Insert at End of Doubly Linked List in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a doubly linked list?

A doubly linked list is a chain of nodes where each node has three parts: data, a pointer to the next node, and a pointer to the previous node. This allows moving forward and backward through the list.

beginner

What steps are needed to insert a new node at the end of a doubly linked list?

1. Create a new node with the given data.<br>2. If the list is empty, make the new node the head.<br>3. Otherwise, traverse to the last node.<br>4. Set the last node's next pointer to the new node.<br>5. Set the new node's previous pointer to the last node.<br>6. Set the new node's next pointer to None.

beginner

Why do we need to update the previous pointer of the new node when inserting at the end?

Because the new node must know which node comes before it to maintain the doubly linked list structure, allowing backward traversal.

intermediate

What happens if you forget to set the new node's next pointer to None when inserting at the end?

The list may have incorrect links, possibly causing traversal errors or infinite loops because the new node might point to an unexpected node.

beginner

Show the Python code snippet to insert a node at the end of a doubly linked list.

class Node:<br>    def __init__(self, data):<br>        self.data = data<br>        self.next = None<br>        self.prev = None<br><br>class DoublyLinkedList:<br>    def __init__(self):<br>        self.head = None<br><br>    def insert_at_end(self, data):<br>        new_node = Node(data)<br>        if not self.head:<br>            self.head = new_node<br>            return<br>        last = self.head<br>        while last.next:<br>            last = last.next<br>        last.next = new_node<br>        new_node.prev = last<br>        new_node.next = None

What pointer of the new node must be set when inserting at the end of a doubly linked list?

A prev pointer to None

B next pointer to the head node

C prev pointer to the last node

D next pointer to the previous node

The new node's prev pointer must point to the last node to maintain the backward link.

If the doubly linked list is empty, what should the insert_at_end function do?

A Set the new node as the head

B Return without inserting

C Set the new node's next to head

D Set the new node's prev to head

When the list is empty, the new node becomes the head of the list.

Which traversal is needed to insert at the end of a doubly linked list?

A Traverse from tail to head

B Traverse only one node

C No traversal needed

D Traverse from head to last node

We must traverse from the head to find the last node to insert after it.

What happens if you forget to update the last node's next pointer when inserting at the end?

A The new node is not linked to the list

B The list becomes circular

C The new node becomes head

D The list deletes the last node

Without updating last node's next pointer, the new node is not connected to the list.

What is the time complexity of inserting at the end of a doubly linked list without a tail pointer?

A O(n^2)

B O(n)

C O(log n)

D O(1)

Without a tail pointer, we must traverse the list to find the end, which takes O(n) time.

Explain step-by-step how to insert a new node at the end of a doubly linked list.

Think about how the pointers connect the nodes forward and backward.

Write a simple Python function to insert a node at the end of a doubly linked list and explain how it works.

Focus on pointer updates and empty list handling.