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

Practice - 5 Tasks

1fill in blank

easy

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

DSA Typescript

this.head = this.head[1];

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

A.next

B.data

C.prev

D.tail

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prev instead of .next to update head.

Trying to assign head to .data which is the node's value, not a node.

When deleting the first node, the head should move to the next node in the list.

2fill in blank

medium

Complete the code to remove the backward link from the new head node.

DSA Typescript

if (this.head) this.head[1] = null;

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

A.prev

B.next

C.head

D.tail

Attempts:

3 left

💡 Hint

Common Mistakes

Setting .next to null instead of .prev.

Trying to set .head or .tail which are not node properties.

After moving head forward, the new head's previous pointer should be null to disconnect from the old node.

3fill in blank

hard

Fix the error in the code that handles the case when the list becomes empty after deletion.

DSA Typescript

if (!this.head) this.[1] = null;

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

Ahead

Bprev

Cnext

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to null again instead of tail.

Trying to set prev or next which are node properties, not list pointers.

If the list is empty after deletion, the tail pointer should also be set to null.

4fill in blank

hard

Fill both blanks to correctly update the list size and return the deleted node's data.

DSA Typescript

this.size[1];
return deletedNode[2];

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

A--

B.data

C.value

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Increasing size instead of decreasing.

Returning the whole node instead of its data.

The size should decrease by one, and the data of the deleted node should be returned.

5fill in blank

hard

Fill all three blanks to complete the deleteFromBeginning method correctly.

DSA Typescript

if (!this.head) return null;
const deletedNode = this.head;
this.head = this.head[1];
if (this.head) this.head[2] = null;
else this.[3] = null;

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

A.next

B.prev

Ctail

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prev instead of .next for head update.

Setting head to null instead of tail when list is empty.

Not clearing the prev pointer of the new head.

The head moves to the next node, the new head's prev is null, and if list is empty, tail is null.

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 previous node

B. It becomes null immediately

C. It stays pointing to the deleted node

D. It moves to the next node in the list

Solution

1. Step 1: Understand the role of head pointer

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

2. Step 2: Effect of deleting the first node

   When the first node is deleted, head must point to the next node to keep the list accessible.

3. Final Answer:

   It moves to the next node in the list -> Option D

4. Quick Check:

   head points to next node after deletion [OK]

Hint: Head always points to the first valid node [OK]

Common Mistakes:

• Setting head to null without checking if list is empty
• Not updating head after deletion
• Pointing head to deleted node

2. Which of the following is the correct TypeScript syntax to delete the first node from a doubly linked list assuming head is the pointer to the first node?

easy

A. head = head.next; head.prev = null;

B. head.prev = null; head = head.next;

C. head.next = null; head = head.prev;

D. head = null; head.next = null;

Solution

1. Step 1: Move head to next node

   Assign head to head.next to remove first node reference.

2. Step 2: Set new head's prev to null

   Set head.prev to null to disconnect backward link from old first node.

3. Final Answer:

   head = head.next; head.prev = null; -> Option A

4. Quick Check:

   Correct syntax to update head and prev pointer [OK]

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

Common Mistakes:

• Setting head.prev before moving head
• Assigning head.prev to null before head changes
• Setting head.next to null incorrectly

3. Given the doubly linked list: 10 <-> 20 <-> 30 <-> null, what will be the list after deleting the first node?

medium

A. 20 <-> 30 <-> null

B. 10 <-> 30 <-> null

C. 30 <-> null

D. null

Solution

1. Step 1: Identify the first node

   The first node is 10, which will be removed.

2. Step 2: Update head to next node

   Head moves to 20, and 20.prev is set to null.

3. Final Answer:

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

4. Quick Check:

   First node removed, list starts at 20 [OK]

Hint: After deletion, list starts from second node [OK]

Common Mistakes:

• Not updating prev pointer of new head
• Removing wrong node
• Leaving old head in list

4. Consider this TypeScript code snippet to delete the first node from a doubly linked list:

if (head !== null) {
  head = head.next;
  head.prev = null;
}

What error can occur here?

medium

A. Logical error: head.prev should not be set to null

B. Syntax error due to missing semicolon

C. Runtime error if list has only one node

D. No error, code is correct

Solution

1. Step 1: Check condition when list has one node

   If list has one node, head.next is null after deletion.

2. Step 2: Accessing head.prev causes error

   head becomes null, so head.prev causes runtime error (cannot access property of null).

3. Final Answer:

   Runtime error if list has only one node -> Option C

4. Quick Check:

   Null pointer access error possible [OK]

Hint: Check if head is null before accessing head.prev [OK]

Common Mistakes:

• Not checking if head is null after moving to next
• Assuming list always has multiple nodes
• Ignoring runtime null errors

5. You have a doubly linked list with nodes: 5 <-> 15 <-> 25 <-> 35 <-> null. Write the correct sequence of operations to delete the first node safely, considering the list might have only one node.

hard

A. head.prev = null; head = head.next;

B. if (head !== null) { head = head.next; if (head !== null) head.prev = null; }

C. if (head.next !== null) { head = head.next; head.prev = null; }

D. head = head.next; head.prev = null;

Solution

1. Step 1: Check if list is empty

   First, verify head is not null to avoid errors on empty list.

2. Step 2: Move head to next node and check again

   After moving head, check if new head is not null before setting prev to null.

3. Final Answer:

   if (head !== null) { head = head.next; if (head !== null) head.prev = null; } -> Option B

4. Quick Check:

   Safe deletion with null checks [OK]

Hint: Always check for null before accessing pointers [OK]

Common Mistakes:

• Not checking if head is null after moving
• Setting prev pointer without null check
• Assuming list has multiple nodes always