Speeding Up Two String-Matching Algorithms

We show how to speed up two string-matching algorithms: the Boyer-Moore algorithm (BM algorithm), and its version called here the reverse factor algorithm (RF algorithm). The RF algorithm is based on factor graphs for the reverse of the pattern.The main feature of both algorithms is that they scan the text right-to-left from the supposed right position of the pattern. The BM algorithm goes as far as the scanned segment (factor) is a suffix of the pattern. The RF algorithm scans while the segment is a factor of the pattern. Both algorithms make a shift of the pattern, forget the history, and start again. The RF algorithm usually makes bigger shifts than BM, but is quadratic in the worst case. We show that it is enough to remember the last matched segment (represented by two pointers to the text) to speed up the RF algorithm considerably (to make a linear number of inspections of text symbols, with small coefficient), and to speed up the BM algorithm (to make at most 2.n comparisons). On...

• Type: Conference
• Year: 1992
• Where: STACS
• Authors: Maxime Crochemore, Thierry Lecroq, Artur Czumaj, Leszek Gasieniec, Stefan Jarominek, Wojciech Plandowski, Wojciech Rytter
• Keywords: BM Algorithm, Reverse Factor Algorithm, RF Algorithm, STACS 1992, Theoretical Computer Science