Tighter bounds on the exact complexity of string matching

Abstract

The paper considers how many character comparisons are needed to find all occurrences of a pattern of length m in a text of length n. The main contribution is to show an upper bound of the form n + O(n/m) character comparisons, following preprocessing. Specifically, the authors show an upper bound of n+8/3(m+1)(n-m) character comparisons. This bound is achieved by an online algorithm which performs O(n) work in total, requires O(m) space and O(m/sup 2/) time for preprocessing. In addition the following lower bounds are shown: for online algorithms, a bound of n+11/5(m+1) (n-m) character comparisons for m = 10 + 11 k, for any integer k >or= 1, and for general algorithms, a bound of n+2(n-m)/m+3 character comparisons, for m=2 k+l, for any integer k>or=1.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>