arXiv subjects

Simone Faro

Publications and source records attributed to Simone Faro.

22 records · Page 2Linked to original sources

arXiv2010

The Exact String Matching Problem: a Comprehensive Experimental Evaluation

This paper addresses the online exact string matching problem which consists in finding all occurrences of a given pattern p in a text t. It is an extensively studied problem in computer science, mainly due to its direct applications to such diverse areas as text, image and signal processing, speech analysis and recognition, data compression, information retrieval, computational biology and chemistry. Since 1970 more than 80 string matching algorithms have been proposed, and more than 50% of them in the last ten years. In this note we present a comprehensive list of all string matching algorithms and present experimental results in order to compare them from a practical point of view. From our experimental evaluation it turns out that the performance of the algorithms are quite different for different alphabet sizes and pattern length.

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arXiv2010

On Tuning the Bad-Character Rule: the Worst-Character Rule

In this note we present the worst-character rule, an efficient variation of the bad-character heuristic for the exact string matching problem, firstly introduced in the well-known Boyer-Moore algorithm. Our proposed rule selects a position relative to the current shift which yields the largest average advancement, according to the characters distribution in the text. Experimental results show that the worst-character rule achieves very good results especially in the case of long patterns or small alphabets in random texts and in the case of texts in natural languages.

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arXiv2010

String Matching with Inversions and Translocations in Linear Average Time (Most of the Time)

We present an efficient algorithm for finding all approximate occurrences of a given pattern $p$ of length $m$ in a text $t$ of length $n$ allowing for translocations of equal length adjacent factors and inversions of factors. The algorithm is based on an efficient filtering method and has an $\bigO(nm\max(α, β))$-time complexity in the worst case and $\bigO(\max(α, β))$-space complexity, where $α$ and $β$ are respectively the maximum length of the factors involved in any translocation and inversion. Moreover we show that under the assumptions of equiprobability and independence of characters our algorithm has a $\bigO(n)$ average time complexity, whenever $σ= Ω(\log m / \log\log^{1-ε} m)$, where $ε> 0$ and $σ$ is the dimension of the alphabet. Experiments show that the new proposed algorithm achieves very good results in practical cases.

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arXiv2008

Efficient Pattern Matching on Binary Strings

The binary string matching problem consists in finding all the occurrences of a pattern in a text where both strings are built on a binary alphabet. This is an interesting problem in computer science, since binary data are omnipresent in telecom and computer network applications. Moreover the problem finds applications also in the field of image processing and in pattern matching on compressed texts. Recently it has been shown that adaptations of classical exact string matching algorithms are not very efficient on binary data. In this paper we present two efficient algorithms for the problem adapted to completely avoid any reference to bits allowing to process pattern and text byte by byte. Experimental results show that the new algorithms outperform existing solutions in most cases.

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