2005 | OriginalPaper | Buchkapitel
Towards an Optimal CNF Encoding of Boolean Cardinality Constraints
verfasst von : Carsten Sinz
Erschienen in: Principles and Practice of Constraint Programming - CP 2005
Verlag: Springer Berlin Heidelberg
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We consider the problem of encoding Boolean cardinality constraints in conjunctive normal form (CNF). Boolean cardinality constraints are formulae expressing that at most (resp. at least)
k
out of
n
propositional variables are true. We give two novel encodings that improve upon existing results, one which requires only 7
n
clauses and 2
n
auxiliary variables, and another one demanding
$\mathcal{O}(n \cdot k)$
clauses, but with the advantage that inconsistencies can be detected in linear time by unit propagation alone. Moreover, we prove a linear lower bound on the number of required clauses for any such encoding.