Abstract
The ℓ-Coloring problem is the problem to decide whether a graph can be colored with at most ℓ colors. Let P k denote the path on k vertices and G + H and 2H the disjoint union of two graphs G and H or two copies of H, respectively. We solve a known open problem by showing that 3-Coloring is polynomial-time solvable for the class of graphs with no induced 2P 3. This implies that the complexity of 3-Coloring for graphs with no induced graph H is now classified for any fixed graph H on at most 6 vertices. The Vertex Coloring problem is the problem to determine the chromatic number of a graph. We show that Vertex Coloring is polynomial-time solvable for the class of triangle-free graphs with no induced 2P 3 and for the class of triangle-free graphs with no induced P 2 + P 4. This solves two open problems of Dabrowski, Lozin, Raman and Ries and implies that the complexity of Vertex Coloring for triangle-free graphs with no induced graph H is now classified for any fixed graph H on at most 6 vertices. Our proof technique for the case H = 2P 3 is based on a novel structural result on the existence of small dominating sets in 2P 3-free graphs that admit a k-coloring for some fixed k.
This work has been supported by EPSRC (EP/G043434/1).
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Broersma, H., Golovach, P.A., Paulusma, D., Song, J. (2010). On Coloring Graphs without Induced Forests. In: Cheong, O., Chwa, KY., Park, K. (eds) Algorithms and Computation. ISAAC 2010. Lecture Notes in Computer Science, vol 6507. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-17514-5_14
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