freeCodeCamp/guide/english/algorithms/string-matching-algorithms/rabin-karp-algorithm/index.md

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Rabin Karp Algorithm

Rabin-Karp Algorithm

• A string matching/searching algorithm developed by Michael O. Rabin and Richard M. Karp.
• Uses hashing technique and brute force for comparison.

Important terms

• pattern is the string to be searched. Consider length of pattern as M characters.
• text is the whole text from which the pattern is to be searched. Consider length of text as N characters.

What is brute force comparison?

In brute force comparison each character of pattern is compared with each character of text untill unmatching characters are found.

Working of Rabin-Karp Algorithm

1. Calculate hash value of pattern
2. Calculate hash value of first M characters of text
3. Compare both hash values
4. If they are unequal, calculate hash value for next M characters of text and compare again.
5. If they are equal, perform a brute force comparison.

hash_p = hash value of pattern
hash_t = hash value of first M letters in body of text
do
	if (hash_p == hash_t) 
		brute force comparison of pattern and selected section of text
	hash_t= hash value of next section of text, one character over
while (end of text or brute force comparison == true)

Advantage over Naive String Matching Algorithm

This technique results in only one comparison per text sub-sequence and brute force is only required when the hash values match.

Applications

• Plagiarism Detection

More Information:

Rabin-Karp on Wikipedia