String Hashing (Rolling Hash) 🎯

Welcome to an exciting journey through String Hashing, a powerful technique used in Computer Science! In this lesson, we'll learn about Rolling Hash, a variant of string hashing that's especially useful for processing large amounts of data. 📝

Why String Hashing? 💡

String Hashing is a method of converting strings into numbers (hashes) for efficient data processing. It helps in solving problems like pattern matching, frequency counting, and string compression.

What is Rolling Hash? 💡

Rolling Hash is a type of string hashing where the hash value of a string is updated incrementally as we move through the string. This is particularly useful when we need to find patterns within a large amount of data.

Understanding the Basics 📝

Hash Function A hash function is a mathematical operation that transforms a string into a fixed-length numerical value (hash).
Collision When two different strings produce the same hash value, we have a collision. To handle collisions, we can use techniques like chaining or open addressing.
Rolling Hash Function A rolling hash function updates the hash value incrementally as we move through the string. It's computed as:

python
hash(s[i]) = (hash(s[i-1]) * P + s[i]) % M

Here, P and M are constants called the modulus and prime modulus respectively.

Implementing Rolling Hash 💡

Here's a simple Python example of a rolling hash function:

python

def rolling_hash(s, P=256, M=1000000007):
    hash_value = 0
    for i in range(len(s)):
        hash_value = (hash_value * P + ord(s[i])) % M
    return hash_value

In this code, ord() is a built-in Python function that returns the Unicode code point of a character.

Practical Applications 🎯

Text Indexing Rolling hash can be used to create efficient data structures for full-text indexing in databases.
Pattern Matching Rolling hash can help us find patterns within large amounts of data quickly.

Quiz Time 💡

Stay tuned for more advanced examples and applications of Rolling Hash in the world of Computer Science! 🎯