1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004, 2012 Artois University and CNRS
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 * Contributors:
28 * CRIL - initial API and implementation
29 *******************************************************************************/
30 package org.sat4j.tools;
31
32 import org.sat4j.core.VecInt;
33 import org.sat4j.specs.ContradictionException;
34 import org.sat4j.specs.ISolver;
35 import org.sat4j.specs.IVecInt;
36 import org.sat4j.specs.TimeoutException;
37
38 /**
39 * Another solver decorator that counts the number of solutions.
40 *
41 * Note that this approach is quite naive so do not expect it to work on large
42 * examples. The number of solutions will be wrong if the SAT solver does not
43 * provide a complete assignment.
44 *
45 * The class is expected to be used that way:
46 *
47 * <pre>
48 * SolutionCounter counter = new SolverCounter(SolverFactory.newDefault());
49 * try {
50 * int nbSol = counter.countSolutions();
51 * // the exact number of solutions is nbSol
52 * ...
53 * } catch (TimeoutException te) {
54 * int lowerBound = counter.lowerBound();
55 * // the solver found lowerBound solutions so far.
56 * ...
57 * }
58 * </pre>
59 *
60 * @author leberre
61 *
62 */
63 public class SolutionCounter extends SolverDecorator<ISolver> {
64
65 /**
66 *
67 */
68 private static final long serialVersionUID = 1L;
69
70 private int lowerBound;
71
72 public SolutionCounter(ISolver solver) {
73 super(solver);
74 }
75
76 /**
77 * Get the number of solutions found before the timeout occurs.
78 *
79 * @return the number of solutions found so far.
80 * @since 2.1
81 */
82 public int lowerBound() {
83 return this.lowerBound;
84 }
85
86 /**
87 * Naive approach to count the solutions available in a boolean formula:
88 * each time a solution is found, a new clause is added to prevent it to be
89 * found again.
90 *
91 * @return the number of solution found.
92 * @throws TimeoutException
93 * if the timeout given to the solver is reached.
94 */
95 public long countSolutions() throws TimeoutException {
96 this.lowerBound = 0;
97 boolean trivialfalsity = false;
98
99 while (!trivialfalsity && isSatisfiable(true)) {
100 this.lowerBound++;
101 int[] last = model();
102 IVecInt clause = new VecInt(last.length);
103 for (int q : last) {
104 clause.push(-q);
105 }
106 try {
107 addClause(clause);
108 } catch (ContradictionException e) {
109 trivialfalsity = true;
110 }
111 }
112 return this.lowerBound;
113 }
114 }