Abstract
Cops and robber games, introduced by Winkler and Nowakowski (in Discrete Math. 43(2–3), 235–239, 1983) and independently defined by Quilliot (in J. Comb. Theory, Ser. B 38(1), 89–92, 1985), concern a team of cops that must capture a robber moving in a graph. We consider the class of k-chordal graphs, i.e., graphs with no induced (chordless) cycle of length greater than k, k≥3. We prove that k−1 cops are always sufficient to capture a robber in k-chordal graphs. This leads us to our main result, a new structural decomposition for a graph class including k-chordal graphs.
We present a polynomial-time algorithm that, given a graph G and k≥3, either returns an induced cycle larger than k in G, or computes a tree-decomposition of G, each bag of which contains a dominating path with at most k−1 vertices. This allows us to prove that any k-chordal graph with maximum degree Δ has treewidth at most (k−1)(Δ−1)+2, improving the O(Δ(Δ−1)k−3) bound of Bodlaender and Thilikos (Discrete Appl. Math. 79(1–3), 45–61, 1997. Moreover, any graph admitting such a tree-decomposition has small hyperbolicity).
As an application, for any n-vertex graph admitting such a tree-decomposition, we propose a compact routing scheme using routing tables, addresses and headers of size O(klogΔ+logn) bits and achieving an additive stretch of O(klogΔ). As far as we know, this is the first routing scheme with O(klogΔ+logn)-routing tables and small additive stretch for k-chordal graphs.
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Partially supported by programs Fondap and Basal-CMM, Anillo ACT88 and Fondecyt 11090390 (K.S.), FP7 STREP EULER (N.N.), AGAPE, ECOS-SUD, EA. AlDyNet, ANR DISPLEXITY, NCN under contract DEC-2011/02/A/ST6/00201 (A.K.).
This work has been announced at the 39th International Colloquium on Automata, Languages and Programming (ICALP 2012); the extended abstract appeared in the corresponding proceedings [36].
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Kosowski, A., Li, B., Nisse, N. et al. k-Chordal Graphs: From Cops and Robber to Compact Routing via Treewidth. Algorithmica 72, 758–777 (2015). https://doi.org/10.1007/s00453-014-9871-y
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DOI: https://doi.org/10.1007/s00453-014-9871-y