Algorithms for Coloring Reconfiguration Under Recolorability Constraints

Authors Hiroki Osawa, Akira Suzuki , Takehiro Ito , Xiao Zhou

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Author Details

Hiroki Osawa
  • Graduate School of Information Sciences, Tohoku University, Japan
Akira Suzuki
  • Graduate School of Information Sciences, Tohoku University, Japan
Takehiro Ito
  • Graduate School of Information Sciences, Tohoku University, Japan
Xiao Zhou
  • Graduate School of Information Sciences, Tohoku University, Japan

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Hiroki Osawa, Akira Suzuki, Takehiro Ito, and Xiao Zhou. Algorithms for Coloring Reconfiguration Under Recolorability Constraints. In 29th International Symposium on Algorithms and Computation (ISAAC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 123, pp. 37:1-37:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


Coloring reconfiguration is one of the most well-studied reconfiguration problems. In the problem, we are given two (vertex-)colorings of a graph using at most k colors, and asked to determine whether there exists a transformation between them by recoloring only a single vertex at a time, while maintaining a k-coloring throughout. It is known that this problem is solvable in linear time for any graph if k <=3, while is PSPACE-complete for a fixed k >= 4. In this paper, we further investigate the problem from the viewpoint of recolorability constraints, which forbid some pairs of colors to be recolored directly. More specifically, the recolorability constraint is given in terms of an undirected graph R such that each node in R corresponds to a color, and each edge in R represents a pair of colors that can be recolored directly. In this paper, we give a linear-time algorithm to solve the problem under such a recolorability constraint if R is of maximum degree at most two. In addition, we show that the minimum number of recoloring steps required for a desired transformation can be computed in linear time for a yes-instance. We note that our results generalize the known positive ones for coloring reconfiguration.

Subject Classification

ACM Subject Classification
  • Mathematics of computing → Graph algorithms
  • combinatorial reconfiguration
  • graph algorithm
  • graph coloring


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