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

Delete from End of Doubly Linked List

📖 Scenario: You are managing a playlist of songs using a doubly linked list. Each song is a node with a title. You want to remove the last song from the playlist.

🎯 Goal: Build a doubly linked list with 3 songs, then delete the last song from the list, and finally print the updated playlist from start to end.

📋 What You'll Learn

Create a doubly linked list with exactly 3 nodes containing song titles: 'Song1', 'Song2', 'Song3'

Create a variable called head that points to the first node

Create a function called delete_from_end that deletes the last node from the doubly linked list

Print the playlist from start to end after deletion in the format: Song1 -> Song2 -> null

💡 Why This Matters

🌍 Real World

Doubly linked lists are used in music players, browsers, and other apps to move forward and backward through items efficiently.

💼 Career

Understanding linked lists and how to modify them is a key skill for software developers working with data structures and memory management.

1

Create the doubly linked list with 3 songs

Define a class called Node with attributes data, prev, and next. Then create 3 nodes with data 'Song1', 'Song2', and 'Song3'. Link them to form a doubly linked list. Finally, create a variable called head that points to the first node.

DSA Python

# Define Node class and create 3 linked nodes
# Your code here

Hint

Remember to link each node's next and prev pointers correctly to form the doubly linked list.

2

Create a helper variable to track the current node

Create a variable called current and set it equal to head. This will help us traverse the list.

DSA Python

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

node1 = Node('Song1')
node2 = Node('Song2')
node3 = Node('Song3')

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

head = node1

# Create a variable current and set it to head
# Your code here

Hint

This variable will help us move through the list to find the last node.

3

Write the function to delete the last node

Define a function called delete_from_end that takes head as input. Inside, use a variable current to traverse to the last node. Then update the second last node's next to None to remove the last node. Return the updated head.

DSA Python

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

node1 = Node('Song1')
node2 = Node('Song2')
node3 = Node('Song3')

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

head = node1

current = head

def delete_from_end(head):
    # Your code here

Hint

Traverse to the last node, then disconnect it by setting the previous node's next to None.

4

Print the playlist after deleting the last song

Call delete_from_end(head) and update head with the returned value. Then use a while loop with a variable current starting at head to print each song's data followed by ' -> '. After the loop, print 'null'.

DSA Python

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

node1 = Node('Song1')
node2 = Node('Song2')
node3 = Node('Song3')

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

head = node1

current = head

def delete_from_end(head):
    if head is None:
        return None
    current = head
    while current.next is not None:
        current = current.next
    if current.prev is not None:
        current.prev.next = None
    else:
        head = None
    return head

# Delete last node and print playlist
# Your code here

Hint

After deleting the last node, print all remaining nodes followed by ' -> ', then print 'null'.