Apostolico–Giancarlo algorithm: Difference between revisions

Revision as of 02:32, 5 December 2011

Revision as of 17:45, 2 April 2012

Line 1:

{{context|date=December 2011}}

{{Lead rewrite|date=September 2009}}

In [[computer science]], the '''Apostolico–Giancarlo algorithm''' is a variant of the [[Boyer-Moore string search algorithm]], the basic application of which is searching for occurrences of a pattern <math>P</math> in a text <math>T</math>. As with other comparison-based string searches, this is done by aligning <math>P</math> to a certain index of <math>T</math> and checking whether a match occurs at that index. <math>P</math> is then shifted relative to <math>T</math> according to the rules of the Boyer-Moore algorithm, and the process repeats until the end of <math>T</math> has been reached. Application of the Boyer-Moore shift rules often results in large chunks of the text being skipped entirely.

In [[computer science]], the '''Apostolico–Giancarlo algorithm''' is an algorithm which remembers the length of the longest suffix of the pattern ending at the right position of the window at the end of each attempt. These information are stored in a table skip. It was designed by Alberto Apostolico and Raffaele Giancarlo.

With regard to the shift operation, Apostolico-Giancarlo is exactly equivalent in functionality to Boyer-Moore. The utility of Apostolico-Giancarlo is to speed up the match-checking operation at any index. With Boyer-Moore, finding an occurrence of <math>P</math> in <math>T</math> requires that all <math>n</math> characters of <math>P</math> be explicitly matched. For certain patterns and texts, this is very inefficient - a simple example is when both pattern and text consist of the same repeated character, in which case Boyer-Moore runs in <math>O(n m)</math> where <math>m</math> is the length in characters of <math>T</math>.

==References==