Stabbing Pairwise Intersecting Disks by Five Points

Authors Sariel Har-Peled , Haim Kaplan, Wolfgang Mulzer , Liam Roditty, Paul Seiferth, Micha Sharir, Max Willert

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Author Details

Sariel Har-Peled
  • Department of Computer Science, University of Illinois, Urbana, IL 61801, USA
Haim Kaplan
  • School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel
Wolfgang Mulzer
  • Institut für Informatik, Freie Universität Berlin, 14195 Berlin, Germany
Liam Roditty
  • Department of Computer Science, Bar Ilan University, Ramat Gan 5290002, Israel
Paul Seiferth
  • Institut für Informatik, Freie Universität Berlin, 14195 Berlin, Germany
Micha Sharir
  • School of Computer Science, Tel Aviv University, Tel Aviv 69978, Israel
Max Willert
  • Institut für Informatik, Freie Universität Berlin, 14195 Berlin, Germany

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Sariel Har-Peled, Haim Kaplan, Wolfgang Mulzer, Liam Roditty, Paul Seiferth, Micha Sharir, and Max Willert. Stabbing Pairwise Intersecting Disks by Five Points. In 29th International Symposium on Algorithms and Computation (ISAAC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 123, pp. 50:1-50:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)


Suppose we are given a set D of n pairwise intersecting disks in the plane. A planar point set P stabs D if and only if each disk in D contains at least one point from P. We present a deterministic algorithm that takes O(n) time to find five points that stab D. Furthermore, we give a simple example of 13 pairwise intersecting disks that cannot be stabbed by three points. This provides a simple - albeit slightly weaker - algorithmic version of a classical result by Danzer that such a set D can always be stabbed by four points.

Subject Classification

ACM Subject Classification
  • Mathematics of computing → Combinatorics
  • Disk graph
  • piercing set
  • LP-type problem


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