# Rabin-Karp Algorithm (String Matching Algo)

## 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

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