# Linked list in data structure

## Introduction

Data structures are fundamental concepts in computer science and programming. They provide a way to organize and store data efficiently, allowing for faster and more effective operations. One such popular data structure is the linked list. If you’re a beginner in programming or computer science, you might have come across the term “linked list” and wondered, “What is a linked list?” In this comprehensive guide, we’ll delve into the world of linked lists and explore their types, advantages, disadvantages, and more.

## What is a Linked List?

At its core, a linked list is a linear data structure that stores a collection of elements, called nodes, in a sequential manner. Unlike arrays, which store elements in contiguous memory locations, linked lists use pointers or references to connect the nodes, creating a chain-like structure. Each node in a linked list contains data and a pointer/reference to the next node in the sequence, forming a link between them. This is where the name “linked list” comes from.

Linked lists come in various types, each with its own characteristics and use cases. Let’s take a closer look at some of the common types of linked list in data structure :

In a singly linked list, each node has a data field and a pointer/reference to the next node in the sequence. It only allows traversal in one direction, usually from the head (the first node) to the tail (the last node). The tail node has a null pointer/reference, indicating the end of the list.

In a doubly linked list, each node has a data field and two pointers/references – one to the next node and one to the previous node in the sequence. This allows for traversal in both directions, making it more versatile than a singly linked list. However, it requires extra memory to store the additional pointer/reference.

A circular linked list is similar to a singly linked list, except that the tail node’s pointer/reference points back to the head node, forming a loop. This creates a circular structure, and traversal can start from any node and continue indefinitely.

A circular doubly linked list combines the features of both circular and doubly linked lists. Each node has a data field, a pointer/reference to the next node, and a pointer/reference to the previous node. The tail node’s pointer/reference points back to the head node, forming a circular structure that allows for traversal in both directions.

## How Does a Linked List Work?

Linked lists operate based on the concept of nodes and pointers/references. The nodes store the actual data, and the pointers/references connect the nodes, forming a chain-like structure. Let’s take a closer look at how a linked list works:

To create a linked list, you start with an empty list and add nodes to it. Each node contains data and a pointer/reference to the next node in the sequence. The first node that you add becomes the head of the list, and the last node becomes the tail. The tail node’s pointer/reference points to null, indicating the end of the list.

Traversal refers to the process of accessing each node in a linked list sequentially. In a singly linked list, you start from the head and follow the pointers/references to the next node until you reach the tail, which has a null pointer/reference. In a doubly linked list, you can traverse in both directions, starting from either the head or the tail, by following the pointers/references to the next and previous nodes.

### Inserting into a Linked List:

Insertion is a common operation in linked lists, and it can be performed at various positions, such as the beginning, middle, or end of the list. To insert a new node, you first create a new node with the data you want to insert and update the pointers/references of the surrounding nodes to connect them to the new node appropriately. For example, to insert a node at the beginning of a singly linked list, you update the pointer/reference of the new node to point to the current head, and then update the head to point to the new node.

### Deleting from a Linked List:

Deletion is another common operation in linked lists, and it involves removing a node from the list. To delete a node, you update the pointers/references of the surrounding nodes to bypass the node you want to delete. For example, to delete a node from a singly linked list, you update the pointer/reference of the previous node to point to the next node, bypassing the node you want to delete.

### Searching in a Linked List:

Searching for a specific node or data in a linked list requires traversing the list and comparing the data in each node with the target data. If a match is found, you can perform the desired operation on that node. However, searching in a linked list can be less efficient than in other data structures like arrays, as it requires linear traversal from the head to the tail, which can have a time complexity of O(n) for a list of n nodes.

Linked lists offer several advantages in certain scenarios, making them a popular choice in certain applications. Some of the advantages of linked lists include:

1. Dynamic Size:
Unlike arrays, which have a fixed size, linked lists can grow or shrink dynamically as new nodes are added or deleted. This makes linked lists more flexible and efficient in managing varying amounts of data.
2. Efficient Insertion/Deletion:
Insertion and deletion operations can be performed more efficiently in linked lists compared to arrays, as they only require updating the pointers/references of adjacent nodes, rather than shifting elements like in arrays.
3. No Wasted Memory:
Linked lists do not require a contiguous block of memory like arrays, which can result in wasted memory due to fragmentation. Linked lists utilize memory more efficiently by using pointers/references to connect nodes wherever they are in the memory.
4. Versatility:
Linked lists come in various types, such as singly linked lists, doubly linked lists, circular linked lists, etc., offering versatility in choosing the right type for a specific application. For example, doubly linked lists allow for traversal in both directions, making them suitable for certain operations like reverse traversal.

While linked lists offer several advantages, they also have some limitations that need to be considered in certain scenarios. Some of the disadvantages of linked lists include:

### Lack of Random Access:

Unlike arrays, which allow for direct access to any element using an index, linked lists require sequential traversal from the head to the desired node, which can result in slower access times. This makes linked lists less suitable for applications that require frequent random access to elements.

It requires additional memory for storing the pointers/references that connect the nodes, which can result in increased memory overhead compared to arrays. This can be a concern in applications with limited memory resources.

### Difficulty in Reverse Traversal:

While doubly linked lists allow for efficient reverse traversal, singly linked lists require additional effort to traverse in reverse order. This can be a limitation in certain scenarios where reverse traversal is a common operation.

### Extra Complexity:

Linked lists introduce the concept of pointers/references, which can add complexity to the implementation and maintenance of the data structure. This can be challenging for developers who are not familiar with pointer-based operations.

### Lack of Cache Friendliness:

It does not have good cache performance compared to arrays, as the elements in a linked list may not be stored in contiguous memory locations. This can result in more cache misses, leading to slower access times in certain scenarios.

## Conclusion

In conclusion, a linked list is a dynamic data structure that consists of a collection of nodes where each node contains a data element and a pointer to the next node in the list. It is used in various applications such as stacks, queues, dynamic memory allocation, and graph/tree representations. They have advantages in terms of dynamic resizing, efficient insertion/deletion at the beginning or end of the list, and flexibility. However, they also have limitations in terms of linear traversal/searching time complexity and lack of constant-time access based on an index.