Delete Node at Specific Position in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Delete Node at Specific Position' mean in a linked list?

It means removing the node that is at a given position (like 1st, 2nd, 3rd) from the linked list, and then connecting the previous node to the next node to keep the list linked.

beginner

Why do we need to handle the first node (head) differently when deleting at a specific position?

Because the head is the start of the list, deleting it means the head must point to the next node. We can't just skip it like other nodes.

beginner

In JavaScript, how do you move to the node just before the one you want to delete?

You start from the head and move forward one node at a time until you reach the node at position (pos - 1).

beginner

What happens if you try to delete a node at a position greater than the list length?

Nothing changes because the position is invalid. The list stays the same.

intermediate

What is the time complexity of deleting a node at a specific position in a singly linked list?

It is O(n) because you may need to traverse up to n nodes to reach the position before the node to delete.

What should you do first when deleting the head node of a linked list?

A Make the head point to the next node

B Find the last node

C Swap the head with the last node

D Do nothing

When deleting the head, you update the head pointer to the next node to remove the first node.

If you want to delete the node at position 3, which node do you need to reach first?

A Node at position 1

B Node at position 2

C Node at position 3

D Node at position 4

You need to reach the node before the one to delete, which is position 2.

What happens if the position to delete is 1 in a linked list?

A Delete the head node

B Delete the middle node

C Delete the last node

D No deletion

Position 1 means the head node, so deleting position 1 deletes the head.

What is the main challenge when deleting a node in the middle of a singly linked list?

A Creating a new node

B Finding the last node

C Changing the node's value

D Finding the node before the one to delete

You must find the node before the one to delete to change its next pointer.

If the position to delete is greater than the length of the list, what should happen?

A Delete the last node

B Delete the head node

C No change to the list

D Delete a random node

Deleting a node at an invalid position should not change the list.

Explain step-by-step how to delete a node at a specific position in a singly linked list.

Think about how you move through the list and update links.

Describe how deleting the head node differs from deleting a node in the middle of the list.

Focus on what pointers you change.

Practice

1. What happens when you delete a node at position 0 in a singly linked list?

easy

A. The head pointer moves to the next node, effectively removing the first node.

B. The last node is removed from the list.

C. The list becomes empty regardless of its size.

D. The node at position 1 is deleted instead.

Solution

1. Step 1: Understand position 0 in linked list

   Position 0 refers to the first node, also called the head.

2. Step 2: Effect of deleting head node

   Deleting the head means moving the head pointer to the next node, removing the first node from the list.

3. Final Answer:

   The head pointer moves to the next node, effectively removing the first node. -> Option A

4. Quick Check:

   Deleting position 0 removes the first node [OK]

Hint: Deleting position 0 means changing the head pointer [OK]

Common Mistakes:

• Thinking the last node is deleted instead
• Assuming the list becomes empty always
• Deleting the wrong node position

2. Which of the following is the correct syntax to delete a node at position pos in a singly linked list in JavaScript?

easy

A. head = head[pos + 1];

B. if (pos === 0) head = head.next;

C. delete head[pos];

D. head.next = null;

Solution

1. Step 1: Check deletion at position 0

   Deleting at position 0 means moving head to head.next.

2. Step 2: Validate syntax correctness

   if (pos === 0) head = head.next; correctly assigns head to head.next. Other options misuse syntax or do not delete the node properly.

3. Final Answer:

   if (pos === 0) head = head.next; -> Option B

4. Quick Check:

   Correct syntax for deleting head node is head = head.next [OK]

Hint: To delete head, assign head = head.next [OK]

Common Mistakes:

• Using delete keyword incorrectly on linked list nodes
• Assigning head.next to null without updating head
• Accessing nodes with array-like syntax

3. Given the linked list: 10 -> 20 -> 30 -> 40 -> null, what is the list after deleting the node at position 2?

medium

A. 10 -> 20 -> 30 -> null

B. 10 -> 30 -> 40 -> null

C. 20 -> 30 -> 40 -> null

D. 10 -> 20 -> 40 -> null

Solution

1. Step 1: Identify node at position 2

   Positions start at 0, so position 2 is the third node with value 30.

2. Step 2: Delete node at position 2

   Remove node 30 by linking node 20's next to node 40.

3. Final Answer:

   10 -> 20 -> 40 -> null -> Option D

4. Quick Check:

   Deleted node 30 at position 2 [OK]

Hint: Count from 0, remove node at that index [OK]

Common Mistakes:

• Deleting wrong node by miscounting positions
• Not updating the previous node's next pointer
• Confusing node values with positions

4. What is the error in the following code snippet for deleting a node at position pos in a singly linked list?

function deleteNode(head, pos) {
  let current = head;
  for (let i = 0; i < pos - 1; i++) {
    current = current.next;
  }
  current.next = current.next.next;
  return head;
}

medium

A. It does not handle deletion when pos is 0 (head node).

B. It incorrectly updates the head pointer.

C. It causes a syntax error due to missing semicolons.

D. It deletes the last node instead of the specified position.

Solution

1. Step 1: Analyze loop for position traversal

   The loop stops at node before position to delete, which is correct for pos > 0.

2. Step 2: Check handling of pos = 0

   When pos is 0, the loop does not run and current is head, but code does not update head pointer, so deletion fails.

3. Final Answer:

   It does not handle deletion when pos is 0 (head node). -> Option A

4. Quick Check:

   Missing head deletion case causes error [OK]

Hint: Always check if deleting head node separately [OK]

Common Mistakes:

• Ignoring edge case when pos is 0
• Assuming loop handles all positions
• Not updating head pointer when needed

5. You have a singly linked list: 5 -> 15 -> 25 -> 35 -> 45 -> null. You want to delete the node at position 4. What will the list look like after deletion? Also, what happens if you try to delete at position 5?

hard

A. After deletion at position 4: 5 -> 15 -> 25 -> 35 -> null; Deleting position 5 causes a runtime error.

B. After deletion at position 4: 5 -> 15 -> 25 -> 35 -> 45 -> null; Deleting position 5 removes the last node.

C. After deletion at position 4: 5 -> 15 -> 25 -> 35 -> null; Deleting position 5 does nothing as it's out of range.

D. After deletion at position 4: 15 -> 25 -> 35 -> 45 -> null; Deleting position 5 removes the head.

Solution

1. Step 1: Identify node at position 4

   Positions start at 0, so position 4 is the fifth node with value 45.

2. Step 2: Delete node at position 4

   Remove node 45 by linking node 35's next to null.

3. Step 3: Consider deletion at position 5

   Position 5 is out of list range (list length is 5), so deletion does nothing safely.

4. Final Answer:

   After deletion at position 4: 5 -> 15 -> 25 -> 35 -> null; Deleting position 5 does nothing as it's out of range. -> Option C

5. Quick Check:

   Deleting last node removes it; out-of-range deletion ignored [OK]

Hint: Deleting out-of-range position does nothing [OK]

Common Mistakes:

• Trying to delete non-existent node causing errors
• Confusing positions and node values
• Not updating previous node's next pointer correctly