Creative Commons Attribution 3.0 Unported license
We resolve an open problem due to Tetsuo Asano, showing how to compute the shortest path in a polygon, given in a read only memory, using sublinear space and subquadratic time. Specifically, given a simple polygon P with n vertices in a read only memory, and additional working memory of size m, the new algorithm computes the shortest path (in P) in O(n^2 / m) expected time, assuming m = O(n / log^2 n). This requires several new tools, which we believe to be of independent interest. Specifically, we show that violator space problems, an abstraction of low dimensional linear-programming (and LP-type problems), can be solved using constant space and expected linear time, by modifying Seidel's linear programming algorithm and using pseudo-random sequences.
@InProceedings{harpeled:LIPIcs.SOCG.2015.111,
author = {Har-Peled, Sariel},
title = {{Shortest Path in a Polygon using Sublinear Space}},
booktitle = {31st International Symposium on Computational Geometry (SoCG 2015)},
pages = {111--125},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-939897-83-5},
ISSN = {1868-8969},
year = {2015},
volume = {34},
editor = {Arge, Lars and Pach, J\'{a}nos},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SOCG.2015.111},
URN = {urn:nbn:de:0030-drops-50941},
doi = {10.4230/LIPIcs.SOCG.2015.111},
annote = {Keywords: Shortest path, violator spaces, limited space}
}