Showing papers by "Costas S. Iliopoulos published in 1998"

On-line algorithms for k-Covering

Abstract: An O(n2(n-k)) on-line algorithm for computing a minimum set of k-covers for a given string of length n is presented. A straightforward modification of the algorithms yields O(kn2(n-k)) algorithms for computing a minimum set of k-covers and k-segments for a given circular string of length n. We show further that the number of such minimum sets of k-covers may be exponential. Similar time complexity bounds hold for computing the minimum sets of k-segments and k-seeds.

Two-Dimensional Prefix String Matching and Covering on Square Matrices

Abstract: Two linear time algorithms are presented. One for determining, for every position in a given square matrix, the longest prefix of a given pattern (also a square matrix) that occurs at that position and one for computing all square covers of a given two-dimensional square matrix.

Algorithms for computing evolutionary chains in molecular and musical sequences

Abstract: Musical patterns that recur in approximate, rather than identical, form within the body of a musical work are considered to be of considerable importance in music analysis Here we consider the "evolutionary chain problem": this is the problem of computing a chain of all "motif" recurrences, each of which is a transformation of ("similar" to) the original motif, but each of which may be progressively further from the original Here we consider several variants of the evolutionary chain problem and we present e cient algorithms and implementations for solving them

The covers of a circular Fibonacci string

Abstract: Fibonacci strings turn out to constitute worst cases for a number of computer algorithms which find generic patterns in strings. Examples of such patterns are repetitions, Abelian squares, and "covers". In particular, we characterize in this paper the covers of a circular Fibonacci string C(F k ) and show that they are \Theta(jF k j 2 ) in number. We show also that, by making use of an appropriate encoding, these covers can be reported in \Theta(jF k j) time. By contrast, the fastest known algorithm for computing the covers of an arbitrary circular string of length n requires time O(n log n).

Validating and Decomposing Partially Occluded Two-Dimensional Images (Extended Abstract).

Abstract: A partially occluded scene in an image consists of a number of objects that are partially obstructed by others. Validating a partially occluded image consists of generating a sequence of concatenated and possibly overlapping objects that corresponds to the input image. The algorithm presented here validates a two-dimensional image X of size r s over a set of k objects of identical size m m in O(mrs) time.

Massively Parallel Suffix Array Construction

Abstract: This paper considers the construction of the suffix array of a string on the MasPar MP-2 architecture. suffix arrays are space-efficient variants of the suffix trees, a fundamental dictionary data structure that is the backbone of many string algorithms for pattern matching and textual information retreival. We adapt known PRAM techniques for implementation on the MasPar: bulletin boards, doubling techniques and sorting methods. Performance results are presented.