Why a HashMap is faster than an Array?

Why a HashMap is faster than Array?

In computer science, storing and retrieving objects or elements from a group of things is very important. The way you store data and how easily (or better to say, how quickly) you can access the data from a group of lots of different data sets is a crucial process. Data structures like Arrays and HashMaps are different ways you can store data. But to understand why a HashMap is faster than Array, we need to understand the anatomy of each data structure.

In this article, we will explore the inner workings of HashMap and delve into the reasons why it is considered faster compared to other data structures. So, if you are interested in understanding the speed and efficiency of HashMap, keep reading to uncover the secrets behind its superior performance.

What is an Array?

An Array is one of the fundamental data structures in Computer science that stores a collection of elements of the same type in contiguous memory locations.

key characteristics of Array

Homogeneous Nature

An array data structure is homogenous, which means it can only store elements of the same data type, such as integers, characters, or objects.

Index-Based Access

Each element in an array is accessed using an index. The index represents the element’s position within the array, typically starting from 0 in many programming languages.

Fixed Size

In most programming languages, arrays have a fixed size, meaning the number of elements they can store is determined when the array is created. Some languages provide dynamic arrays (like JS and Python) or resizable arrays to work around this limitation.

Contiguous Memory Allocation

The elements of an array are stored in contiguous memory locations, which allows for efficient memory access and iteration.

Common Operations

Arrays support common operations such as adding or removing elements, accessing elements by index, and iterating through the elements.


Arrays are widely used for various applications, including storing lists of items, implementing vectors and matrices, and representing data structures such as stacks and queues.

Array Data structure

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What is a HashMap?

HashMap is a widely used data structure in computer programming that allows for efficient search, insertion, and deletion of key-value pairs. But have you ever wondered why HashMap is considered faster than other data structures? The answer lies in its underlying implementation and the technique it uses, called hashing.

key characteristics of HashMap

Key-Value Storage

A hashmap stores data in the form of key-value pairs. Each key is unique within the hashmap, and the associated value can be accessed or modified using the key.


Hashmaps use a hashing function to map keys to specific positions in an underlying array. The hashing function takes a key as input and produces a hash code, which is used to determine the index where the key-value pair will be stored.

Fast Lookup

One of the main advantages of hashmaps is their ability to provide fast lookup operations. Given a key, the hashing function allows for quick determination of the associated value’s storage location, leading to efficient retrieval.

Dynamic Sizing

Many hashmap implementations support dynamic resizing, allowing the capacity of the underlying array to grow or shrink as the number of key-value pairs changes. This helps maintain efficient performance as the size of the data set changes.


In the average and worst cases, the time complexity of insertion, deletion, and lookup operations in a hashmap is O(1), making it a highly efficient data structure for many use cases.

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What is Hashing and what is its role in HashMap?

Hashing is converting input data (such as a key in a hashmap) into a fixed-size value, typically a hash code or hash value, using a hash function. In layman’s terms, when the user inputs the key in Hashmap, with the help of the Hash function, it generates a unique fixed-size value. The idea is to map the inputted key to a specific location in a data structure, such as an array in the case of hashmaps.

The hash value produced by the hash function is used to determine where the key-value pair will be stored. By using hashing to map keys to specific locations, hashmaps can provide efficient lookup operations.

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Why a HashMap is faster than an Array?

The time complexity of the lookup operation in an array and a hashmap varies depending on the resources and type of implementation. Here’s a comparison of the time complexity for the lookup operation in both data structures:


In Array’s case, if you already know the value of the index where your elements are present then the time complexity of the Hashmap is O(1), which is the best-case time complexity.

But if you don’t know the index then the time complexity of retrieving an element from an array can be O(n), which is the worst time complexity.


Note:- Since HashMap utilizes an array as its underlying structure, its performance cannot surpass that of a correctly utilized array.

On average, the time taken to retrieve a value from a hashmap is constant O(1), irrespective of the number of entries in the hashmap. This is based on the assumption of a good hash function and uniform distribution of keys.

In the worst-case scenario, due to hash collisions or poor hash function performance, the time complexity for lookup can degrade to linear time O(n).

It’s important to note that the time complexities mentioned above are based on ideal scenarios and can vary based on factors such as hash function performance, hash collisions, load factor, and specific implementations of hashmap data structures.

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Final Words

In conclusion, HashMap is faster than other data structures for several reasons. Its constant time complexity for basic operations such as retrieving and inserting elements makes it highly efficient. Additionally, HashMap’s ability to handle collisions and dynamically resize itself ensures optimal performance even with many elements. By sharing and commenting on this topic, we can further explore the advantages and potential applications of HashMap in professional settings.

In summary, HashMap is faster than other data structures due to its efficient key-value pair storage and retrieval implementation. Its ability to quickly calculate hash codes and handle collisions makes it a preferred choice in many programming scenarios. However, it is important to note that the performance of HashMap can vary depending on factors such as load factor and the quality of the hash function used. If you found this information helpful, please consider sharing this article and leaving a comment below to further the discussion.


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