Data Structures and Algorithms

# What is Rabin-Karp Algorithm and How Does it Work?

In this article, I will explain What is Rabin-Karp Algorithm and How Does it Work.

The Rabin-Karp algorithm is a string matching algorithm that uses hashing to find all occurrences of a pattern string in a text string. The algorithm works by computing a hash value for the pattern string and for all substrings of the text string with the same length as the pattern string. It then compares the hash values to determine if there is a match.

The hash function used in Rabin-Karp algorithm is a rolling hash function, which means that the hash value of a substring is computed by reusing the hash value of the previous substring. This allows the algorithm to compute the hash values of all substrings of the text string with the same length as the pattern string in O(n) time, where n is the length of the text string.

In order to avoid spurious hits caused by hash collisions, the Rabin-Karp algorithm uses a technique called the “Monte Carlo method” to verify the matches. It checks whether the hash value of the pattern string matches the hash value of a substring of the text string, and if it does, it verifies that the pattern string actually matches the substring by comparing them character by character.

The time complexity of the Rabin-Karp algorithm is O(n+m), where n is the length of the text string and m is the length of the pattern string. The Rabin-Karp algorithm is efficient for finding multiple occurrences of a pattern in a long text string, and it can be further optimized by using a more advanced hash function and other techniques such as preprocessing the pattern string.

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