What Is Hashing in Data Structure W3schools?


Heather Bennett

Hashing is an important concept in data structures that plays a crucial role in organizing and retrieving data efficiently. In this tutorial, we will explore what hashing is and how it works in the context of W3schools.

What is Hashing?

Hashing is a technique used to map data to a fixed-size array, usually called a hash table or hash map. The process involves applying a hash function to the data, which generates a unique hash code or hash value. This hash value is then used as an index to store the data in the hash table.

Hash Functions

A hash function takes an input (data) and returns a fixed-size string of characters, which represents the unique identifier for that input. The key properties of a good hash function are:

  • Uniformity: A good hash function should evenly distribute the keys across the available slots in the hash table.
  • Deterministic: Given the same input, it should always produce the same output.
  • Efficiency: It should be computationally efficient to calculate.

The Hash Table

The hash table is an array of fixed size that stores key-value pairs. Each element in the array is called a bucket or slot. When inserting data into the hash table, the key is hashed using the chosen hashing algorithm and then stored at the corresponding slot indicated by its computed index.

Collision Resolution

Collisions occur when two different keys generate the same hash value and try to occupy the same slot in the hash table. There are several methods for resolving collisions:

1. Chaining

Chaining involves maintaining linked lists at each slot of the hash table. If two keys produce the same index, they are appended to the linked list at that index. This way, multiple values can be stored at the same slot without overwriting each other.

2. Open Addressing

Open addressing is an alternative collision resolution method where, upon a collision, the algorithm looks for the next available slot in the hash table to store the data. Various open addressing techniques include linear probing, quadratic probing, and double hashing.

Advantages of Hashing

  • Fast Data Retrieval: Hashing allows for constant-time retrieval of data since accessing an element in an array has a time complexity of O(1) on average.
  • Efficient Memory Usage: Hash tables can be more memory-efficient compared to other data structures like arrays or linked lists.
  • Data Integrity: Hash functions help ensure data integrity by generating unique identifiers for each input.


Hashing is a powerful technique used in data structures to efficiently store and retrieve data. It provides fast retrieval times, efficient memory usage, and helps maintain data integrity. Understanding hashing is essential for building efficient algorithms and working with large datasets.

Now that you have a good understanding of what hashing is and how it works in W3schools, you can start implementing it in your own projects. Happy coding!

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