/*******************************************************************************
* SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU Lesser General Public License Version 2.1 or later (the
* "LGPL"), in which case the provisions of the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of the LGPL, and not to allow others to use your version of
* this file under the terms of the EPL, indicate your decision by deleting
* the provisions above and replace them with the notice and other provisions
* required by the LGPL. If you do not delete the provisions above, a recipient
* may use your version of this file under the terms of the EPL or the LGPL.
*
* Based on the original MiniSat specification from:
*
* An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
* Sixth International Conference on Theory and Applications of Satisfiability
* Testing, LNCS 2919, pp 502-518, 2003.
*
* See www.minisat.se for the original solver in C++.
*
*******************************************************************************/
package org.sat4j.tools;
import org.sat4j.core.VecInt;
import org.sat4j.specs.ContradictionException;
import org.sat4j.specs.IConstr;
import org.sat4j.specs.ISolver;
import org.sat4j.specs.IVecInt;
import org.sat4j.specs.TimeoutException;
/**
* This solver decorator allows to detect whether or not the set of constraints
* available in the solver has only one solution or not.
*
* NOTE THAT THIS DECORATOR CANNOT BE USED WITH SOLVERS USING SPECIFIC DATA
* STRUCTURES FOR BINARY OR TERNARY CLAUSES!
*
* <code>
SingleSolutionDetector problem =
new SingleSolutionDetector(SolverFactory.newMiniSAT());
// feed problem/solver as usual
if (problem.isSatisfiable()) {
if (problem.hasASingleSolution()) {
// great, the instance has a unique solution
int [] uniquesolution = problem.getModel();
} else {
// too bad, got more than one
}
}
* </code>
*
* @author leberre
*
*/
public class SingleSolutionDetector extends SolverDecorator<ISolver> {
/**
*
*/
private static final long serialVersionUID = 1L;
public SingleSolutionDetector(ISolver solver) {
super(solver);
}
/**
* Please use that method only after a positive answer from isSatisfiable()
* (else a runtime exception will be launched).
*
* NOTE THAT THIS FUNCTION SHOULD NOT ONLY BE USED ONCE THE FINAL SOLUTION IS FOUND,
* SINCE THE METHOD ADDS CONSTRAINTS INTO THE SOLVER THAT MAY NOT BE REMOVED UNDER
* CERTAIN CONDITIONS (UNIT CONSTRAINTS LEARNT FOR INSTANCE).
* THAT ISSUE WILL BE RESOLVED ONCE REMOVECONSTR WILL WORK PROPERLY.
*
* @return true iff there is only one way to satisfy all the constraints in
* the solver.
* @throws TimeoutException
* @see {@link ISolver#removeConstr(IConstr)}
*/
public boolean hasASingleSolution() throws TimeoutException {
return hasASingleSolution(new VecInt());
}
/**
* Please use that method only after a positive answer from
* isSatisfiable(assumptions) (else a runtime exception will be launched).
*
* @param assumptions
* a set of literals (dimacs numbering) that must be satisfied.
* @return true iff there is only one way to satisfy all the constraints in
* the solver using the provided set of assumptions.
* @throws TimeoutException
*/
public boolean hasASingleSolution(IVecInt assumptions)
throws TimeoutException {
int[] firstmodel = model();
assert firstmodel != null;
IVecInt clause = new VecInt(firstmodel.length);
for (int q : firstmodel) {
clause.push(-q);
}
boolean result = false;
try {
IConstr added = addClause(clause);
result = !isSatisfiable(assumptions);
removeConstr(added);
} catch (ContradictionException e) {
result = true;
}
return result;
}
}