Inplace convex hull of a polygonal line in linear time

• Version to appear in CGTA
• Version LATIN'04
• Slides of the presentation

Abstract: We present space-efficient algorithms for computing the convex hull of a simple polygonal line in-place, in linear time. It turns out that the problem is as hard as stable partition, i.e., if there were a truly simple solution then stable partition would also have a truly simple solution, and vice versa. Nevertheless, we present a simple self-contained solution that uses O(log n) space, and indicate how to improve it to O(1) space with the same techniques used for stable partition. If the points inside the convex hull can be discarded, then there is a truly simple solution that uses a single call to stable partition, and even that call can be spared if only extreme points are desired (and not their order). If the polygonal line is closed, then the problem admits a very simple solution which does not call for stable partitioning at all.

Related publications

• Space-efficient planar convex hull algorithms, with J. Iacono, J. Katajainen, P. Morin, J. Morrison, and G. Toussaint.
• Towards in-place geometric algorithms and data structures, with T. Chan, and E. Chen.