El Ouali, Mourad, Fohlin, Helena and Srivastav, Anand
(2014)
*A randomised approximation algorithm for the hitting set problem*
Theoretical Computer Science, 555
.
pp. 23-34.

## Abstract

Let H = (V, epsilon) be a hypergraph with vertex set V and edge set epsilon, where n := vertical bar V vertical bar and m := vertical bar epsilon vertical bar. Let l be the maximum size of an edge and Delta be the maximum vertex degree. A hitting set (or vertex cover) in H is a subset of V in which all edges are incident. The hitting set problem is to find a hitting set of minimum cardinality. It is known that an approximation ratio of l can be achieved easily. On the other hand, for constant l, an approximation ratio better than l cannot be achieved in polynomial time under the unique games conjecture (Khot and Regev, 2008 [17]). Thus breaking the l-barrier for significant classes of hypergraphs is a complexity-theoretically and algorithmically interesting problem, which has been studied by several authors (Krivelevich, 1997 [18], Halperin, 2000 [12], Okun, 2005 [23]). We propose a randomised algorithm of hybrid type for the hitting set problem, which combines LP-based randomised rounding, graphs sparsening and greedy repairing and analyse it for different classes of hypergraphs. For hypergraphs with Delta = O(n1/4) and l = O (root n) we achieve an approximation ratio of l(1 - c/Delta), for some constant c > 0, with constant probability. For the case of hypergraphs where l and Delta are constants, we prove a ratio of l(1 - l-1/8 Delta). The latter is done by analysing the expected size of the hitting set and using concentration inequalities. Moreover, for quasi-regularisable hypergraphs, we achieve an approximation ratio of l(1 - n/8m). We show how and when our results improve over the results of Krivelevich, Halperin and Okun. (C) 2014 Elsevier B.V. All rights reserved.

Document Type: | Article |
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Additional Information: | Times Cited: 0 0 |

Research affiliation: | Kiel University OceanRep > The Future Ocean - Cluster of Excellence > FO-R11 OceanRep > The Future Ocean - Cluster of Excellence |

Refereed: | Yes |

ISSN: | 0304-3975 |

Projects: | Future Ocean |

Date Deposited: | 30 Mar 2015 12:11 |

Last Modified: | 05 Apr 2017 06:51 |

URI: | http://eprints.uni-kiel.de/id/eprint/27485 |

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