j++] = iter.next();
}
}
return descendants;
}
/**
* Returns true iff the array a contains the value v.
*
* @param a the array
* @param v the value
* @return true iff the array a contains the value v
*/
public static boolean contains(int[] a, int v) {
return contains(a, v, a.length);
}
/**
* Returns true iff the array a contains the value v before the index maxIdx (strictly).
*
* @param a the array
* @param v the value
* @param maxIdx the maximum index
* @return true iff a contains v before index maxIdx
*/
public static boolean contains(int[] a, int v, int maxIdx) {
for(int i = 0; i < maxIdx; i++) {
if(a[i] == v) {
return true;
}
}
return false;
}
public static boolean[][] buildPrecedence(int[][] predecessors, int[][] successors) {
return buildPrecedence(predecessors, successors, false);
}
/**
* Returns the precedence matrix, such that precedence[v][w] = true iff v is a predecessor of w.
*
* @param predecessors the predecessors matrix
* @param successors the successors matrix
* @param alreadyComputed true iff predecessors and successors matrix are ancestors and descendants matrix
* @return the precedence matrix
*/
public static boolean[][] buildPrecedence(int[][] predecessors, int[][] successors, boolean alreadyComputed) {
int[][] ancestors = alreadyComputed ? predecessors : buildAncestors(predecessors, successors);
int[][] descendants = alreadyComputed ? successors : buildDescendants(predecessors, successors);
int n = predecessors.length;
boolean[][] precedence = new boolean[n][n];
for(int i = 0; i < n; i++) {
precedence[i][i] = false;
for(int j = i + 1; j < n; j++) {
if(contains(ancestors[i], j)) {
precedence[j][i] = true;
} else if(contains(descendants[i], j)) {
precedence[i][j] = true;
}
// nothing to do in the else case
}
}
return precedence;
}
public static DirectedGraph buildPrecGraph(boolean[][] precedence) {
int n = precedence.length;
DirectedGraph precGraph = new DirectedGraph(n, SetType.BITSET, true);
for(int v = 0; v < n; v++) {
for(int w = v + 1; w < n; w++) {
if(precedence[v][w]) {
precGraph.addEdge(v, w);
} else if(precedence[w][v]) {
precGraph.addEdge(w, v);
}
}
}
return precGraph;
}
/**
* Builds the topological traversal of the given precedence graph.
*
* @param precGraph the precedence graph
* @return the topological traversal
*/
public static int[] buildTopologicalTraversal(DirectedGraph precGraph) {
int n = precGraph.getNbMaxNodes();
int[] depth = new int[n];
LinkedList queue = new LinkedList<>();
for(int v = 0; v < n; v++) {
if(precGraph.getPredecessorsOf(v).isEmpty()) {
queue.addLast(v);
}
}
while(!queue.isEmpty()) {
int v = queue.removeFirst();
ISetIterator iterator = precGraph.getPredecessorsOf(v).iterator();
while(iterator.hasNext()) {
int pre = iterator.nextInt();
depth[v] = Math.max(depth[v], depth[pre] + 1);
}
iterator = precGraph.getSuccessorsOf(v).iterator();
while(iterator.hasNext()) {
int succ = iterator.nextInt();
if(!queue.contains(succ)) {
queue.addLast(succ);
}
}
}
return IntStream.range(0, n)
.boxed()
.sorted(Comparator.comparingInt(i -> depth[i]))
.mapToInt(i -> i)
.toArray();
}
/**
* Returns the filtering algorithm structure for the given variables, the precedence and whose behaviour is one of the following:
* BESSIERE, GREEDY, GREEDY_RC, GODET_RC, GODET_BC or DEFAULT (which is GODET_BC).
*
* @param variables the variables
* @param precedence the precedence matrix
* @param filt the filtering algorithm to select
* @return the filtering algorithm
*/
public static FilterAllDiffPrec buildFilter(IntVar[] variables, boolean[][] precedence, String filt) {
switch(filt) {
case "BESSIERE": return new AllDiffPrec(variables, precedence);
case "GREEDY": return new GreedyBoundSupport(variables, precedence);
case "GREEDY_RC": return new GreedyBoundSupport(variables, precedence,true);
case "GODET_RC": return new AllDiffPrecMoreThanBc(variables, precedence, true);
case "GODET":
case "DEFAULT":
default: return new AllDiffPrecMoreThanBc(variables, precedence);
}
}
}
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