What Is Hashing Data Structure?


Larry Thompson

Hashing is a fundamental concept in computer science and is widely used in various applications. It is a data structure that allows efficient retrieval of data based on a key.

Hashing involves mapping the input key to an index or address in a data structure called a hash table. In this article, we will explore what hashing is, how it works, and its applications.

What is Hashing?

A hash function is at the core of hashing. It takes an input, typically a key, and returns a unique value called the hash code.

This hash code is then used as an index to store or retrieve data in the hash table. The goal of hashing is to minimize collisions, where two different keys produce the same hash code.

How does Hashing Work?

To understand how hashing works, let’s take a look at a simplified example:

  • Step 1: You have a set of keys (e.g., names of people) that need to be stored.
  • Step 2: A hash function (e., mapping each character in the name to its ASCII value and summing them up) converts each key into a unique hash code.
  • Step 3: The hash code is used as an index to store the key-value pair in the hash table.

This process allows for efficient retrieval of data since accessing an element in an array-like structure (hash table) has constant time complexity O(1).

Collision Resolution

In practice, collisions can occur when two different keys produce the same hash code. There are various techniques for handling collisions:

  • Separate Chaining: Each hash table index contains a linked list of key-value pairs with the same hash code. When a collision occurs, the new key-value pair is appended to the existing list.
  • Open Addressing: When a collision occurs, the hash table is probed sequentially until an empty slot is found.
  • Robin Hood Hashing: In this technique, keys are rearranged based on the difference between their ideal and current positions, minimizing search time.

Applications of Hashing

Hashing is used in various applications due to its efficiency and ability to quickly retrieve data. Some common applications include:

  • Data retrieval in databases
  • Password storage (hashing passwords for security)
  • Caching mechanisms (e., browser caching)
  • Spell-checking algorithms

In conclusion, hashing is a powerful data structure that allows for efficient retrieval of data based on a key. It uses a hash function to map keys to unique hash codes, which are used as indices in a hash table.

Collisions can occur but can be resolved using techniques like separate chaining or open addressing. With its wide range of applications, understanding hashing is essential for any programmer or computer science enthusiast.

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