期刊名称：Chicago Journal of Theoretical Computer Science
印刷版ISSN：1073-0486
出版年度：1999
卷号：1999
出版社：MIT Press ; University of Chicago, Department of Computer Science
摘要：In this paper, we prove a lemma that shows how to encode satisfying solutions of a k-CNF (boolean formulae in conjunctive normal form with at most k literals per clause) succinctly. Using this lemma, which we call the satisfiability coding lemma, we prove tight lower bounds on depth-3 circuits and improved upper bounds for the k-SAT problem. We show an Omega(n^{1/4}2^{\sqrt{n}}) lower bound on the size of depth-3 circuits of AND, OR, NOT gates computing the parity function. This bound is tight up to a constant factor. We also present and analyze two simple algorithms for finding satisfying assignments of k-CNFs. The first is a randomized algorithm which, with probability approaching 1, finds a satisfying assignment of a satisfiable k-CNF formula F in time O(n^2 |F| 2^{n-n/k}). The second algorithm is deterministic, and its running time approaches 2^{n-n/2k} for large n and k. The randomized algorithm improves on previous algorithms for k>3, though subsequent algorithms improve on it; the deterministic algorithm is the best known deterministic algorithm for k>4.
