Delete by Value in Doubly Linked List in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the list is empty before deletion.

DSA Javascript

if (this.head === [1]) {
  return;
}

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

Aundefined

B0

Cfalse

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined instead of null

Checking for 0 or false which are not valid for empty list

We check if this.head is null to see if the list is empty.

2fill in blank

medium

Complete the code to move to the next node in the list during traversal.

DSA Javascript

while (current !== null && current.data !== value) {
  current = current[1];
}

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

A.tail

B.prev

C.next

D.head

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prev which moves backward

Using .head or .tail which are properties of the list, not nodes

We move to the next node by using current.next.

3fill in blank

hard

Fix the error in updating the previous node's next pointer after deletion.

DSA Javascript

if (current.prev !== null) {
  current.prev[1] = current.next;
}

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

A.next

B.tail

C.head

D.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Using .prev instead of .next causing incorrect links

Using .head or .tail which are not node properties

We update current.prev.next to skip the deleted node.

4fill in blank

hard

Fill both blanks to correctly update the next node's previous pointer and handle head deletion.

DSA Javascript

if (current.next !== null) {
  current.next[1] = current.prev;
} else {
  this.[2] = current.prev;
}

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

A.prev

B.next

Ctail

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping .prev and .next in the first blank

Updating this.head instead of this.tail when deleting the last node

The next node's previous pointer is updated to current's previous node. If current is the tail, update this.tail.

5fill in blank

hard

Fill all three blanks to handle deletion when current is the head node and update the head pointer.

DSA Javascript

if (current === this.[1]) {
  this.[2] = current.next;
  if (this.[3] !== null) {
    this.[3].prev = null;
  }
}

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

Ahead

Btail

Attempts:

3 left

💡 Hint

Common Mistakes

Using tail instead of head for the first blank

Not setting the new head's prev to null

If current is the head, update this.head to the next node and set the new head's previous pointer to null.

Practice

1. What happens when you delete a node by value in a doubly linked list?

easy

A. The node with the matching value is removed and links are updated

B. All nodes are deleted regardless of value

C. Only the first node is deleted no matter the value

D. The list is reversed instead of deleting

Solution

1. Step 1: Locate the node with the given value

   Traverse the list from head to tail to find the node whose value matches the target.

2. Step 2: Remove the node and update links

   Adjust the previous node's next pointer and the next node's previous pointer to bypass the deleted node.

3. Final Answer:

   The node with the matching value is removed and links are updated -> Option A

4. Quick Check:

   Delete by value means remove matching node [OK]

Hint: Delete node by value means remove matching node and fix links [OK]

Common Mistakes:

• Deleting all nodes instead of one
• Not updating previous or next pointers
• Deleting wrong node when multiple have same value

2. Which of the following is the correct way to check if the current node's value matches the target value in JavaScript?

easy

A. if (current.value != target) {}

B. if (current.value == target) {}

C. if (current.value = target) {}

D. if (current.value === target) {}

Solution

1. Step 1: Understand JavaScript equality operators

   Use === for strict equality to avoid type coercion and ensure exact match.

2. Step 2: Identify correct syntax for comparison

   if (current.value === target) correctly compares values and types.

3. Final Answer:

   if (current.value === target) {} -> Option D

4. Quick Check:

   Use strict equality (===) for value comparison [OK]

Hint: Use === for exact value and type match in JavaScript [OK]

Common Mistakes:

• Using single = which assigns instead of compares
• Using == which allows type coercion
• Using != which checks inequality

3. Consider this doubly linked list: 10 <-> 20 <-> 30 <-> 40. After deleting the node with value 30, what is the new list?

medium

A. 10 <-> 20 <-> 30 <-> 40

B. 10 <-> 20 <-> 40

C. 20 <-> 30 <-> 40

D. 10 <-> 30 <-> 40

Solution

1. Step 1: Identify node to delete

   The node with value 30 is located between 20 and 40.

2. Step 2: Remove node 30 and update links

   Set 20's next pointer to 40 and 40's previous pointer to 20, skipping 30.

3. Final Answer:

   10 <-> 20 <-> 40 -> Option B

4. Quick Check:

   Deleted 30, linked 20 and 40 directly [OK]

Hint: Remove node and link neighbors directly [OK]

Common Mistakes:

• Not updating previous pointer of next node
• Leaving deleted node linked in list
• Deleting wrong node

4. Given this code snippet to delete a node by value, what is the error?

function deleteByValue(head, value) {
  let current = head;
  while (current !== null) {
    if (current.value === value) {
      current.prev.next = current.next;
      current.next.prev = current.prev;
      break;
    }
    current = current.next;
  }
  return head;
}

medium

A. It uses assignment instead of comparison

B. It never breaks the loop

C. It does not handle deleting the head node correctly

D. It returns null always

Solution

1. Step 1: Analyze deletion of head node

   If the node to delete is the head, current.prev is null, so current.prev.next causes error.

2. Step 2: Identify missing head update

   Code should update head to current.next if deleting head node to avoid broken list.

3. Final Answer:

   It does not handle deleting the head node correctly -> Option C

4. Quick Check:

   Deleting head needs special handling [OK]

Hint: Check if node is head before updating prev pointers [OK]

Common Mistakes:

• Not checking if current.prev is null
• Not updating head when deleting first node
• Assuming all nodes have prev and next

5. You have a doubly linked list: 5 <-> 10 <-> 15 <-> 20 <-> 25. You want to delete the node with value 5 (head) and then the node with value 25 (tail). What is the final list?

hard

A. 10 <-> 15 <-> 20

B. 5 <-> 10 <-> 15 <-> 20

C. 10 <-> 15 <-> 20 <-> 25

D. 15 <-> 20

Solution

1. Step 1: Delete head node with value 5

   Update head to 10 and set 10.prev to null.

2. Step 2: Delete tail node with value 25

   Update 20.next to null, removing 25.

3. Final Answer:

   10 <-> 15 <-> 20 -> Option A

4. Quick Check:

   Removed head and tail nodes correctly [OK]

Hint: Update head or tail pointers when deleting ends [OK]

Common Mistakes:

• Not updating head when deleting first node
• Not updating tail when deleting last node
• Leaving dangling pointers