by Jasleen Chhabra | Updated on 24 August 2024

Linked lists are one of the most fundamental and flexible data structures in computer science. Unlike arrays, linked lists do not store elements in contiguous memory locations, which allows for more efficient memory usage and dynamic resizing. Understanding linked lists is essential for tackling various complex problems in data structure and algorithm design.

What is a Linked List?

A linked list is a linear data structure where each element is a separate object called a node. Each node contains two parts: the data and a reference (or link) to the next node in the sequence. The primary benefit of a linked list over a conventional array is its dynamic size and ease of insertion/deletion.

Types of Linked Lists

1. Singly Linked List: Each node points to the next node in the sequence, and the last node points to null, indicating the end of the list.
2. Doubly Linked List: Each node has two links, one pointing to the next node and one pointing to the previous node. This allows traversal in both directions.
3. Circular Linked List: The last node points back to the first node, forming a circle. This can be either singly or doubly linked.

Key Features of Linked Lists

• Dynamic Size: Unlike arrays, linked lists do not have a fixed size. They grow and shrink as needed.
• Ease of Insertion/Deletion: Nodes can be easily inserted or removed without reorganizing the entire structure, unlike arrays where elements might need to be shifted.

Basic Operations on Linked Lists

1. Insertion: Adding a new node to the linked list.
2. Deletion: Removing an existing node from the linked list.
3. Traversal: Accessing each node in the linked list in a sequential manner.
4. Searching: Finding a node with a specific value.

Advantages of Linked Lists

• Dynamic Size: Can grow or shrink in size efficiently.
• Efficient Insertions/Deletions: Easier to insert and delete elements compared to arrays, especially for large datasets.

Disadvantages of Linked Lists

• Memory Usage: Requires extra memory for storing pointers.
• Sequential Access: Slower access time compared to arrays, as elements can only be accessed sequentially from the start.

Implementation of a Singly Linked List in C++

Here's a basic implementation of a singly linked list in C++:

#include <iostream>

class Node {
public:
    int data;
    Node* next;

    Node(int data) {
        this->data = data;
        this->next = nullptr;
    }
};

class LinkedList {
private:
    Node* head;

public:
    LinkedList() {
        head = nullptr;
    }

    void insert(int data) {
        Node* newNode = new Node(data);
        if (head == nullptr) {
            head = newNode;
        } else {
            Node* temp = head;
            while (temp->next != nullptr) {
                temp = temp->next;
            }
            temp->next = newNode;
        }
    }

    void deleteNode(int key) {
        Node* temp = head;
        Node* prev = nullptr;

        if (temp != nullptr && temp->data == key) {
            head = temp->next;
            delete temp;
            return;
        }

        while (temp != nullptr && temp->data != key) {
            prev = temp;
            temp = temp->next;
        }

        if (temp == nullptr) return;

        prev->next = temp->next;
        delete temp;
    }

    void display() {
        Node* temp = head;
        while (temp != nullptr) {
            std::cout << temp->data << " -> ";
            temp = temp->next;
        }
        std::cout << "null" << std::endl;
    }
};

int main() {
    LinkedList list;
    list.insert(10);
    list.insert(20);
    list.insert(30);
    list.display();

    list.deleteNode(20);
    list.display();

    return 0;
}
 

Practical Applications of Linked Lists

1. Dynamic Memory Allocation: Linked lists are used in dynamic memory allocation schemes.
2. Implementation of Data Structures: Other data structures like stacks, queues, and graphs are often implemented using linked lists.
3. Efficient Insertions/Deletions: Useful in applications where frequent insertions and deletions are required, such as in-memory databases and transactional systems.
4. Real-Time Systems: Used in real-time computing systems for task scheduling.

Conclusion

Linked lists are a powerful and flexible data structure that provides dynamic memory management capabilities. They are essential for implementing other complex data structures and solving problems that require efficient insertions and deletions. Understanding the basics and various types of linked lists, along with their advantages and disadvantages, is crucial for any programmer or computer scientist.

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