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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.sat;
import gnu.trove.map.hash.TIntIntHashMap;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.search.loop.monitors.NogoodFromRestarts;
import org.chocosolver.solver.variables.Variable;
/**
* This class manages no-goods sharing among models involved in a {@link
* org.chocosolver.solver.ParallelPortfolio}. In this, we make the following hypothesis: all models
* were created following the very same steps. The consequence is that a variable has the same ID in
* all models.
*
* Project: choco.
*
* @author Charles Prud'homme
* @since 10/02/2020.
*/
public class NogoodStealer {
/**
* A singleton that steals nothing
*/
public static final NogoodStealer NONE = new NogoodStealer() {
@Override
public void add(Model model) {
// void
}
@Override
public synchronized void nogoodStealing(Model model, NogoodFromRestarts caller) {
// void
}
@Override
public V getById(V var, Model model) {
return var;
}
};
/**
* List of models to steal nogoods from
*/
private final List models;
/**
* Maintain relation between id of a variable and its position in a model.
* @implSpec This is a strong assumption that all models are equivalent (ie, each variable
* has the same ID among models).
*/
private final TIntIntHashMap id2pos;
/**
* Create a class that steal nogoods (based on decision path) from models and store them in
* another one.
*/
public NogoodStealer() {
this.models = new ArrayList<>();
this.id2pos = new TIntIntHashMap(10,.5f,-1,-1);
}
/**
* Add a model to steal nogood from (based on decision path)
* @param model
*/
public void add(Model model) {
assert valid(model): "Cannot share nogoods between non equivalent models";
this.models.add(model);
}
private boolean valid(Model model) {
if (this.models.size() > 0) {
Variable[] vars0 = this.models.get(0).getVars();
Variable[] vars1 = model.getVars();
if (vars0.length == vars1.length) {
for (int i = 0; i < vars0.length; i++) {
if (vars0[i].getId() != vars1[i].getId()
|| !vars0[i].getName().equals(vars1[i].getName())
|| vars0[i].getNbProps() != vars1[i].getNbProps()
) {
return false;
}
}
} else {
return false;
}
}
return true;
}
/**
* Extract nogoods from decision paths of all models but model.
* @param model the model to skip
* @param caller nogoods extractor
*/
public synchronized void nogoodStealing(Model model, NogoodFromRestarts caller) {
for (Model m : models) {
if (m != model) {
caller.extractNogoodFromPath(m.getSolver().getDecisionPath());
}
}
}
/**
* @param type of variable to find
* @param var variable to look for (based on its ID)
* @param model prop
* @return the variable equivalent to var to declared in png
* (ie, from another model)
*/
public V getById(V var, Model model) {
int p = id2pos.get(var.getId());
if(p == -1){
p = binarySearch(model, var.getId());
}
//noinspection unchecked
return (V) model.getVar(p);
}
/**
* Adapted from {@link java.util.Arrays#binarySearch(Object[], Object, Comparator)}
*/
private static int binarySearch(Model model, int key) {
int low = 0;
int high = model.getNbVars();
while (low <= high) {
int mid = (low + high) >>> 1;
Variable midVal = model.getVar(mid);
int cmp = midVal.getId() - key;
if (cmp < 0) {
low = mid + 1;
} else if (cmp > 0) {
high = mid - 1;
} else {
return mid; // key found
}
}
return -(low + 1); // key not found.
}
}