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Separator Theorem and Algorithms for Planar Hyperbolic Graphs

Authors Sándor Kisfaludi-Bak, Jana Masaříková, Erik Jan van Leeuwen, Bartosz Walczak, Karol Węgrzycki

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Author Details

Sándor Kisfaludi-Bak
  • Department of Computer Science, Aalto University, Espoo, Finland
Jana Masaříková
  • Institute of Informatics, University of Warsaw, Poland
Erik Jan van Leeuwen
  • Department of Information and Computing Sciences, Utrecht University, The Netherlands
Bartosz Walczak
  • Department of Theoretical Computer Science, Faculty of Mathematics and Computer Science, Jagiellonian University, Kraków, Poland
Karol Węgrzycki
  • Saarland University, Saarbrücken, Germany
  • Max Planck Institute for Informatics, Saarbrücken, Germany

Funding

  • Walczak, Bartosz: Partially supported by the National Science Center of Poland under grant No. 2019/34/E/ST6/00443.
  • Węgrzycki, Karol: This work is part of the project TIPEA that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 850979).

Acknowledgements

This research was partially carried out during the Parameterized Algorithms Retreat of the University of Warsaw, PARUW 2022, held in Będlewo in April 2022.

Cite AsGet BibTex

Sándor Kisfaludi-Bak, Jana Masaříková, Erik Jan van Leeuwen, Bartosz Walczak, and Karol Węgrzycki. Separator Theorem and Algorithms for Planar Hyperbolic Graphs. In 40th International Symposium on Computational Geometry (SoCG 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 293, pp. 67:1-67:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
https://doi.org/10.4230/LIPIcs.SoCG.2024.67

Abstract

The hyperbolicity of a graph, informally, measures how close a graph is (metrically) to a tree. Hence, it is intuitively similar to treewidth, but the measures are formally incomparable. Motivated by the broad study of algorithms and separators on planar graphs and their relation to treewidth, we initiate the study of planar graphs of bounded hyperbolicity. Our main technical contribution is a novel balanced separator theorem for planar δ-hyperbolic graphs that is substantially stronger than the classic planar separator theorem. For any fixed δ ⩾ 0, we can find a small balanced separator that induces either a single geodesic (shortest) path or a single geodesic cycle in the graph. An important advantage of our separator is that the union of our separator (vertex set Z) with any subset of the connected components of G - Z induces again a planar δ-hyperbolic graph, which would not be guaranteed with an arbitrary separator. Our construction runs in near-linear time and guarantees that the size of the separator is poly(δ) ⋅ log n. As an application of our separator theorem and its strong properties, we obtain two novel approximation schemes on planar δ-hyperbolic graphs. We prove that both Maximum Independent Set and the Traveling Salesperson problem have a near-linear time FPTAS for any constant δ, running in n polylog(n) ⋅ 2^𝒪(δ²) ⋅ ε^{-𝒪(δ)} time. We also show that our approximation scheme for Maximum Independent Set has essentially the best possible running time under the Exponential Time Hypothesis (ETH). This immediately follows from our third contribution: we prove that Maximum Independent Set has no n^{o(δ)}-time algorithm on planar δ-hyperbolic graphs, unless ETH fails.

Subject Classification

ACM Subject Classification
  • Theory of computation → Computational geometry
Keywords
  • Hyperbolic metric
  • Planar Graphs
  • r-Division
  • Approximation Algorithms

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