2026-07-23T16:35:29Z https://drops.dagstuhl.de/oai

oai:drops-oai.dagstuhl.de:7197 2024-03-06T10:39:57Z ddc:004 open_access

Exact Algorithms for Terrain Guarding Ashok, Pradeesha Fomin, Fedor V. Kolay, Sudeshna Saurabh, Saket Zehavi, Meirav Terrain Guarding Art Gallery Exponential-Time Algorithms Given a 1.5-dimensional terrain T, also known as an x-monotone polygonal chain, the Terrain Guarding problem seeks a set of points of minimum size on T that guards all of the points on T. Here, we say that a point p guards a point q if no point of the line segment pq is strictly below T. The Terrain Guarding problem has been extensively studied for over 20 years. In 2005 it was already established that this problem admits a constant-factor approximation algorithm [SODA 2005]. However, only in 2010 King and Krohn [SODA 2010] finally showed that Terrain Guarding is NP-hard. In spite of the remarkable developments in approximation algorithms for Terrain Guarding, next to nothing is known about its parameterized complexity. In particular, the most intriguing open questions in this direction ask whether it admits a subexponential-time algorithm and whether it is fixed-parameter tractable. In this paper, we answer the first question affirmatively by developing an n^O(sqrt{k})-time algorithm for both Discrete Terrain Guarding and Continuous Terrain Guarding. We also make non-trivial progress with respect to the second question: we show that Discrete Orthogonal Terrain Guarding, a well-studied special case of Terrain Guarding, is fixed-parameter tractable. Schloss Dagstuhl – Leibniz-Zentrum für Informatik Pradeesha Ashok and Fedor V. Fomin and Sudeshna Kolay and Saket Saurabh and Meirav Zehavi 2017 Is Part Of LIPIcs, Volume 77, 33rd International Symposium on Computational Geometry (SoCG 2017) InProceedings Text doc-type:ResearchArticle publishedVersion application/pdf doi:10.4230/LIPIcs.SoCG.2017.11 urn:nbn:de:0030-drops-71975 https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2017.11 eng https://creativecommons.org/licenses/by/3.0/legalcode