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A b-coloring of a graph is a proper vertex coloring such that each color class contains a vertex that sees all other colors in its neighborhood. The b-coloring problem, in which the task is to decide whether a graph admits a b-coloring with k colors, is NP-complete in general but polytime solvable on trees. Moreover, it is known that b-coloring is in XP but W[t]-hard for all t ∈ ℕ when parameterized by tree-width. In fact, only very few parameters, such as the vertex cover number, were known to admit an FPT algorithm for b-coloring. In this paper, we consider a more restrictive parameter measuring similarity to trees than tree-width, namely the feedback edge number, and show that b-coloring is fixed-parameter tractable under this parameterization. Our algorithm combines standard techniques used in parameterized algorithmics with the problem-specific ideas used in the polytime algorithm for trees. In addition, we present an FPT algorithm for b-coloring parameterized by distance to co-cluster, which is a parameter measuring similarity to complete multipartite graphs. Finally, we make several observations based on known results, including that b-coloring is W[1]-hard when parameterized by tree-depth.
@InProceedings{balaban:LIPIcs.MFCS.2026.36,
author = {Balab\'{a}n, Jakub},
title = {{Finding b-Colorings Using Feedback Edges}},
booktitle = {51st International Symposium on Mathematical Foundations of Computer Science (MFCS 2026)},
pages = {36:1--36:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-442-0},
ISSN = {1868-8969},
year = {2026},
volume = {386},
editor = {Kouck\'{y}, Michal and Petrișan, Daniela},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2026.36},
URN = {urn:nbn:de:0030-drops-274172},
doi = {10.4230/LIPIcs.MFCS.2026.36},
annote = {Keywords: b-coloring, fixed-parameter algorithms, feedback edge number, distance to co-cluster}
}