Difference Between Array and Linked List

Both arrays and linked lists are important and simple ways of storing and performing operations on data. A linked list is made up of a number of nodes, which are connected by links (pointers) to the next node, while an array is a contiguous piece of memory. This is a simple difference between them, which has implications for performance in memory management and also how you can use each within an application. We will discuss arrays and linked lists in this article and then compare both structures to evaluate how they differ in various factors.

Table of Contents:

• What is an Array?
• What is a Linked List?
• Difference between Array and Linked List
  • Basic Definition
  • Size
  • Storage Allocation
  • Order of the Elements
  • Accessing the Element
  • Insertion and Deletion of Elements
  • Searching
  • Memory Required
  • Memory Utilization
• When to Use an Array and a Linked List?
• Array vs Linked List: Time Complexity
• Array vs Linked List: Space Complexity
• Conclusion

What is an Array?

An array is a collection of elements that are kept in contiguous memory locations in computer memory. All elements in an array have the same data type, which is true in many computer languages, and are accessed with the same index, usually starting with 0. Arrays are static; in simple terms, you can say that when you declare an array, its size is fixed.

Example:

int arr[5] = {10, 20, 30, 40, 50};

Here, arr[0] is 10, arr[1] is 20, and so on.

What is a Linked List?

A linked list is a linear data structure in which elements, called nodes, are stored in non-contiguous memory addresses. Each node consists of two parts:

• Data: The actual value.
• Pointer (Next): The address of the next node in the list.
  

There are different types of linked lists:

• Singly Linked List: It is a type of linked list in which each node points to the next node.
• Doubly Linked List: A type of linked list in which each node points to the next node and the previous node.
• Circular Linked List: It is also a type of linked list in which the last node points back to the first node.

Difference between Array and Linked List

Below are some differences between an array and a linked list, which are briefly discussed.

1. Basic Definition

An array is a set of elements that share a memory called contiguous memory, which allows for indexing, while a linked list is a sequence of nodes, where each node contains the data and a pointer to the next node. Also, accessing data in an array is quick and easier.

2. Size

An array has a fixed size provided at the time of creation and cannot change after that, while a linked list is dynamic in size, in which the elements may be added or removed from memory whenever necessary at runtime. Using linked lists gives us the ability to dynamically use memory in the order that it fits, specifically if we are unsure of the size of the data. 

3. Storage Allocation

Arrays use static memory allocation, which means that memory is allocated in a single block when it is declared. In contrast, linked lists use dynamic memory allocation, where each node is created individually as needed. Array elements are stored in contiguous memory, while linked list nodes can be scattered throughout memory. This makes linked lists more memory-efficient than arrays in dynamic scenarios, but with additional pointer overhead.

4. Order of the Elements

An array maintains order since the elements exist next to each other in memory locations. A linked list maintains order using pointers in each node, which point to the next element. If a pointer is lost, the list becomes broken, but order is inherent to arrays due to index-based access

5. Accessing the Element

Arrays allow direct (random) access to any element using its index, making access time O(1). Linked lists require sequential traversal from the head to access a specific element, resulting in O(n) time. This makes arrays more efficient for read-heavy operations where quick access is needed. Linked lists trade off access speed for flexibility in memory and modification.

6. Insertion and Deletion of Elements

In arrays, insertion and deletion (especially in the middle or beginning) require shifting elements, making them O(n) operations. In linked lists, insertion and deletion are more efficient, O(1) if done at the head or with a known pointer, since only links need updating. Arrays are better when the structure is mostly static, while linked lists excel in dynamic data scenarios. This makes linked lists ideal for frequent add or remove operations.

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7. Searching

Arrays support both linear search (O(n)) and binary search (O(log n)) if sorted, offering faster lookup in ordered data. Linked lists only allow linear search (O(n)), as there is no direct access or index-based lookup. This makes arrays more efficient for search-heavy tasks, especially with sorted data. Linked lists are less suitable when fast searching is a priority.

8. Memory Required

Arrays need one large, contiguous block of memory, which can lead to over-allocation and wasted space. Linked lists waste a little more memory overall since you need extra memory to hold the pointers in each node. While arrays are more memory-efficient per element, linked lists provide flexibility at the cost of overhead. Ultimately, whether you select arrays or linked lists depends on how important memory minimization is and how important flexibility is.

9. Memory Utilization

Arrays can waste memory if the allocated size is too big or too small. If there are unused elements in an array, you are wasting memory, and if the array is resized, a new array must be created. Linked lists are better at using memory because they utilize memory as the elements are added. However, linked lists introduce additional memory overhead because they store a pointer in each node.

When to Use an Array and a Linked List?

Here are a few points about each array and linked list that will help you to understand which one to use when:

When to Use Arrays

1. Use arrays whenever you need to access elements by index quickly in constant time.
2. Arrays are ideal when the total number of elements is known and fixed up front.
3. They also work well if you need to read elements often.
4. When memory overhead needs to be as small as possible, arrays are typically better.
5. Use arrays whenever it is predictable and sequential to process data.
6. Sorting and searching algorithms typically perform better on arrays.

When to Use Linked Lists

1. You can use linked lists when the size of the data structure is subject to change too frequently, and there are many insert and delete operations. 
2. Use linked lists when data would require dynamic memory allocation. 
3. When you want to avoid shifting elements when inserting or deleting elements, use linked lists.
4. Use linked lists when data needs to grow or shrink during runtime. 
5. When there is no need to consider memory fragmentation, you can use linked lists.

Array vs Linked List: Time Complexity

Array vs Linked List: Space Complexity

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Conclusion

Arrays and linked lists are two important data structures. Each of these structures has its strengths and weaknesses. Arrays are favorable in situations where you need quick access to elements in the structure and low memory overhead. Linked lists are a better choice whenever you need to add or remove items. Understanding when to use an array or a linked list gives you the ability to write better programs and save both time and memory.

Difference Between Array and Linked List – FAQs