Delete from Beginning 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 traversal in both directions.

beginner

What happens when you delete the first node in a doubly linked list?

The head pointer moves to the second node, and the new head's previous pointer is set to None. The old first node is removed from the list.

intermediate

Why do we need to update the previous pointer of the new head to null after deletion?

Because the new head is now the first node, it should not point back to any node. Setting its previous pointer to None ensures the list starts correctly.

beginner

What should you check before deleting the first node in a doubly linked list?

You should check if the list is empty (head is None). If it is empty, there is nothing to delete.

intermediate

Show the Python code snippet to delete the first node from a doubly linked list.

def delete_from_beginning(head): if head is None: return None new_head = head.next if new_head is not None: new_head.prev = None return new_head

What pointer must be updated when deleting the first node in a doubly linked list?

A The next pointer of the new head

B The previous pointer of the new head

C The data pointer of the first node

D The next pointer of the last node

After deletion, the new head's previous pointer must be set to None to mark it as the first node.

What should happen if the doubly linked list is empty and you try to delete from the beginning?

A Delete the last node

B Throw an error

C Return the list as is (None head)

D Create a new node

If the list is empty (head is None), deletion does nothing and returns None.

After deleting the first node, what becomes the new head of the doubly linked list?

A The last node

B A new empty node

C The deleted node

D The second node

The second node becomes the new head after the first node is deleted.

Which of these is NOT a part of a doubly linked list node?

A Pointer to random node

B Pointer to next node

C Data

D Pointer to previous node

A standard doubly linked list node has data, next pointer, and previous pointer, but not a random pointer.

What is the time complexity of deleting the first node in a doubly linked list?

A O(1)

B O(n)

C O(log n)

D O(n^2)

Deleting the first node is a constant time operation because it involves updating only a few pointers.

Explain step-by-step how to delete the first node from a doubly linked list.

Think about what pointers need to change and what happens if the list is empty.

Write a simple Python function to delete the first node of a doubly linked list and return the new head.

Focus on pointer updates and edge cases.