49 lines
1.6 KiB
Markdown
49 lines
1.6 KiB
Markdown
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---
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title: Rabin Karp Algorithm
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---
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## Rabin-Karp Algorithm
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* A string matching/searching algorithm developed by Michael O. Rabin and Richard M. Karp.
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* Uses ***hashing*** technique and ***brute force*** for comparison.
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#### Important terms
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* ***pattern*** is the string to be searched.
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Consider length of pattern as ***M*** characters.
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* ***text*** is the whole text from which the pattern is to be searched.
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Consider length of text as ***N*** characters.
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#### What is brute force comparison?
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In brute force comparison each character of pattern is compared with each character of text untill unmatching characters are found.
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#### Working of Rabin-Karp Algorithm
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1. Calculate hash value of *pattern*
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2. Calculate hash value of first *M* characters of *text*
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3. Compare both hash values
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4. If they are unequal, calculate hash value for next *M* characters of *text* and compare again.
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5. If they are equal, perform a brute force comparison.
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```
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hash_p = hash value of pattern
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hash_t = hash value of first M letters in body of text
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do
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if (hash_p == hash_t)
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brute force comparison of pattern and selected section of text
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hash_t= hash value of next section of text, one character over
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while (end of text or brute force comparison == true)
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```
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#### Advantage over Naive String Matching Algorithm
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This technique results in only one comparison per text sub-sequence and brute force is only required when the hash values match.
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#### Applications
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* ***Plagiarism Detection***
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#### More Information:
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<a href='https://en.wikipedia.org/wiki/Rabin%E2%80%93Karp_algorithm/' target='_blank' rel='nofollow'>Rabin-Karp on Wikipedia</a>
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