Abstract
Given a graph G, a properk-coloring of G is a partition \(c = (S_i)_{i\in [1,k]}\) of V(G) into k stable sets \(S_1,\ldots , S_{k}\). Given a weight function \(w: V(G) \rightarrow {\mathbb {R}}^+\), the weight of a color\(S_i\) is defined as \(w(i) = \max _{v \in S_i} w(v)\) and the weight of a coloringc as \(w(c) = \sum _{i=1}^{k}w(i)\). Guan and Zhu (Inf Process Lett 61(2):77–81, 1997) defined the weighted chromatic number of a pair (G, w), denoted by \(\sigma (G,w)\), as the minimum weight of a proper coloring of G. The problem of determining \(\sigma (G,w)\) has received considerable attention during the last years, and has been proved to be notoriously hard: for instance, it is NP-hard on split graphs, unsolvable on n-vertex trees in time \(n^{o(\log n)}\) unless the ETH fails, and W[1]-hard on forests parameterized by the size of a largest tree. We focus on the so-called dual parameterization of the problem: given a vertex-weighted graph (G, w) and an integer k, is \(\sigma (G,w) \le \sum _{v \in V(G)} w(v) - k\)? This parameterization has been recently considered by Escoffier (in: Proceedings of the 42nd international workshop on graph-theoretic concepts in computer science (WG). LNCS, vol 9941, pp 50–61, 2016), who provided an FPT algorithm running in time \(2^{{\mathcal {O}}(k \log k)} \cdot n^{{\mathcal {O}}(1)}\), and asked which kernel size can be achieved for the problem. We provide an FPT algorithm in time \(9^k \cdot n^{{\mathcal {O}}(1)}\), and prove that no algorithm in time \(2^{o(k)} \cdot n^{{\mathcal {O}}(1)}\) exists under the ETH. On the other hand, we present a kernel with at most \((2^{k-1}+1) (k-1)\) vertices, and rule out the existence of polynomial kernels unless \(\mathsf{NP} \subseteq \mathsf{coNP} / \mathsf{poly}\), even on split graphs with only two different weights. Finally, we identify classes of graphs allowing for polynomial kernels, namely interval graphs, comparability graphs, and subclasses of circular-arc and split graphs, and in the latter case we present lower bounds on the degrees of the polynomials.
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Funding
Work supported by French Projects DEMOGRAPH (ANR-16-CE40-0028) and ESIGMA (ANR-17-CE23-0010), and by Brazilian Projects CNPq 306262/2014-2, CNPq 311013/2015-5, CNPq Universal 421660/2016-3, CNPq Universal 401519/2016-3, FAPEMIG, Funcap PNE-0112-00061.01.00/16, and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001.
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This article is permanently available at [arXiv:1805.06699]. A conference version appeared in the Proc. of the 13th International Symposium on Parameterized and Exact Computation (IPEC), volume 115 of LIPIcs, pages 12:1–12:14, Helsinki, Finland, August 2018.
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Araújo, J., Campos, V.A., Lima, C.V.G.C. et al. Dual Parameterization of Weighted Coloring. Algorithmica 82, 2316–2336 (2020). https://doi.org/10.1007/s00453-020-00686-7
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DOI: https://doi.org/10.1007/s00453-020-00686-7
Keywords
- Weighted coloring
- Max coloring
- Parameterized complexity
- Dual parameterization
- FPT algorithms
- Polynomial kernels
- Split graphs
- Interval graphs