On Structural Parameterizations of Hitting Set: Hitting Paths in Graphs Using 2-SAT

  • Bart M. P. JansenEmail author
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9224)


Hitting Set is a classic problem in combinatorial optimization. Its input consists of a set system \(\mathcal {F} \) over a finite universe U and an integer t; the question is whether there is a set of t elements that intersects every set in \(\mathcal {F} \). The Hitting Set problem parameterized by the size of the solution is a well-known W[2]-complete problem in parameterized complexity theory. In this paper we investigate the complexity of Hitting Set under various structural parameterizations of the input. Our starting point is the folklore result that Hitting Set is polynomial-time solvable if there is a tree T on vertex set U such that the sets in \(\mathcal {F} \) induce connected subtrees of T. We consider the case that there is a treelike graph with vertex set U such that the sets in \(\mathcal {F} \) induce connected subgraphs; the parameter of the problem is a measure of how treelike the graph is. Our main positive result is an algorithm that, given a graph G with cyclomatic number k, a collection \(\mathcal {P} \) of simple paths in G, and an integer t, determines in time \(2^{5k} (|G| +|\mathcal {P} |)^{{\mathcal {O}}(1)}\) whether there is a vertex set of size t that hits all paths in \(\mathcal {P} \). It is based on a connection to the 2-SAT problem in multiple valued logic. For other parameterizations we derive W[1]-hardness and para-NP-completeness results.



We are grateful to Mark de Berg and Kevin Buchin for interesting discussions that triggered this research.


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© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Eindhoven University of TechnologyEindhovenThe Netherlands

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