Insert at End of Doubly Linked List in DSA Python - Build from Scratch

Insert at End of Doubly Linked List

📖 Scenario: You are managing a playlist of songs. Each song is linked to the previous and next song, allowing easy navigation back and forth. You want to add a new song to the end of the playlist.

🎯 Goal: Build a doubly linked list and write code to insert a new node at the end. Finally, print the playlist from start to end.

📋 What You'll Learn

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

Create a doubly linked list with three nodes containing data 10, 20, and 30

Create a variable new_data with value 40

Write a function insert_at_end(head, data) that inserts a new node with data at the end of the list

Print the list from head to end showing node data separated by -> and ending with null

💡 Why This Matters

🌍 Real World

Doubly linked lists are used in music players, web browsers, and undo-redo features where you need to move forward and backward easily.

💼 Career

Understanding linked lists is fundamental for software developers, especially for roles involving data structure optimization and system design.

1

Create the initial doubly linked list

Create a Node class with data, prev, and next attributes. Then create three nodes with data 10, 20, and 30 linked as a doubly linked list. Assign the first node to a variable called head.

DSA Python

# Your code here

Hint

Define the Node class first. Then create three nodes and link them using next and prev pointers.

2

Create the new data to insert

Create a variable called new_data and set it to 40.

DSA Python

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

node1 = Node(10)
node2 = Node(20)
node3 = Node(30)

node1.next = node2
node2.prev = node1
node2.next = node3
node3.prev = node2

head = node1

# Your code here

Hint

Just create a variable new_data and assign it the value 40.

3

Write the function to insert at the end

Write a function called insert_at_end(head, data) that creates a new node with data and inserts it at the end of the doubly linked list starting at head. Return the head of the updated list.

DSA Python

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

node1 = Node(10)
node2 = Node(20)
node3 = Node(30)

node1.next = node2
node2.prev = node1
node2.next = node3
node3.prev = node2

head = node1

new_data = 40

def insert_at_end(head, data):
    # Your code here

Hint

Start from head and move to the last node. Then link the new node after it.

4

Print the updated doubly linked list

Call insert_at_end(head, new_data) and assign the result back to head. Then print the list from head to end. Print each node's data followed by -> , ending with null.

DSA Python

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

node1 = Node(10)
node2 = Node(20)
node3 = Node(30)

node1.next = node2
node2.prev = node1
node2.next = node3
node3.prev = node2

head = node1

new_data = 40

def insert_at_end(head, data):
    new_node = Node(data)
    if head is None:
        return new_node
    current = head
    while current.next is not None:
        current = current.next
    current.next = new_node
    new_node.prev = current
    return head

head = insert_at_end(head, new_data)

# Your code here

Hint

Traverse from head to the end, printing each node's data followed by -> . End with null.