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Linked lists are a fundamental data structure in computer science, which store and organize data elements in a linear fashion. Each element, referred to as a node, contains a reference to the next node in the sequence. This complete guide will walk you through the concepts of linked lists, their types, and their advantages and disadvantages. We will also dive into practical examples and implementation in Python, providing a comprehensive understanding for beginners and seasoned programmers alike.

Linked lists are a dynamic data structure, which means they can grow or shrink in size during the execution of a program. Unlike arrays, they don't require a contiguous block of memory, as each element in the list is stored separately and connected through pointers or references.

### Elements of a Linked List

A linked list is made up of nodes, each containing two parts:

1. Data: The actual information or value stored in the node.
2. Next: A reference or pointer to the next node in the list.

The first node in the list is called the head and the last node is called the tail. The tail node's `next` reference points to `None`, indicating the end of the list.

There are two primary types of linked lists:

1. Singly Linked List: Each node in the list has a reference to the next node. This is the simplest form of a linked list.
2. Doubly Linked List: Each node in the list has references to both the previous node and the next node, allowing for traversal in both directions.

In this guide, we will focus on singly linked lists.

Now that we have a basic understanding of linked lists, let's see how we can implement a singly linked list in Python.

### Defining a Node

First, we need to define a `Node` class that represents an element in the list.

``````class Node:
def __init__(self, data):
self.data = data
self.next = None``````

The `Node` class has an initializer method (`__init__`) that takes a single parameter, `data`, which is the value to be stored in the node. The `next` attribute is initialized to `None`.

To create a linked list, we need a separate class that will manage the list and its operations. Let's create a `LinkedList` class with the following methods:

1. `__init__`: Initializes an empty linked list with a `head` set to `None`.
2. `is_empty`: Checks if the list is empty.
3. `length`: Returns the length of the list.
4. `append`: Adds a new node to the end of the list.
5. `insert`: Inserts a new node at a specified position.
6. `delete`: Removes a node with the given data from the list.
7. `search`: Searches for a node with the given data in the list and returns its position.
8. `display`: Prints the contents of the list.
``````class LinkedList:
def __init__(self):

def is_empty(self):

def length(self):
count = 0
while current:
count += 1
current = current.next
return count

def append(self, data):
new_node = Node(data)
if self.is_empty():
else:
while current.next:
current = current.next
current.next = new_node

def insert(self, position, data):
if position < 0 orposition > self.length():
raise IndexError("Invalid position")

new_node = Node(data)
if position == 0:
else:
for _ in range(position - 1):
current = current.next
new_node.next = current.next
current.next = new_node

def delete(self, data):
if self.is_empty():
raise ValueError("List is empty")

else:
while current.next and current.next.data != data:
current = current.next

if current.next is None:
current.next = current.next.next

def search(self, data):
position = 0
while current:
if current.data == data:
return position
position += 1
current = current.next

def display(self):
while current:
print(current.data, end=" -> ")
current = current.next
print("None")``````

With this implementation, we can create and manipulate singly linked lists. Here's an example of how to use the `LinkedList` class:

``````my_list = LinkedList()
my_list.append(1)
my_list.append(2)
my_list.append(3)
my_list.insert(1, 5)
my_list.display()  # Output: 1 -> 5 -> 2 -> 3 -> None
print(my_list.search(5))  # Output: 1
my_list.delete(5)
my_list.display()  # Output: 1 -> 2 -> 3 -> None``````

## FAQ

### 1. What is the difference between linked lists and arrays?

Arrays are a contiguous block of memory, while linked lists store elements separately and connect them through pointers. Arrays have constant-time access to elements, while linked lists require traversing the list to access elements, taking linear time. Linked lists can grow or shrink dynamically without the need for resizing, whereas arrays need resizing when they exceed their allocated capacity.

Linked lists are a better choice when you need to frequently insert or delete elements at the beginning or middle of the list, as they can do this in constant time. If you need constant-time access to elements or a fixed-size data structure, arrays might be more suitable.

### 3. How can I reverse a linked list?

To reverse a linked list, you can use an iterative or recursive approach. The iterative approach involves updating the `next` pointers of each node to point to the previous node. The recursive approach involves reversing the remaining list and updating the `next` pointer of the current node to point to the previous node.

### 4. What is the time complexity of various operations on linked lists?

Here are the time complexities of some common operations on linked lists:

• Access: O(n)
• Search: O(n)
• Insertion: O(1) at the beginning or end, O(n) at a specific position
• Deletion: O(1) at the beginning, O(n) at a specific position or the end

### 5. Can linked lists be used to implement other data structures?

Yes, linked lists can serve as a foundation for other data structures, such as stacks, queues, and symbol tables.

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