What Is Hash Function Data Structure?


Larry Thompson

A hash function is a fundamental concept in computer science and data structures. It plays a crucial role in efficiently storing and retrieving data. In this article, we will explore what a hash function is and how it works.

What Is a Hash Function?
A hash function is a mathematical function that takes an input (or “key”) and produces a fixed-size string of characters, known as the hash value or hash code. The key can be of any length or type, such as a string, number, or even an entire file.

How Does a Hash Function Work?
The main purpose of a hash function is to quickly map data to a fixed-size array or table called a hash table. It achieves this by converting the input key into an index within the range of the array’s size. This index determines where the data will be stored in the hash table.

Hashing Process:

  • The input key is passed through the hash function.
  • The hash function computes the corresponding index based on the key’s value.
  • The data associated with the key is then stored at that index in the hash table.

Collision Resolution
Collisions occur when two different keys produce the same index value within the hash table. Handling collisions is an important aspect of implementing a reliable hashing algorithm.

Common Collision Resolution Techniques:

  • Separate Chaining: In this technique, each element in the hash table corresponds to a linked list. When collisions occur, new elements are appended to these lists at their respective indices.
  • Open Addressing: Here, when there is a collision, additional probing methods such as linear probing (checking next available slot) or quadratic probing (checking slots based on a quadratic function) are used to find the next available slot in the hash table.

Applications of Hash Functions
Hash functions are widely used in various applications, including:

Data Retrieval: Hash tables provide fast data retrieval by mapping keys to their corresponding values in constant time. This is especially useful when dealing with large datasets.

Password Storage: Hash functions play a critical role in securely storing passwords. Instead of storing actual passwords, systems store their hash values. During authentication, the password entered by the user is hashed and compared against the stored hash value.

Data Integrity: Hash functions are commonly used to verify the integrity of data. By calculating the hash value of a file or message, you can compare it to a known hash value to ensure that the data has not been tampered with.


Hash functions are an essential concept in computer science and data structures. They provide efficient ways to store and retrieve data by mapping keys to their corresponding indices within a hash table. Understanding how hash functions work and how collisions are resolved is crucial for designing efficient algorithms and systems that rely on hashing.

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