What Is Hash Tables in Data Structure?


Angela Bailey

What Is Hash Tables in Data Structure?

Hash tables are a fundamental data structure in computer science that allow for efficient storage and retrieval of data. They are often referred to as hash maps or dictionaries in various programming languages.

Hash tables consist of an array, where each element in the array is called a bucket. Each bucket can store one or more key-value pairs.

How do hash tables work?

Hash tables use a technique called hashing to determine the index of a specific key-value pair within the array. The hashing process involves applying a hash function to the key, which converts it into an integer value.

This integer value is then used as an index to store the corresponding value within the array.

The goal of a good hash function is to distribute the keys evenly across the available buckets, minimizing collisions. Collisions occur when two different keys produce the same index value.

To handle collisions, most hash table implementations use a technique called chaining or open addressing.


Chaining involves storing multiple key-value pairs that collide into the same bucket as a linked list. When searching for a specific key, the hash table uses the hash function to determine which bucket should contain that key.

It then traverses the linked list within that bucket until it finds the desired key-value pair.

Open Addressing:

Open addressing, on the other hand, attempts to find an alternative location within the array when a collision occurs. It does this by probing or searching for an empty bucket nearby using various techniques like linear probing, quadratic probing, or double hashing.

The benefits of using hash tables:

  • Fast access: Hash tables provide fast access to elements by allowing constant time complexity for both insertion and retrieval operations on average.
  • Flexible key-value pairs: Hash tables allow any type of object to be used as a key and associate it with any other type of object as the value.
  • Efficient memory usage: Hash tables dynamically resize themselves to accommodate more elements, allowing efficient memory usage even if the number of elements changes over time.

Common use cases for hash tables:

Hash tables are widely used in various applications and programming languages due to their efficiency and versatility. Some common use cases include:

  • Caching: Hash tables are often used in caching systems to store frequently accessed data, reducing the need for expensive computations or database queries.
  • Symbol tables: Compilers and interpreters use hash tables to implement symbol tables, which store information about variables, functions, and other program identifiers.
  • Associative arrays: Hash tables serve as an excellent data structure for implementing associative arrays, where keys are associated with corresponding values.
  • Password storage: Hash functions play a crucial role in securely storing passwords. Passwords are hashed and stored in a hash table, making it difficult for attackers to retrieve the original password.

In conclusion, hash tables are a powerful data structure that allows efficient storage and retrieval of data through the use of hashing. By distributing values across an array using a hash function, hash tables provide fast access to elements while maintaining flexibility and efficient memory usage.

Their versatility makes them invaluable in numerous applications across different fields of computer science.

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