1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
3 *
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
8 *
9 * Alternatively, the contents of this file may be used under the terms of
10 * either the GNU Lesser General Public License Version 2.1 or later (the
11 * "LGPL"), in which case the provisions of the LGPL are applicable instead
12 * of those above. If you wish to allow use of your version of this file only
13 * under the terms of the LGPL, and not to allow others to use your version of
14 * this file under the terms of the EPL, indicate your decision by deleting
15 * the provisions above and replace them with the notice and other provisions
16 * required by the LGPL. If you do not delete the provisions above, a recipient
17 * may use your version of this file under the terms of the EPL or the LGPL.
18 *
19 * Based on the original MiniSat specification from:
20 *
21 * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
22 * Sixth International Conference on Theory and Applications of Satisfiability
23 * Testing, LNCS 2919, pp 502-518, 2003.
24 *
25 * See www.minisat.se for the original solver in C++.
26 *
27 *******************************************************************************/
28 package org.sat4j.tools;
29
30 import org.sat4j.core.VecInt;
31 import org.sat4j.specs.ContradictionException;
32 import org.sat4j.specs.ISolver;
33 import org.sat4j.specs.IVecInt;
34 import org.sat4j.specs.TimeoutException;
35
36 /**
37 * Another solver decorator that counts the number of solutions.
38 *
39 * Note that this approach is quite naive so do not expect it to work on large
40 * examples. The number of solutions will be wrong if the SAT solver does not
41 * provide a complete assignment.
42 *
43 * The class is expected to be used that way:
44 *
45 * <pre>
46 * SolutionCounter counter = new SolverCounter(SolverFactory.newDefault());
47 * try {
48 * int nbSol = counter.countSolutions();
49 * // the exact number of solutions is nbSol
50 * ...
51 * } catch (TimeoutException te) {
52 * int lowerBound = counter.lowerBound();
53 * // the solver found lowerBound solutions so far.
54 * ...
55 * }
56 * </pre>
57 *
58 * @author leberre
59 *
60 */
61 public class SolutionCounter extends SolverDecorator<ISolver> {
62
63 /**
64 *
65 */
66 private static final long serialVersionUID = 1L;
67
68 private int lowerBound;
69
70 public SolutionCounter(ISolver solver) {
71 super(solver);
72 }
73
74 /**
75 * Get the number of solutions found before the timeout occurs.
76 *
77 * @return the number of solutions found so far.
78 * @since 2.1
79 */
80 public int lowerBound() {
81 return lowerBound;
82 }
83
84 /**
85 * Naive approach to count the solutions available in a boolean formula:
86 * each time a solution is found, a new clause is added to prevent it to be
87 * found again.
88 *
89 * @return the number of solution found.
90 * @throws TimeoutException
91 * if the timeout given to the solver is reached.
92 */
93 public long countSolutions() throws TimeoutException {
94 lowerBound = 0;
95 boolean trivialfalsity = false;
96
97 while (!trivialfalsity && isSatisfiable(true)) {
98 lowerBound++;
99 int[] last = model();
100 IVecInt clause = new VecInt(last.length);
101 for (int q : last) {
102 clause.push(-q);
103 }
104 try {
105 // System.out.println("Sol number "+nbsols+" adding " + clause);
106 addClause(clause);
107 } catch (ContradictionException e) {
108 trivialfalsity = true;
109 }
110 }
111 return lowerBound;
112 }
113 }