Space-efficient algorithms for reachability in directed geometric graphs

The problem of graph Reachability is to decide whether there is a path from one vertex to another in a given graph. In this paper, we study the Reachability problem on three distinct graph families - intersection graphs of Jordan regions, unit contact disk graphs (penny graphs), and chordal graphs....

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Bibliographic Details
Published in:Theoretical computer science Vol. 961; p. 113938
Main Authors: Bhore, Sujoy, Jain, Rahul
Format: Journal Article
Language:English
Published: Elsevier B.V 15.06.2023
Subjects:
Geometric intersection graphs
Reachability
Space-efficient algorithms
Geometric intersection graphs
Space-efficient algorithms
Reachability
ISSN:0304-3975, 1879-2294
Online Access:Get full text
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Summary:The problem of graph Reachability is to decide whether there is a path from one vertex to another in a given graph. In this paper, we study the Reachability problem on three distinct graph families - intersection graphs of Jordan regions, unit contact disk graphs (penny graphs), and chordal graphs. For each of these graph families, we present space-efficient algorithms for the Reachability problem. For intersection graphs of Jordan regions, we show how to obtain a “good” vertex separator in a space-efficient manner and use it to solve the Reachability in polynomial time and O(m1/2log⁡n) space, where n is the number of Jordan regions, and m is the total number of crossings among the regions. We use a similar approach for chordal graphs and obtain a polynomial time and O(m1/2log⁡n) space algorithm, where n and m are the number of vertices and edges, respectively. However, for unit contact disk graphs (penny graphs), we use a more involved technique and obtain a better algorithm. We show that for every ϵ>0, there exists a polynomial time algorithm that can solve Reachability in an n vertex directed penny graph, using O(n1/4+ϵ) space. We note that the method used to solve penny graphs does not extend naturally to the class of geometric intersection graphs that include arbitrary size cliques.
ISSN:0304-3975
1879-2294
DOI:10.1016/j.tcs.2023.113938