Performance Analysis of Selected String Matching Algorithms based on Good Suffix and Bad Character Rule

Abstract

String matching is a problem where a pattern is to be searched within a text. In this paper, we study about selected string matching algorithms which compute shifts; based on good suffix rule and/or bad character rule or their variations. Algorithms are compared on the basis of their execution time for different data sets; those differ on patterns and alphabet sizes. Finally, we present a summary for the selection of these algorithms in different applications, based on the experimental results obtained. Good Suffix:Rule says if a mismatch occurs between the character 'a' of the pattern X and the character 'b' of the text Y during an attempt at position 'j' in Y. Then the already matched set of characters is considered as a suffix. The good-suffix shift consists in aligning this suffix with its rightmost occurrence in X that is preceded by a character different from character at position j. If there exists no such segment, the shift consists in aligning the longest set of characters in the suffix in Y with a matching prefix of X. Else shift the pattern ahead of suffix. Bad character:The bad-character shift consists in aligning the mismatched text character 'b' in Y with its rightmost occurrence in X. If 'b' does not occur in the pattern X, no occurrence of X in Y can include 'b', then the left end of the window is aligned with the character immediately after b. Selected Algorithms Boyer Moore Algorithm [1][2]:The algorithm scans the characters of the pattern from right to left beginning with the rightmost one. In case of a mismatch (or a complete match of the whole pattern) it uses two precomputed functions to shift the window to the right. These two shift functions are called the good-suffix shift (also called matching shift and the badcharacter shift (also called the occurrence shift). Maximum of the two rules is taken and patterns is shifted accordingly. Turbo Boyer Moore [3]: The Turbo-BM algorithm is an amelioration of the Boyer-Moore algorithm. It needs no extra preprocessing and requires only a constant extra space with respect to the original Boyer-Moore algorithm. It improves the worst-case complexity of Boyer-Moore algorithm. Zhu Takoaka [4]: Zhu and Takaoka designed an algorithm which performs the shift by considering the bad-character shift for two consecutive text characters. It simply modifies the Bad character rule employed in Boyer Moore, to consider two characters in case of mismatch.