Short and local transformations between ($\Delta +1$)-colorings
Innovations in Graph Theory, Volume 2 (2025), pp. 119-156

Recoloring a graph is about finding a sequence of proper colorings of this graph from an initial coloring $\sigma $ to a target coloring $\eta $. Adding the constraint that each pair of consecutive colorings must differ on exactly one vertex, one asks: Is there a sequence of colorings from $\sigma $ to $\eta $? If yes, how short can it be?

In this paper, we focus on $(\Delta +1)$-colorings of graphs of maximum degree $\Delta $. Feghali, Johnson and Paulusma proved that, if both colorings are unfrozen (i.e. if we can change the color of at least one vertex), then a recoloring sequence of length at most quadratic in the size of the graph always exists. We improve their result by proving that there actually exists a linear transformation (assuming that $\Delta $ is a constant).

In addition, we prove that the core of our algorithm can be performed locally. Informally, this means that after some preprocessing, the color changes that a given vertex has to perform only depend on the colors of the vertices in a constant size neighborhood. We make this precise by designing of an efficient recoloring algorithm in the LOCAL model of distributed computing.

Received:
Accepted:
Published online:
DOI: 10.5802/igt.8
Keywords: Graph reconfiguration, recoloring, linear transformation, unfrozen colorings, distributed algorithms.

Bousquet, Nicolas 1; Feuilloley, Laurent 1; Heinrich, Marc 2; Rabie, Mikaël 3

1 CNRS, INSA Lyon, UCBL, LIRIS, UMR5205, F-69621, Lyon, France
2 Leeds University, UK
3 Université Paris Cité, CNRS, IRIF, F-75013, Paris, France
License: CC-BY 4.0
Copyrights: The authors retain unrestricted copyrights and publishing rights
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Bousquet, Nicolas; Feuilloley, Laurent; Heinrich, Marc; Rabie, Mikaël. Short and local transformations between ($\Delta +1$)-colorings. Innovations in Graph Theory, Volume 2 (2025), pp. 119-156. doi: 10.5802/igt.8

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