In this paper we study the all-pairs shortest paths problem in (unweighted) unit-disk graphs. The previous best solution for this problem required O(n^2 log n) time, by running the O(n log n)-time single-source shortest path algorithm of Cabello and Jejcic [Comput. Geom., 2015] from every source vertex,where n is the number of vertices. We not only manage to eliminate the logarithmic factor, but also obtain the first (slightly) subquadratic algorithm for the problem, running in O(n^2 sqrt{ frac{log log n}{log n} }) time. Our algorithm computes an implicit representation of all the shortest paths, and, in the same amount of time, can also compute the diameter of the graph.
@InProceedings{chan_et_al:LIPIcs.ISAAC.2016.24, author = {Chan, Timothy M. and Skrepetos, Dimitrios}, title = {{All-Pairs Shortest Paths in Unit-Disk Graphs in Slightly Subquadratic Time}}, booktitle = {27th International Symposium on Algorithms and Computation (ISAAC 2016)}, pages = {24:1--24:13}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-026-2}, ISSN = {1868-8969}, year = {2016}, volume = {64}, editor = {Hong, Seok-Hee}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2016.24}, URN = {urn:nbn:de:0030-drops-67948}, doi = {10.4230/LIPIcs.ISAAC.2016.24}, annote = {Keywords: unit-disk graphs, all-pairs shortest paths, computational geometry} }
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