On the tractability of (k,i)-coloring

Abstract

In an undirected graph, a proper (k,i)-coloring is an assignment of a set of k colors to each vertex such that any two adjacent vertices have at most i common colors. The (k,i)-coloring problem is to compute the minimum number of colors required for a proper (k,i)-coloring. This is a generalization of the classical graph coloring problem. We design a parameterized algorithm for the (k,i)-coloring problem with the size of the feedback vertex set as a parameter. Our algorithm does not use tree-width machinery, thus answering a question of Majumdar, Neogi, Raman and Tale [CALDAM 2017]. We also give a faster exact algorithm for (k,k−1)-coloring. From the hardness perspective, we show that the (k,i)-coloring problem is NP-complete for any fixed values i,k, whenever i < k, thereby settling a conjecture of Méndez-Díaz and Zabala (1999) and again asked by Majumdar, Neogi, Raman and Tale. The NP-completeness result improves the partial NP-completeness shown in the preliminary version of this paper published in CALDAM 2018.