Hashing

Hashing is a technique used in data structures to map data of arbitrary size to fixed-size values, typically for the purpose of creating a faster and more efficient data retrieval system. The concept is based on a hash function, which takes an input (or 'key') and produces a fixed-size string of characters, which is usually a hash code. The hash code is then used to index into a data structure (usually an array or a hash table) where the values are stored.

Let's go through the key components and concepts related to hashing:

Hash Function:

A hash function is a mathematical function that takes an input (or 'key') and produces a fixed-size string of characters, which is the hash code. The goal is to distribute the keys uniformly across the range of possible hash codes.

Key properties of a good hash function:

  1. Deterministic: For the same input, the hash function should always produce the same hash code.
  2. Efficient: The hash function should be computationally efficient to calculate.
  3. Uniform Distribution: The hash function should distribute keys as uniformly as possible across the hash code space to minimize collisions.

Hash Code:

The output of the hash function is called the hash code. It is used as an index to access the corresponding data in the data structure.

Collision:

A collision occurs when two different keys hash to the same hash code. Collisions are inevitable due to the finite range of hash codes and the potentially infinite number of keys. Handling collisions is a crucial aspect of designing a good hashing system.

Collision Resolution Techniques:

  1. Open Addressing: In open addressing, when a collision occurs, the algorithm looks for the next available slot in the hash table. This can be done using various methods such as linear probing, quadratic probing, or double hashing.

  2. Separate Chaining: In separate chaining, each slot in the hash table contains a linked list. When a collision occurs, the new key is simply appended to the linked list at that slot.

Applications of Hashing:

  1. Data Retrieval: Hashing is used in data structures like hash tables, where it provides constant time average-case complexity for search, insert, and delete operations.

  2. Cryptography: Hash functions are used in various cryptographic applications, such as digital signatures and checksums.

  3. Load Balancing: Hashing can be used in load balancing algorithms to distribute data or tasks evenly across multiple nodes or servers.

  4. Caching: Hash functions are used in caching mechanisms to quickly locate cached data.

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