Hash tables are a fundamental data structure used in computer science. They provide fast access to data by using a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.

What is a Hash Table?

A hash table is a data structure that implements an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.

Key Features of Hash Tables

  • Fast Access: Hash tables provide constant-time complexity for average-case operations like insertion, deletion, and lookup.
  • Dynamic Size: The size of a hash table can be increased or decreased dynamically to accommodate the number of elements.
  • Efficient Memory Usage: Hash tables are memory-efficient as they store only the necessary information.

How Hash Tables Work

Hash tables work by using a hash function to map keys to indices in an array. The hash function takes a key as input and returns an index. The key is then used to access the corresponding value in the array.

Steps in Hash Table Operations

  1. Hash Function: Compute the hash value of the key.
  2. Index Calculation: Use the hash value to calculate the index in the array.
  3. Value Storage: Store the value at the calculated index.
  4. Value Retrieval: Use the key to compute the index and retrieve the value.

Types of Hash Functions

There are several types of hash functions, including:

  • Direct Addressing: This method uses the key directly as the index.
  • Divide and Conquer: This method divides the key into parts and uses the sum or concatenation of these parts as the index.
  • Multiplication Method: This method multiplies the key with a constant and uses the fractional part as the index.

Common Operations

Here are some common operations performed on hash tables:

  • Insertion: Add a new key-value pair to the hash table.
  • Deletion: Remove a key-value pair from the hash table.
  • Lookup: Retrieve the value associated with a given key.

Example Usage

Hash tables are widely used in various applications, such as:

  • Caching: Storing frequently accessed data for faster retrieval.
  • Database Indexing: Indexing data for efficient querying.
  • Distributed Systems: Distributing data across multiple nodes.

Hash Table Example

For more information on hash tables and related data structures, check out our Data Structures Tutorial.