Voronoi diagrams in n · 2o(√lg lg n) time

• Authors: Timothy M. Chan;Mihai Pǎtraşcu
• Venue: Proceedings of the thirty-ninth annual ACM symposium on Theory of computing
• Year: 2007

We reexamine fundamental problems from computational geometry in theallword RAM model, where input coordinates are integers that fit in a machine word. We develop a new algorithm for offline point location, a two-dimensional analog of sorting where one needs to order points with respect to segments. This result implies, for example, that the Voronoi diagram of n points in the plane can be constructed in (randomized) time n· 2O(√ lg lg n). Similar bounds hold for numerous other geometric problems, such as three-dimensional convex hulls, planar Euclidean minimum spanning trees, line segment intersection, and triangulation of non-simple polygons. In FOCS'06, we developed a data structure for online point location, which implied a bound of O(n (lg n)/(lg lg n) for Voronoi diagrams and the other problems. Our current bounds are dramatically better, and a convincing improvement over the classic O(n lg n) algorithms. As in the field of integer sorting, the main challenge is to find ways to manipulate information, while avoiding the online problem (in that case, predecessor search).