What are linked lists and how do you implement them in C++?

Definition

A linked list is a linear data structure where elements, called nodes, are stored in separate memory locations and connected using pointers. Each node contains two parts:

• Data: The value stored in the node.
• Pointer: A reference to the next node in the sequence.

Unlike arrays, linked lists allow efficient insertion and deletion of elements without shifting other elements.

Implementation in C++

A simple singly linked list in C++ uses a struct to define a node and pointers to connect nodes.

Step-by-Step Example

Goal: Create a linked list with three nodes containing the values 10, 20, and 30.

1. Define the Node Structure:

``cpp
struct Node {
int data;
Node next;
};
`

2. Create Nodes and Link Them:

`cpp
Node head = new Node();
Node second = new Node();
Node third = new Node();

head->data = 10;
head->next = second;

second->data = 20;
second->next = third;

third->data = 30;
third->next = nullptr;
`

3. Traverse and Print the List:

`cpp
Node* current = head;
while (current != nullptr) {
std::cout data next;
}
// Output: 10 20 30
``

Diagram

Suppose the list is:

$$ \text{head} \longrightarrow [10|\cdot] \longrightarrow [20|\cdot] \longrightarrow [30|\text{nullptr}] $$

Takeaways

• A linked list stores elements in nodes connected by pointers, allowing dynamic memory allocation.
• In C++, linked lists are implemented using structs/classes and pointers.
• Linked lists enable efficient insertion and deletion but require extra memory for pointers.