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Improved Approximation of Two Watchmen's Routes in Simple Polygons
Malmö University, Faculty of Technology and Society (TS), Department of Computer Science and Media Technology (DVMT).ORCID iD: 0000-0002-2161-6571
Malmö University, Faculty of Technology and Society (TS), Department of Computer Science and Media Technology (DVMT).ORCID iD: 0000-0002-1342-8618
Department of Science and Technology, Linköping University, Sweden.ORCID iD: 0000-0003-2548-5756
2026 (English)In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2026, Vol. 370, article id 11Conference paper, Published paper (Refereed)
Abstract [en]

We study the watchman route problem for a set of two watchmen for the objective of minimizing the length of the longest route (min-max) inside a simple polygon P having n vertices, which is known to be weakly NP-hard. First, we consider seeing a discrete set of m points in the interior of P. We show that even this problem is weakly NP-hard and present an approximation algorithm with approximation ratio 2 + ε that runs in O(m5n) time, assuming that a starting point for each of the two routes is given. We generalize the algorithm to see all of the interior of P in O(n6) time with approximation ratio 2 + π/2 ≈ 3.571, improving on the previously known best algorithm that has an approximation ratio of ≈ 6.922 and runtime O(n2) [8]. Finally, we describe how to extend this algorithm to the case where no starting points are given, this taking O(n8) time, yielding an approximation ratio of 3 + π/2 ≈ 4.571, improving on the previously known best approximation algorithm with ratio ≈ 5.969 also having runtime O(n8) [8].

Place, publisher, year, edition, pages
Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2026. Vol. 370, article id 11
Keywords [en]
Art gallery problem, multiple watchmen, path planning, polygons, watchman route problem
National Category
Computer Sciences
Identifiers
URN: urn:nbn:se:mau:diva-87214DOI: 10.4230/LIPIcs.SWAT.2026.11Scopus ID: 2-s2.0-105042436969ISBN: 9783959774215 (electronic)OAI: oai:DiVA.org:mau-87214DiVA, id: diva2:2087770
Conference
20th Scandinavian Symposium on Algorithm Theory, SWAT 2026, 17-19 Jun 2026, Copenhagen, Denmark
Funder
Swedish Research CouncilSwedish Research Council, 2021-03810Available from: 2026-07-22 Created: 2026-07-22 Last updated: 2026-07-24Bibliographically approved

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Brötzner, AnnaNilsson, Bengt J.Schmidt, Christiane
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