Delete from Beginning of Doubly Linked List in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the head pointer after deleting the first node.

DSA Python

def delete_from_beginning(head):
    if head is None:
        return None
    new_head = head.[1]
    if new_head is not None:
        new_head.prev = None
    return new_head

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

Anext

Bprev

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to update the head.

Not updating the head pointer at all.

After deleting the first node, the new head should be the next node in the list, which is accessed by head.next.

2fill in blank

medium

Complete the code to set the previous pointer of the new head to None.

DSA Python

def delete_from_beginning(head):
    if head is None:
        return None
    new_head = head.next
    if new_head is not None:
        new_head.[1] = None
    return new_head

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

Aprev

Bnext

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the next pointer to None instead of the previous pointer.

Forgetting to update the previous pointer.

The previous pointer of the new head should be set to None because it becomes the first node.

3fill in blank

hard

Fix the error in the code to correctly delete the first node of the doubly linked list.

DSA Python

def delete_from_beginning(head):
    if head is None:
        return None
    temp = head
    head = head.[1]
    if head is not None:
        head.prev = None
    del temp
    return head

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

Ahead

Bnext

Cdata

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to update the head.

Deleting the wrong node.

The head should be updated to head.next to move to the next node after deletion.

4fill in blank

hard

Fill both blanks to complete the function that deletes the first node and returns the updated head.

DSA Python

def delete_from_beginning(head):
    if head is None:
        return None
    temp = head
    head = head.[1]
    if head is not None:
        head.[2] = None
    del temp
    return head

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

Anext

Bprev

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping 'next' and 'prev' in the blanks.

Not deleting the old head node.

First, update the head to head.next. Then set the new head's previous pointer to None.

5fill in blank

hard

Fill all three blanks to complete the function that deletes the first node and returns the updated head.

DSA Python

def delete_from_beginning(head):
    if head is None:
        return None
    temp = head
    head = head.[1]
    if head is not None:
        head.[2] = None
    del [3]
    return head

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

Anext

Bprev

Ctemp

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to delete the old head node.

Using wrong variable names in deletion.

Update head to head.next, set head.prev to None, and delete the old head stored in temp.

Practice

1. What happens to the head pointer when you delete the first node from a doubly linked list?

easy

A. It moves to the second node in the list

B. It becomes null immediately

C. It points to the last node in the list

D. It remains pointing to the deleted node

Solution

1. Step 1: Understand the head pointer role

   The head pointer always points to the first node in the list.

2. Step 2: After deleting the first node

   The head must move to the next node, which becomes the new first node.

3. Final Answer:

   It moves to the second node in the list -> Option A

4. Quick Check:

   Head points to new first node after deletion [OK]

Hint: Head always points to the first node, update after deletion [OK]

Common Mistakes:

• Not updating head pointer after deletion
• Setting head to null even if list has more nodes
• Leaving head pointing to deleted node

2. Which of the following is the correct syntax to delete the first node in a doubly linked list in Python?

easy

A. head = None; head.next = None

B. head.prev = None; head = head.next

C. head = head.next; head.prev = None

D. head.next = None; head = head.prev

Solution

1. Step 1: Move head to next node

   Assign head = head.next to move head forward.

2. Step 2: Remove backward link

   Set head.prev = None to disconnect previous first node.

3. Final Answer:

   head = head.next; head.prev = None -> Option C

4. Quick Check:

   Update head then clear prev link [OK]

Hint: Update head first, then clear prev pointer [OK]

Common Mistakes:

• Setting prev before moving head
• Trying to set next of head to None incorrectly
• Setting head to None without updating

3. What will be the output linked list after deleting the first node from this doubly linked list?

Initial list: 10 <-> 20 <-> 30 <-> null

Code snippet:

head = head.next
head.prev = None

medium

A. 20 <-> 30 <-> null

B. 10 <-> 30 <-> null

C. 30 <-> null

D. null

Solution

1. Step 1: Move head to second node

   Head moves from 10 to 20.

2. Step 2: Remove backward link of new head

   Set 20.prev = None, disconnecting 10.

3. Final Answer:

   20 <-> 30 <-> null -> Option A

4. Quick Check:

   First node removed, list starts at 20 [OK]

Hint: After deletion, head points to second node [OK]

Common Mistakes:

• Forgetting to set prev to None
• Incorrectly skipping nodes
• Outputting original list without change

4. Identify the error in this code snippet for deleting the first node of a doubly linked list:

if head is not None:
    head = head.next
    head.prev = None

medium

A. No error, code is correct

B. head.prev = None causes error if head.next is None

C. head = head.next should be after setting prev to None

D. Missing deletion of the old head node

Solution

1. Step 1: Check head.next for None

   If head.next is None, head becomes None after assignment.

2. Step 2: Setting head.prev causes error

   Trying to set head.prev = None when head is None causes AttributeError.

3. Final Answer:

   head.prev = None causes error if head.next is None -> Option B

4. Quick Check:

   Check for None before setting prev [OK]

Hint: Check if head is None before setting head.prev [OK]

Common Mistakes:

• Not checking if head.next is None
• Assuming list has more than one node always
• Ignoring possible AttributeError

5. Given a doubly linked list with nodes: 5 <-> 15 <-> 25 <-> 35 <-> null, after deleting the first node twice, what will be the resulting list?

hard

A. null

B. 15 <-> 25 <-> 35 <-> null

C. 35 <-> null

D. 25 <-> 35 <-> null

Solution

1. Step 1: First deletion moves head from 5 to 15

   After first deletion, list is 15 <-> 25 <-> 35 <-> null.

2. Step 2: Second deletion moves head from 15 to 25

   After second deletion, list is 25 <-> 35 <-> null.

3. Final Answer:

   25 <-> 35 <-> null -> Option D

4. Quick Check:

   Two deletions remove first two nodes [OK]

Hint: Each deletion moves head to next node [OK]

Common Mistakes:

• Deleting only once instead of twice
• Not updating head correctly after each deletion
• Confusing node values or order