Doubly Linked List Structure and Node Design in DSA Python - Build from Scratch

Doubly Linked List Structure and Node Design

📖 Scenario: Imagine you are building a simple music playlist app. Each song in the playlist needs to be connected to the previous and next songs so users can easily move forward or backward.

🎯 Goal: You will create the basic building blocks of a doubly linked list by designing the Node class and the DoublyLinkedList class with methods to add nodes. This will help you understand how songs are linked in both directions.

📋 What You'll Learn

Create a Node class with data, prev, and next attributes

Create a DoublyLinkedList class with a head attribute initialized to None

Add a method append in DoublyLinkedList to add a new node at the end

Print the playlist forward showing each node's data connected by arrows

💡 Why This Matters

🌍 Real World

Doubly linked lists are used in music players, web browsers, and photo viewers to move back and forth between items easily.

💼 Career

Understanding doubly linked lists helps in software development roles that involve data structure design, memory management, and building efficient navigation systems.

1

Create the Node class

Create a class called Node with an __init__ method that takes a parameter data. Inside the method, set self.data = data, self.prev = None, and self.next = None.

DSA Python

# Your code here

Hint

Think of Node as a box that holds a song name and links to the previous and next songs.

2

Create the DoublyLinkedList class with head

Create a class called DoublyLinkedList with an __init__ method that sets self.head = None.

DSA Python

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

# Your code here

Hint

The DoublyLinkedList class will manage the playlist starting from the first song called head.

3

Add append method to add nodes at the end

Inside the DoublyLinkedList class, create a method called append that takes a parameter data. This method should create a new Node with data. If self.head is None, set self.head to the new node. Otherwise, traverse the list to the last node and link the new node after it by setting the last node's next to the new node and the new node's prev to the last node.

DSA Python

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

class DoublyLinkedList:
    def __init__(self):
        self.head = None

    # Your code here

Hint

Think of adding a new song at the end of the playlist. You find the last song and link the new one after it.

4

Print the playlist forward

Create a method called print_forward inside the DoublyLinkedList class. This method should start from self.head and print each node's data followed by -> until the last node, then print None. After defining the class, create a DoublyLinkedList object called playlist, append the songs 'Song1', 'Song2', and 'Song3' to it, and call playlist.print_forward() to display the playlist.

DSA Python

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

class DoublyLinkedList:
    def __init__(self):
        self.head = None

    def append(self, data):
        new_node = Node(data)
        if self.head is None:
            self.head = new_node
            return
        last = self.head
        while last.next:
            last = last.next
        last.next = new_node
        new_node.prev = last

    # Your code here

# Your code here

Hint

Print each song followed by an arrow until you reach the end, then print None to show the playlist ends.