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A basic example of string searching is when the pattern and the searched text are arrays of elements of an alphabet Σ. Σ may be a human language alphabet, for example, the letters A through Z and other applications may use a binary alphabet (Σ = {0,1}) or a DNA alphabet (Σ = {A,C,G,T}) in bioinformatics.
clear(S): delete all elements of S. equal(S 1 ', S 2 '): checks whether the two given sets are equal (i.e. contain all and only the same elements). hash(S): returns a hash value for the static set S such that if equal(S 1, S 2) then hash(S 1) = hash(S 2) Other operations can be defined for sets with elements of a special type:
The longest common substrings of a set of strings can be found by building a generalized suffix tree for the strings, and then finding the deepest internal nodes which have leaf nodes from all the strings in the subtree below it. The figure on the right is the suffix tree for the strings "ABAB", "BABA" and "ABBA", padded with unique string ...
Then if P is shifted to k 2 such that its left end is between c and k 1, in the next comparison phase a prefix of P must match the substring T[(k 2 - n)..k 1]. Thus if the comparisons get down to position k 1 of T , an occurrence of P can be recorded without explicitly comparing past k 1 .
String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly.
This is the set of all strings that can be made by concatenating any finite number (including zero) of strings from the set described by R. For example, if R denotes {"0", "1"}, (R*) denotes the set of all finite binary strings (including the empty string).
A left identity element that is also a right identity element if called an identity element. The empty set is an identity element of binary union and symmetric difference , and it is also a right identity element of set subtraction :
In computer science, the Knuth–Morris–Pratt algorithm (or KMP algorithm) is a string-searching algorithm that searches for occurrences of a "word" W within a main "text string" S by employing the observation that when a mismatch occurs, the word itself embodies sufficient information to determine where the next match could begin, thus bypassing re-examination of previously matched characters.