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 @Override
56 public IConstr addAtMost(ISolver solver, IVecInt literals, int degree)
57 throws ContradictionException {
58 ConstrGroup group = new ConstrGroup();
59
60 IVecInt clause = new VecInt();
61
62 if (degree == 1) {
63 return addAtMostOne(solver, literals);
64 }
65
66 for (IVecInt vec : literals.subset(degree + 1)) {
67 for (int i = 0; i < vec.size(); i++) {
68 clause.push(-vec.get(i));
69 }
70 group.add(solver.addClause(clause));
71 clause.clear();
72 }
73 return group;
74
75 }
76
77 @Override
78 public IConstr addAtMostOne(ISolver solver, IVecInt literals)
79 throws ContradictionException {
80 ConstrGroup group = new ConstrGroup();
81
82 IVecInt clause = new VecInt();
83
84 for (int i = 0; i < literals.size() - 1; i++) {
85 for (int j = i + 1; j < literals.size(); j++) {
86 clause.push(-literals.get(i));
87 clause.push(-literals.get(j));
88 group.add(solver.addClause(clause));
89 clause.clear();
90 }
91 }
92 return group;
93 }
94
95 @Override
96 public IConstr addExactlyOne(ISolver solver, IVecInt literals)
97 throws ContradictionException {
98 ConstrGroup group = new ConstrGroup();
99
100 group.add(addAtLeastOne(solver, literals));
101 group.add(addAtMostOne(solver, literals));
102
103 return group;
104 }
105
106 @Override
107 public IConstr addExactly(ISolver solver, IVecInt literals, int degree)
108 throws ContradictionException {
109 ConstrGroup group = new ConstrGroup();
110
111 group.add(addAtLeast(solver, literals, degree));
112 group.add(addAtMost(solver, literals, degree));
113
114 return group;
115 }
116
117 @Override
118 public IConstr addAtLeast(ISolver solver, IVecInt literals, int degree)
119 throws ContradictionException {
120 if (degree == 1) {
121 return addAtLeastOne(solver, literals);
122 }
123
124 IVecInt negLiterals = new VecInt();
125
126 for (int i = 0; i < literals.size(); i++) {
127 negLiterals.push(-literals.get(i));
128 }
129
130 return addAtMost(solver, negLiterals, literals.size() - degree);
131 }
132
133 @Override
134 public IConstr addAtLeastOne(ISolver solver, IVecInt literals)
135 throws ContradictionException {
136 ConstrGroup group = new ConstrGroup();
137 IVecInt clause = new VecInt();
138
139 for (int i = 0; i < literals.size(); i++) {
140 clause.push(literals.get(i));
141 }
142 group.add(solver.addClause(clause));
143
144 return group;
145 }
146 }