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
31 package org.sat4j.tools.encoding;
32
33 import org.sat4j.core.ConstrGroup;
34 import org.sat4j.core.VecInt;
35 import org.sat4j.specs.ContradictionException;
36 import org.sat4j.specs.IConstr;
37 import org.sat4j.specs.ISolver;
38 import org.sat4j.specs.IVecInt;
39
40 /**
41 * Binomial encoding for the "at most one" and "at most k" cases.
42 *
43 * For the "at most one" case, this encoding is equivalent to the one referred
44 * to in the literature as the pair-wise or naive encoding. For the "at most k"
45 * case, the previous encoding is generalized with binomial selection (see A. M.
46 * Frisch and P. A. Giannaros, "SAT Encodings of the At-Most-k Constraint", in
47 * International Workshop on Modelling and Reformulating Constraint Satisfaction
48 * Problems, 2010 for details).
49 *
50 * @author stephanieroussel
51 * @since 2.3.1
52 */
53 public class Binomial extends EncodingStrategyAdapter {
54
55 /**
56 *
57 */
58 private static final long serialVersionUID = 1L;
59
60 @Override
61 public IConstr addAtMost(ISolver solver, IVecInt literals, int degree)
62 throws ContradictionException {
63 ConstrGroup group = new ConstrGroup();
64
65 IVecInt clause = new VecInt();
66
67 if (degree == 1) {
68 return addAtMostOne(solver, literals);
69 }
70
71 for (IVecInt vec : literals.subset(degree + 1)) {
72 for (int i = 0; i < vec.size(); i++) {
73 clause.push(-vec.get(i));
74 }
75 group.add(solver.addClause(clause));
76 clause.clear();
77 }
78 return group;
79
80 }
81
82 @Override
83 public IConstr addAtMostOne(ISolver solver, IVecInt literals)
84 throws ContradictionException {
85 ConstrGroup group = new ConstrGroup();
86
87 IVecInt clause = new VecInt();
88
89 for (int i = 0; i < literals.size() - 1; i++) {
90 for (int j = i + 1; j < literals.size(); j++) {
91 clause.push(-literals.get(i));
92 clause.push(-literals.get(j));
93 group.add(solver.addClause(clause));
94 clause.clear();
95 }
96 }
97 return group;
98 }
99
100 @Override
101 public IConstr addExactlyOne(ISolver solver, IVecInt literals)
102 throws ContradictionException {
103 ConstrGroup group = new ConstrGroup();
104
105 group.add(addAtLeastOne(solver, literals));
106 group.add(addAtMostOne(solver, literals));
107
108 return group;
109 }
110
111 @Override
112 public IConstr addExactly(ISolver solver, IVecInt literals, int degree)
113 throws ContradictionException {
114 ConstrGroup group = new ConstrGroup();
115
116 group.add(addAtLeast(solver, literals, degree));
117 group.add(addAtMost(solver, literals, degree));
118
119 return group;
120 }
121
122 }