wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (04/19/89)
Approximate String Matching". DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES DATA STRUCTURING SEMINAR -Monday, April 24, 1989 Mr. Esko Ukonnen of University of Helsinki will speak on "Efficient Approximate String Matching". TIME: 3:30 PM ROOM: DC 1302 ABSTRACT We discuss recent advances in sequential algorithms for computing the edit distance between two strings and for finding approximate occurrences of a string (the pattern) in another string (the text). Such algorithms can be based on a very simple dynamic programming method with running time O(mn) where m and n are the lengths of the two strings compared. The emphasis of the talk is on different ideas of speeding up the basic dynamic programming. The resulting algorithms include a method for the edit distance problem with the desirable property of being the faster the smaller is the actual distance. For the approximate string pattern matching problem we obtain various O(kn) methods where n is the length of the text and k is the maximum distance allowed in a match.
wlrush@water.waterloo.edu (Wenchantress Wench Wendall) (07/06/89)
will speak on ``Priority Search Trees: Applications and Variations.'' DEPARTMENT OF COMPUTER SCIENCE UNIVERSITY OF WATERLOO SEMINAR ACTIVITIES DATA STRUCTURING SEMINAR -Monday, July 10, 1989 Professor Dr. Thomas Ottman, University of Freiburg, will speak on "Priority Search Trees: Applications and Variations." TIME: 3:30 p.m. ROOM: DC 1302 ABSTRACT Priority search trees, invented by McCreight, combine properties of search trees and heaps. They were originally used as a data structure in a time and space optimal algorithm for reporting all pairs of intersecting rectangles in a given set of iso-oriented rectangles in the plane. Possible applications, however, go beyond this special problem. We discuss the dynamic fixed windowing problem as an example. Here insertions and deletions of points are possible and range queries with a translated polygonal window of fixed size. Variants of priority search trees are obtained by choosing an appropriate coordinate system, an underlying class of leaf search trees, the number of points to be stored per node, and the memory (internal or external). We discuss several of these variants, in particular the difficulties in designing appropriate external versions. It turns out that a new class of red-black trees is useful in this context.