The Upper Clique Transversal Problem

TL;DR

This paper introduces the upper clique transversal number, studying its computational complexity across various graph classes, revealing NP-completeness in some and polynomial-time solvability in others.

Contribution

It defines the upper clique transversal number and analyzes its complexity, providing new insights into its algorithmic properties across different graph classes.

Findings

NP-complete in chordal and bipartite graphs

Linear time solvable in split, interval, and cographs

Polynomial time for graphs of bounded cliquewidth

Abstract

A clique transversal in a graph is a set of vertices intersecting all maximal cliques. The problem of determining the minimum size of a clique transversal has received considerable attention in the literature. In this paper, we initiate the study of the ''upper'' variant of this parameter, the upper clique transversal number, defined as the maximum size of a minimal clique transversal. We investigate this parameter from the algorithmic and complexity points of view, with a focus on various graph classes. We show that the corresponding decision problem is NP-complete in the classes of chordal graphs, chordal bipartite graphs, cubic planar bipartite graphs, and line graphs of bipartite graphs, but solvable in linear time in the classes of split graphs, proper interval graphs, and cographs, and in polynomial time for graphs of bounded cliquewidth. We conclude the paper with a number of open questions.