/*******************************************************************************
* 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.ISolver;
import org.sat4j.specs.IVecInt;
import org.sat4j.specs.TimeoutException;
/**
* Another solver decorator that counts the number of solutions.
*
* Note that this approach is quite naive so do not expect it to work on large
* examples. The number of solutions will be wrong if the SAT solver
* does not provide a complete assignment.
*
* The class is expected to be used that way:
*
* <pre>
* SolutionCounter counter = new SolverCounter(SolverFactory.newDefault());
* try {
* int nbSol = counter.countSolutions();
* // the exact number of solutions is nbSol
* ...
* } catch (TimeoutException te) {
* int lowerBound = counter.lowerBound();
* // the solver found lowerBound solutions so far.
* ...
* }
* </pre>
*
* @author leberre
*
*/
public class SolutionCounter extends SolverDecorator<ISolver> {
/**
*
*/
private static final long serialVersionUID = 1L;
private int lowerBound;
public SolutionCounter(ISolver solver) {
super(solver);
}
/**
* Get the number of solutions found before the timeout occurs.
*
* @return the number of solutions found so far.
*/
public int lowerBound() {
return lowerBound;
}
/**
* Naive approach to count the solutions available in
* a boolean formula: each time a solution is found,
* a new clause is added to prevent it to be found again.
*
* @return the number of solution found.
* @throws TimeoutException if the timeout given to the solver is reached.
*/
public long countSolutions() throws TimeoutException {
lowerBound = 0;
boolean trivialfalsity = false;
while (!trivialfalsity && isSatisfiable(true)) {
lowerBound++;
int[] last = model();
IVecInt clause = new VecInt(last.length);
for (int q : last) {
clause.push(-q);
}
try {
// System.out.println("Sol number "+nbsols+" adding " + clause);
addClause(clause);
} catch (ContradictionException e) {
trivialfalsity = true;
}
}
return lowerBound;
}
}