Hashing is a technique used in computer science to efficiently store and retrieve data. It involves converting an input (such as a string or an integer) into a fixed-size output, known as a hash code or hash value, using a mathematical function called a hash function. This hash value is then used as an index to store the actual data in a data structure called a hash table.
Key Concepts of Hashing
Hash Function:
A hash function takes an input (or 'key') and returns a fixed-size string of bytes. The output is typically a numerical value that serves as an index in a hash table.
The function must be deterministic, meaning it should always produce the same output for the same input.
A good hash function distributes keys uniformly across the hash table to minimize collisions.
Hash Table:
A hash table is a data structure that stores key-value pairs. The key is processed by the hash function to generate an index, which determines where the value is stored.
This allows for fast data retrieval, as the hash value directly points to the location of the data.
Collisions:
Collisions occur when two different keys produce the same hash value. This is an inevitable aspect of hashing due to the finite size of the hash table.
Common collision resolution techniques include:
Chaining: Storing multiple elements at the same index using a linked list.
Open Addressing: Finding another open slot within the hash table through methods like linear probing, quadratic probing, or double hashing.
Applications of Hashing
Data Retrieval: Hashing allows for quick access to data, making it ideal for applications like database indexing and caching.
Data Integrity: Hash functions are used in checksums and digital signatures to verify data integrity.
Cryptography: Cryptographic hash functions (e.g., SHA-256) are used to secure data by generating unique hash values that are difficult to reverse-engineer.
