Introduction to Doubly LL

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Editorial

Introduction to Doubly Linked Lists

A doubly linked list is an extension of a singly linked list. To fully grasp doubly linked lists, it is essential to understand the concepts of singly linked lists. Let's briefly recap the basics of singly linked lists.

Singly Linked Lists

In a singly linked list, each node contains some data and a pointer to the next node in the sequence. The last node points to null, indicating the end of the list. This structure is linear and unidirectional; you can only traverse the list in one direction, from the first node to the last.

Here is a basic representation of a singly linked list: [Data] -> [Data] -> [Data] -> null

Each node stores:

Data: The value of the node.
Next Pointer: The address of the next node in the sequence.

Doubly Linked Lists

A doubly linked list improves upon the singly linked list by allowing traversal in both directions. Each node contains two pointers: one to the next node and one to the previous node. This bidirectional nature of the list offers greater flexibility in navigating and modifying the list.

Here is a basic representation of a doubly linked list: null <- [Data] <-> [Data] <-> [Data] -> null

Each node in a doubly linked list stores:

Data: The value of the node.
Next Pointer: The address of the next node.
Back Pointer: The address of the previous node.

Advantages of Doubly Linked Lists:

Bidirectional Traversal: You can traverse the list in both forward and backward directions, which can be helpful for certain operations.
More Efficient Deletion: Deleting a node is more efficient because you have direct access to the previous node, eliminating the need for traversal from the head to find the predecessor.
Insertion Operations: Inserting a node before or after a given node is simpler because you have access to both neighboring nodes.

Disadvantages:

Increased Memory Usage: Each node requires extra memory for the backward pointer, which can be a drawback for memory-constrained environments.
Complexity: The implementation is more complex compared to singly linked lists due to the additional pointer and the need to maintain pointers in both directions.

Representation in C++ and Java

In a doubly linked list, the node structure is extended to include a pointer to the previous node. Here’s how you might define it in C++:

struct Node {
    // Value of the node
    int data;        
    // Pointer to the next node
    Node* next;      
    // Pointer to the previous node
    Node* back;      

    // Constructor to initialize a node with data
    Node(int data) : data(data), next(nullptr), back(nullptr) {}
};
class Node {
    // Value of the node
    int data;        
    // Pointer to the next node
    Node next;      
    // Pointer to the previous node
    Node back;      

    // Constructor to initialize a node with data
    Node(int data) {
        this.data = data;
        this.next = null;
        this.back = null;
    }
}
class Node:
    """ Constructor to initialize a node with data """
    def __init__(self, data):
        # Value of the node
        self.data = data        
        # Pointer to the next node
        self.next = None      
        # Pointer to the previous node
        self.back = None      

    
class Node {
    // Constructor to initialize a node with data
    constructor(data) {
        // Value of the node
        this.data = data;        
        // Pointer to the next node
        this.next = null;      
        // Pointer to the previous node
        this.back = null;      
    }
}

Conclusion:

In summary, a doubly linked list is a versatile data structure that allows for bidirectional traversal by adding a backward pointer to each node. This simple modification significantly enhances the flexibility of linked lists, making it easier to navigate in both directions.

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