ON MAINTAINING THE WIDTH AND DIAMETER OF A PLANAR POINT-SET ONLINE
Efficient online algorithms are presented for maintaining the (almost-exact) width and diameter of a dynamic planar point-set, S. Let n be the number of points currently in S, let W and D denote the width and diameter of S, respectively, and let α>1 and β≥1 be positive, integer-valued parameters. The algorithm for the width problem uses O(αn) space, supports updates in O(α log 2 n) time, and reports in O(α log 2 n) time an approximation, Ŵ, to the width such that [Formula: see text]. The algorithm for the diameter problem uses O(βn) space, supports updates in O(β log n) time, and reports in O(β) time an approximation, [Formula: see text], to the diameter such that [Formula: see text]. Thus, for instance, even for α as small as 11, Ŵ/W≤1.01, and for β as small as 9, [Formula: see text]. All bounds stated are worst-case. Both algorithms, but especially the one for the diameter problem, use well-understood data structures and should be simple to implement. The diameter result yields a fast implementation of the greedy heuristic for maximum-weight Euclidean matching and an efficient online algorithm to maintain approximate convex hulls in the plane.