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.IConstr;
33 import org.sat4j.specs.ISolver;
34 import org.sat4j.specs.IVecInt;
35 import org.sat4j.specs.TimeoutException;
36
37 /**
38 * This solver decorator allows to detect whether or not the set of constraints
39 * available in the solver has only one solution or not.
40 *
41 * NOTE THAT THIS DECORATOR CANNOT BE USED WITH SOLVERS USING SPECIFIC DATA
42 * STRUCTURES FOR BINARY OR TERNARY CLAUSES!
43 *
44 * <code>
45 SingleSolutionDetector problem =
46 new SingleSolutionDetector(SolverFactory.newMiniSAT());
47 // feed problem/solver as usual
48
49 if (problem.isSatisfiable()) {
50 if (problem.hasASingleSolution()) {
51 // great, the instance has a unique solution
52 int [] uniquesolution = problem.getModel();
53 } else {
54 // too bad, got more than one
55 }
56 }
57 * </code>
58 *
59 * @author leberre
60 *
61 */
62 public class SingleSolutionDetector extends SolverDecorator<ISolver> {
63
64 /**
65 *
66 */
67 private static final long serialVersionUID = 1L;
68
69 public SingleSolutionDetector(ISolver solver) {
70 super(solver);
71 }
72
73 /**
74 * Please use that method only after a positive answer from isSatisfiable()
75 * (else a runtime exception will be launched).
76 *
77 * NOTE THAT THIS FUNCTION SHOULD NOT ONLY BE USED ONCE THE FINAL SOLUTION IS FOUND,
78 * SINCE THE METHOD ADDS CONSTRAINTS INTO THE SOLVER THAT MAY NOT BE REMOVED UNDER
79 * CERTAIN CONDITIONS (UNIT CONSTRAINTS LEARNT FOR INSTANCE).
80 * THAT ISSUE WILL BE RESOLVED ONCE REMOVECONSTR WILL WORK PROPERLY.
81 *
82 * @return true iff there is only one way to satisfy all the constraints in
83 * the solver.
84 * @throws TimeoutException
85 * @see {@link ISolver#removeConstr(IConstr)}
86 */
87 public boolean hasASingleSolution() throws TimeoutException {
88 return hasASingleSolution(new VecInt());
89 }
90
91 /**
92 * Please use that method only after a positive answer from
93 * isSatisfiable(assumptions) (else a runtime exception will be launched).
94 *
95 * @param assumptions
96 * a set of literals (dimacs numbering) that must be satisfied.
97 * @return true iff there is only one way to satisfy all the constraints in
98 * the solver using the provided set of assumptions.
99 * @throws TimeoutException
100 */
101 public boolean hasASingleSolution(IVecInt assumptions)
102 throws TimeoutException {
103 int[] firstmodel = model();
104 assert firstmodel != null;
105 IVecInt clause = new VecInt(firstmodel.length);
106 for (int q : firstmodel) {
107 clause.push(-q);
108 }
109 boolean result = false;
110 try {
111 IConstr added = addClause(clause);
112 result = !isSatisfiable(assumptions);
113 removeConstr(added);
114 } catch (ContradictionException e) {
115 result = true;
116 }
117 return result;
118 }
119 }