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.IConstr;
35 import org.sat4j.specs.ISolver;
36 import org.sat4j.specs.IVecInt;
37 import org.sat4j.specs.TimeoutException;
38
39 /**
40 * This solver decorator allows to detect whether or not the set of constraints
41 * available in the solver has only one solution or not.
42 *
43 * NOTE THAT THIS DECORATOR CANNOT BE USED WITH SOLVERS USING SPECIFIC DATA
44 * STRUCTURES FOR BINARY OR TERNARY CLAUSES!
45 *
46 * <code>
47 SingleSolutionDetector problem =
48 new SingleSolutionDetector(SolverFactory.newMiniSAT());
49 // feed problem/solver as usual
50
51 if (problem.isSatisfiable()) {
52 if (problem.hasASingleSolution()) {
53 // great, the instance has a unique solution
54 int [] uniquesolution = problem.getModel();
55 } else {
56 // too bad, got more than one
57 }
58 }
59 * </code>
60 *
61 * @author leberre
62 *
63 */
64 public class SingleSolutionDetector extends SolverDecorator<ISolver> {
65
66 /**
67 *
68 */
69 private static final long serialVersionUID = 1L;
70
71 public SingleSolutionDetector(ISolver solver) {
72 super(solver);
73 }
74
75 /**
76 * Please use that method only after a positive answer from isSatisfiable()
77 * (else a runtime exception will be launched).
78 *
79 * NOTE THAT THIS FUNCTION SHOULD NOT ONLY BE USED ONCE THE FINAL SOLUTION
80 * IS FOUND, SINCE THE METHOD ADDS CONSTRAINTS INTO THE SOLVER THAT MAY NOT
81 * BE REMOVED UNDER CERTAIN CONDITIONS (UNIT CONSTRAINTS LEARNT FOR
82 * INSTANCE). THAT ISSUE WILL BE RESOLVED ONCE REMOVECONSTR WILL WORK
83 * PROPERLY.
84 *
85 * @return true iff there is only one way to satisfy all the constraints in
86 * the solver.
87 * @throws TimeoutException
88 * @see {@link ISolver#removeConstr(IConstr)}
89 */
90 public boolean hasASingleSolution() throws TimeoutException {
91 return hasASingleSolution(new VecInt());
92 }
93
94 /**
95 * Please use that method only after a positive answer from
96 * isSatisfiable(assumptions) (else a runtime exception will be launched).
97 *
98 * @param assumptions
99 * a set of literals (dimacs numbering) that must be satisfied.
100 * @return true iff there is only one way to satisfy all the constraints in
101 * the solver using the provided set of assumptions.
102 * @throws TimeoutException
103 */
104 public boolean hasASingleSolution(IVecInt assumptions)
105 throws TimeoutException {
106 int[] firstmodel = model();
107 assert firstmodel != null;
108 IVecInt clause = new VecInt(firstmodel.length);
109 for (int q : firstmodel) {
110 clause.push(-q);
111 }
112 boolean result = false;
113 try {
114 IConstr added = addClause(clause);
115 result = !isSatisfiable(assumptions);
116 removeConstr(added);
117 } catch (ContradictionException e) {
118 result = true;
119 }
120 return result;
121 }
122 }