/**
* Copyright (c) 1999-2014, Ecole des Mines de Nantes
* All rights reserved.
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* modification, are permitted provided that the following conditions are met:
*
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* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
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* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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package solver.search.strategy.strategy;
import solver.Solver;
import solver.exception.ContradictionException;
import solver.search.loop.monitors.IMonitorContradiction;
import solver.search.loop.monitors.IMonitorRestart;
import solver.search.loop.monitors.IMonitorSolution;
import solver.search.strategy.decision.Decision;
import solver.variables.Variable;
/**
* Last Conflict heuristic
* Composite heuristic which hacks a mainStrategy by forcing the
* use of variables involved in recent conflicts
*
* @author Jean-Guillaume Fages, Charles Prud'homme
*/
public class LastConflict extends AbstractStrategy<Variable> implements IMonitorRestart, IMonitorSolution, IMonitorContradiction {
//***********************************************************************************
// VARIABLES
//***********************************************************************************
protected Solver solver;
protected AbstractStrategy<Variable> mainStrategy;
protected boolean active;
protected int nbCV;
protected Variable[] conflictingVariables;
//***********************************************************************************
// CONSTRUCTORS
//***********************************************************************************
public LastConflict(Solver solver, AbstractStrategy<Variable> mainStrategy, int k) {
super(mainStrategy.vars);
assert k>0 : "parameter K of last conflict must be strictly positive!";
this.solver = solver;
this.mainStrategy = mainStrategy;
solver.getSearchLoop().plugSearchMonitor(this);
conflictingVariables = new Variable[k];
nbCV = 0;
active = false;
}
//***********************************************************************************
// METHODS
//***********************************************************************************
@Override
public void init() throws ContradictionException {
mainStrategy.init();
}
@Override
public Decision getDecision() {
if(active){
Variable decVar = firstNotInst();
if (decVar != null) {
Decision d = mainStrategy.computeDecision(decVar);
if(d != null){
return d;
}
}
}
active = true;
return mainStrategy.getDecision();
}
//***********************************************************************************
// Monitor
//***********************************************************************************
@Override
public void onContradiction(ContradictionException cex) {
Variable curDecVar = solver.getSearchLoop().getLastDecision().getDecisionVariable();
if(nbCV>0 && conflictingVariables[nbCV-1]==curDecVar)return;
if(inScope(curDecVar)){
if(nbCV<conflictingVariables.length){
conflictingVariables[nbCV++] = curDecVar;
}else{
assert nbCV==conflictingVariables.length;
for(int i=0;i<nbCV-1;i++){
conflictingVariables[i] = conflictingVariables[i+1];
}
conflictingVariables[nbCV-1] = curDecVar;
}
}
}
@Override
public void beforeRestart() {}
@Override
public void afterRestart() {
active = false;
}
@Override
public void onSolution() {
active = false;
}
//***********************************************************************************
//***********************************************************************************
private Variable firstNotInst() {
for(int i=nbCV-1;i>=0;i--){
if(!conflictingVariables[i].isInstantiated()){
return conflictingVariables[i];
}
}
return null;
}
private boolean inScope(Variable target){
Variable[] scope = mainStrategy.vars;
for(int v=0; v<scope.length; v++){
if(scope[v].getId()==target.getId()){
return true;
}
}
return false;
}
}