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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the tail pointer after deleting the last node.

DSA Typescript

this.tail = this.tail[1];

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

Aprev

Bnext

Chead

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting tail to next causes tail to become null or incorrect.

Setting tail to head does not update tail correctly.

After deleting the last node, the tail should point to the previous node.

2fill in blank

medium

Complete the code to remove the last node's reference to the list.

DSA Typescript

if (this.tail) this.tail.next = [1];

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

Anull

Bthis.head

Cthis.tail

Dthis.tail.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to this.tail creates a cycle.

Setting next to this.head breaks the list structure.

After deletion, the new tail's next pointer should be null to mark the end.

3fill in blank

hard

Fix the error in the condition that checks if the list is empty after deletion.

DSA Typescript

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

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

Athis.tail.prev

Bthis.head

Cundefined

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing tail to head is incorrect for empty check.

Using undefined instead of null may cause unexpected behavior.

If tail is null, the list is empty, so head should also be null.

4fill in blank

hard

Fill both blanks to correctly update pointers when deleting the last node.

DSA Typescript

if (this.tail) {
  this.tail.next = [1];
  this.tail = this.tail[2];
}

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

Anull

Bprev

Cnext

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to next instead of null.

Moving tail to next instead of prev.

The new tail's next pointer should be null, and tail moves to its previous node.

5fill in blank

hard

Fill all three blanks to complete the delete from end method correctly.

DSA Typescript

deleteFromEnd() {
  if (!this.tail) return null;
  const removed = this.tail;
  if (this.tail === this.head) {
    this.head = [1];
    this.tail = [2];
  } else {
    this.tail = this.tail[3];
    if (this.tail) this.tail.next = null;
  }
  return removed;
}

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

Anull

Cprev

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Setting tail to next instead of prev.

Not setting head to null when list becomes empty.

If the list has one node, both head and tail become null after deletion. Otherwise, tail moves to previous node.

Practice

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

easy

A. It becomes null immediately

B. It moves to the previous node of the deleted node

C. It points to the head node

D. It remains unchanged

Solution

1. Step 1: Understand the tail pointer role

   The tail pointer always points to the last node in the list.

2. Step 2: Effect of deleting the last node

   When the last node is deleted, the tail must move to the previous node to remain the last node.

3. Final Answer:

   It moves to the previous node of the deleted node -> Option B

4. Quick Check:

   Tail updates to previous node after deletion [OK]

Hint: Tail always points to last node, so move it back after deletion [OK]

Common Mistakes:

• Setting tail to null without checking if list is empty
• Not updating tail pointer after deletion
• Confusing head and tail pointers
• Assuming tail points to head after deletion

2. Which of the following is the correct TypeScript syntax to delete the last node from a doubly linked list assuming tail is not null?

easy

A. tail = tail.prev; tail.next = null;

B. tail = tail.next; tail.prev = null;

C. tail = null; head = null;

D. tail.prev = tail; tail.next = null;

Solution

1. Step 1: Move tail pointer to previous node

   To delete the last node, tail must point to its previous node: tail = tail.prev;

2. Step 2: Set new tail's next to null

   Since tail is now last node, its next must be null: tail.next = null;

3. Final Answer:

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

4. Quick Check:

   Correct syntax moves tail back and nullifies next [OK]

Hint: Tail moves back, then tail.next set to null [OK]

Common Mistakes:

• Moving tail forward instead of backward
• Not setting tail.next to null
• Setting tail to null without updating links
• Confusing prev and next pointers

3. Given the doubly linked list: 1 <-> 2 <-> 3 <-> 4 <-> null, what is the list after deleting the last node?

medium

A. 1 <-> 2 <-> 3 <-> null

B. 1 <-> 2 <-> 3 <-> 4 <-> null

C. 2 <-> 3 <-> 4 <-> null

D. 1 <-> 2 <-> null

Solution

1. Step 1: Identify the last node

   The last node is 4, pointed by tail.

2. Step 2: Delete last node and update tail

   Remove node 4, update tail to node 3, set tail.next to null.

3. Final Answer:

   1 <-> 2 <-> 3 <-> null -> Option A

4. Quick Check:

   Last node 4 removed, tail now 3 [OK]

Hint: Remove last node, tail moves to previous node [OK]

Common Mistakes:

• Not updating tail pointer
• Leaving deleted node linked
• Removing wrong node
• Confusing head and tail updates

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

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

What error can occur here?

medium

A. No error, code is correct

B. Syntax error due to missing semicolon

C. Runtime error if list has only one node

D. Tail pointer moves forward incorrectly

Solution

1. Step 1: Analyze single-node list case

   If list has one node, tail.prev is null, so tail becomes null.

2. Step 2: Accessing tail.next causes error

   After tail = tail.prev (null), next line tries tail.next = null, causing runtime error (cannot access property of null).

3. Final Answer:

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

4. Quick Check:

   Null tail causes runtime error on next access [OK]

Hint: Check if tail.prev is null before setting tail.next [OK]

Common Mistakes:

• Not handling single-node list edge case
• Assuming tail is never null after update
• Ignoring runtime null pointer errors
• Confusing syntax errors with runtime errors

5. You have a doubly linked list with nodes: 10 <-> 20 <-> 30. After deleting the last node twice, what is the final list?

hard

A. 10 <-> 20 <-> null

B. 20 <-> null

C. null

D. 10 <-> null

Solution

1. Step 1: Delete last node first time

   Last node 30 is removed, tail moves to 20, list becomes 10 <-> 20 <-> null.

2. Step 2: Delete last node second time

   Last node 20 is removed, tail moves to 10, list becomes 10 <-> null.

3. Step 3: Verify final list

   After two deletions, list is 10 <-> null.

4. Final Answer:

   10 <-> null -> Option D

5. Quick Check:

   Two deletions remove 30 and 20, leaving 10 [OK]

Hint: Delete last node twice removes last two nodes [OK]

Common Mistakes:

• Deleting only one node instead of two
• Confusing node values after deletion
• Not updating tail pointer correctly
• Assuming list becomes empty too early