The Rabin-Karp algorithm is a string matching/searching algorithm developed by Michael O. Rabin and Richard M. Karp. It uses hashing technique and brute force for comparison, and is a good candidate for plagiarism detection.
- 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 until characters that don't match are found.
How the Rabin-Karp Algorithm Works
- Calculate hash value of pattern
- Calculate hash value of first M characters of text
- Compare both hash values
- If they are unequal, calculate hash value for next M characters of text and compare again.
- 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.