What Is Hashtable in Data Structure?


Scott Campbell

A Hashtable is a data structure that is used to store and retrieve data in an efficient manner. It is a collection of key-value pairs, where each key is unique. In other words, it maps keys to values, allowing for quick and easy access to the data.

Why Use Hashtable?

Hashtable provides constant-time performance for basic operations such as insertion, deletion, and retrieval. This makes it an ideal choice when you need fast access to a large amount of data.

One of the main advantages of using a Hashtable is its ability to handle large amounts of data without sacrificing performance. Unlike arrays or lists, which require searching through all elements sequentially, a Hashtable uses hashing algorithms to directly access the desired value based on its key.

How Does Hashtable Work?

When you insert a key-value pair into a Hashtable, it computes the hash code of the key using a hashing algorithm. The hash code is then used as an index to store the value in an array-like structure called a bucket.

If two different keys produce the same hash code (known as a hash collision), the Hashtable uses a technique called chaining. Chaining involves storing multiple values in the same bucket using linked lists or other similar structures.

Retrieving Values from Hashtable

To retrieve a value from a Hashtable, you provide the corresponding key. The hashtable then computes the hash code of the key and uses it to locate the bucket where the value is stored. If there are multiple values in that bucket due to chaining, it traverses through them until it finds the correct value.

Hashtable vs. Other Data Structures

Hashtable offers several advantages over other data structures in certain scenarios. Here are some comparisons:

  • Arrays: Arrays have constant-time access but require sequential searching. Hashtable provides faster access with its hashing technique.
  • Lists: Lists have variable access times depending on the position of the element.

    Hashtable provides constant-time access regardless of the size of the data.

  • Binary Search Trees: Binary search trees provide efficient searching but require additional memory for storing pointers. Hashtable uses less memory by directly indexing the data.


A Hashtable is a powerful data structure that offers fast access to large amounts of data. It is ideal for scenarios where quick retrieval and insertion are crucial. By using hashing algorithms, it provides constant-time performance and ensures efficient storage and retrieval.

Remember to choose the appropriate data structure based on your specific needs. Hashtable is just one option among many, and understanding its strengths and weaknesses will help you make informed decisions when designing your applications.

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