Grundy Coloring and Friends, Half-Graphs, Bicliques
Aboulker, Pierre; Bonnet, Edouard; Kim, Eun Jung; Sikora, Florian (2023), Grundy Coloring and Friends, Half-Graphs, Bicliques, Algorithmica, 85, 1, p. 1-28. 10.1007/s00453-022-01001-2
Type
Article accepté pour publication ou publiéDate
2023Journal name
AlgorithmicaVolume
85Number
1Publisher
Springer
Pages
1-28
Publication identifier
Metadata
Show full item recordAuthor(s)
Aboulker, Pierre
Département d'informatique - ENS Paris [DI-ENS]
Bonnet, Edouard

Laboratoire de l'Informatique du Parallélisme [LIP]
Kim, Eun Jung
Laboratoire d'analyse et modélisation de systèmes pour l'aide à la décision [LAMSADE]
Sikora, Florian

Laboratoire d'analyse et modélisation de systèmes pour l'aide à la décision [LAMSADE]
Abstract (EN)
The first-fit coloring is a heuristic that assigns to each vertex, arriving in a specified order σ, the smallest available color. The problem GRUNDY COLORING asks how many colors are needed for the most adversarial vertex ordering σ, i.e., the maximum number of colors that the first-fit coloring requires over all possible vertex orderings. Since its inception by Grundy in 1939, GRUNDY COLORING has been examined for its structural and algorithmic aspects. A brute-force f(k)n2k−1-time algorithm for GRUNDY COLORING on general graphs is not difficult to obtain, where k is the number of colors required by the most adversarial vertex ordering. It was asked several times whether the dependency on k in the exponent of n can be avoided or reduced, and its answer seemed elusive until now. We prove that GRUNDY COLORING is W[1]-hard and the brute-force algorithm is essentially optimal under the Exponential Time Hypothesis, thus settling this question by the negative. The key ingredient in our W[1]-hardness proof is to use so-called half-graphs as a building block to transmit a color from one vertex to another. Leveraging the half-graphs, we also prove that b-CHROMATIC CORE is W[1]-hard, whose parameterized complexity was posed as an open question by Panolan et al. [JCSS ’17]. A natural follow-up question is, how the parameterized complexity changes in the absence of (large) half-graphs. We establish fixed-parameter tractability on Kt,t-free graphs for b-CHROMATIC CORE and PARTIAL GRUNDY COLORING, making a step toward answering this question. The key combinatorial lemma underlying the tractability result might be of independent interest.Subjects / Keywords
Grundy coloring; Parameterized complexity; ETH lower bounds; Half-graphsRelated items
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