Reverse a Doubly Linked List in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap the next and prev pointers of the current node.

DSA Python

current.next, current.prev = current.prev, [1]

Drag options to blanks, or click blank then click option'

Acurrent.prev

Bcurrent.next

Chead

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning current.next to current.next instead of current.prev.

Using head or None instead of current.prev.

Swapping current.next and current.prev requires assigning current.prev to current.next and current.next to current.prev. Here, current.next is assigned to current.prev.

2fill in blank

medium

Complete the code to move to the next node in the original list during reversal.

DSA Python

current = [1]

Drag options to blanks, or click blank then click option'

Acurrent.prev

Bcurrent.next

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using current.next which now points backward after swapping.

Using head or tail instead of moving current.

After swapping next and prev, the original next node is now current.prev, so we move current to current.prev.

3fill in blank

hard

Fix the error in updating the head pointer after reversal.

DSA Python

if current is None:
    head = [1]

Drag options to blanks, or click blank then click option'

Ahead

Bcurrent

Cprev

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to current which is None.

Assigning head to tail or head itself.

When current becomes None, prev points to the new head of the reversed list, so head should be updated to prev.

4fill in blank

hard

Fill both blanks to complete the reversal loop and update pointers correctly.

DSA Python

while current is not None:
    current.next, current.prev = current.prev, current.next
    prev = [1]
    current = [2]

Drag options to blanks, or click blank then click option'

Acurrent

Bprev

Ccurrent.prev

Dcurrent.next

Attempts:

3 left

💡 Hint

Common Mistakes

Updating prev to prev or current.next incorrectly.

Moving current to current.next which is swapped.

Inside the loop, prev is updated to current before moving current to current.prev (the original next node after swapping).

5fill in blank

hard

Fill all three blanks to create a function that reverses a doubly linked list and returns the new head.

DSA Python

def reverse_doubly_linked_list(head):
    current = head
    prev = None
    while current is not None:
        current.next, current.prev = current.prev, current.next
        prev = [1]
        current = [2]
    if current is None:
        head = [3]
    return head

Drag options to blanks, or click blank then click option'

Acurrent

Bcurrent.prev

Cprev

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using current.next instead of current.prev for moving current.

Not updating head to prev after reversal.

Assigning prev incorrectly inside the loop.

Inside the loop, prev is updated to current, current moves to current.prev (original next), and after loop, head is updated to prev.