Rabin-Karp's Algorithm

A Complete Guide to the Rabin-Karp Algorithm

A hash function is used by the Rabin-Karp algorithm, a string-searching technique, to more effectively search for substrings inside a longer string. As it requires fewer comparisons to discover a match than the conventional method of comparing each sub-string with the pattern, this technique is a significant improvement. We'll get into the specifics of the Rabin-Karp algorithm's operation, implementation, and advantages over alternative string-searching algorithms in this post.

What is the Rabin-Karp Algorithm?

The Rabin-Karp algorithm is a string-searching formula that compares substrings to a given pattern using a hash function.

The algorithm's premise is that comparing two hash values rather than two substrings is quicker. It is clear that the sub-strings are not equal if the hash values are not equal, and it is likely that they are equal if the hash values are equal, but more comparison is required to be sure.

How does the Rabin-Karp Algorithm work?

In the beginning of the Rabin-Karp algorithm, a very big prime number, p, and a random number, x, between 1 and p-1, are chosen.

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The random number is used to select the specific hash function, while the prime number is used to select a random polynomial hash function from the family. The pattern's hash value and the hash values of all the text's substrings are calculated using the polynomial hash function. The algorithm then compares the hash values for each of the text's sub-strings. The algorithm advances to the subsequent sub-string if the hash values are not identical.

The approach uses the AreEqual function to determine whether the sub-strings are equal if the hash values are equal. The location of the sub-string is added to the list of positions if the sub-strings are equal, and the algorithm moves on to the following sub-string.

Rabin-Karp algorithm implementation

The Rabin-Karp algorithm is basic to use and has a clear flow. Choosing a huge prime number, p, and a random number, x, between 1 and p-1, is the first stage. The pattern's polynomial hash, which won't alter throughout the method, is computed next. The algorithm then iterates through the text's sub-strings, computing each one's hash value using the PolyHash technique. The method moves on to the next sub-string if the hash values of the pattern and the sub-string do not match. The approach uses the AreEqual function to determine whether the sub-strings are equal if the hash values are equal. The method moves on to the next sub-string if the sub-strings are equal, at which point the position of the sub-string is added to the list of positions.

Advantages of the Rabin-Karp Algorithm

Compared to other string-searching algorithms, the Rabin-Karp algorithm has a number of benefits. First off, it performs more quickly than the conventional method of comparing each sub-string to the pattern. Furthermore, because the likelihood of a false alert is proportional to the length of the pattern over the huge prime number p, it is extremely unlikely. Thirdly, because the technique is simple to use, it is a fantastic option for beginners who are just learning about string-searching algorithms.