Delete Node by Value in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Delete Node by Value' mean in a linked list?

It means finding a node with a specific value in the linked list and removing it, so the list no longer contains that node.

beginner

Why do we need to keep track of the previous node when deleting a node by value?

Because to remove a node, we must change the 'next' pointer of the previous node to skip the node being deleted and point to the next node instead.

beginner

What happens if the node to delete is the head of the linked list?

We update the head pointer to point to the next node, effectively removing the original head from the list.

beginner

In JavaScript, how can you check if a node with a given value exists before deleting?

You can traverse the list from the head, comparing each node's value to the target value until you find it or reach the end.

beginner

What should happen if the value to delete is not found in the linked list?

The list remains unchanged because there is no node with that value to remove.

What is the first step when deleting a node by value in a linked list?

A Create a new node

B Delete the head node immediately

C Traverse the list to find the node with the value

D Reverse the linked list

You must first find the node with the target value before deleting it.

If the node to delete is the head, what should you do?

A Set head to the next node

B Do nothing

C Delete the last node

D Set head to null

The head pointer should be updated to the next node to remove the current head.

Why do we keep track of the previous node during deletion?

A To reverse the list

B To print the list

C To add a new node

D To update the previous node's next pointer

We update the previous node's next pointer to skip the deleted node.

What happens if the value to delete is not found?

A The list is cleared

B The list remains unchanged

C The last node is deleted

D The head is deleted

No node matches the value, so the list stays the same.

Which pointer changes when deleting a node in the middle of the list?

A The previous node's next pointer

B The deleted node's next pointer

C The head pointer

D The tail pointer

The previous node's next pointer is updated to skip the deleted node.

Explain step-by-step how to delete a node by value in a singly linked list.

Think about how you move through the list and change pointers.

What special cases must you consider when deleting a node by value in a linked list?

Consider where the node is located and if it exists.

Practice

1. What is the main purpose of the deleteNodeByValue function in a linked list?

easy

A. To reverse the linked list

B. To add a new node with the given value at the end of the list

C. To find the position of a node with the given value

D. To remove the first node that contains the given value from the list

Solution

1. Step 1: Understand the function's goal

   The function aims to remove a node that matches a specific value from the linked list.

2. Step 2: Identify the action performed

   Deleting a node by value means finding the first node with that value and removing it from the list.

3. Final Answer:

   To remove the first node that contains the given value from the list -> Option D

4. Quick Check:

   Delete node by value = Remove node with value [OK]

Hint: Deleting by value means removing matching node, not adding [OK]

Common Mistakes:

• Confusing deletion with insertion
• Thinking it finds position only
• Assuming it reverses the list

2. Which of the following is the correct way to check if the head node contains the value to delete in JavaScript?

easy

A. if (head.value === value) { /* delete head */ }

B. if (head == value) { /* delete head */ }

C. if (head.value = value) { /* delete head */ }

D. if (head.value != value) { /* delete head */ }

Solution

1. Step 1: Understand comparison syntax in JavaScript

   Use triple equals (===) to compare values strictly without type coercion.

2. Step 2: Identify correct condition for head node value check

   Check if head.value equals the target value using ===.

3. Final Answer:

   if (head.value === value) { /* delete head */ } -> Option A

4. Quick Check:

   Use === for value comparison [OK]

Hint: Use === to compare values, not = or == [OK]

Common Mistakes:

• Using single = which assigns instead of compares
• Using == which can cause unexpected type coercion
• Comparing head node directly to value without .value

3. Consider the linked list: 10 -> 20 -> 30 -> 40 -> null. After calling deleteNodeByValue(head, 30), what will be the new list?

medium

A. 20 -> 30 -> 40 -> null

B. 10 -> 20 -> 30 -> 40 -> null

C. 10 -> 20 -> 40 -> null

D. 10 -> 30 -> 40 -> null

Solution

1. Step 1: Locate the node with value 30

   Traverse the list: 10, 20, then 30 is found as the third node.

2. Step 2: Remove the node with value 30

   Adjust the previous node's next pointer (20's next) to point to 40, skipping 30.

3. Final Answer:

   10 -> 20 -> 40 -> null -> Option C

4. Quick Check:

   Deleted 30 node, list skips it [OK]

Hint: Skip node by linking previous to next [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Deleting wrong node or none
• Confusing node values or order

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

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

medium

A. It causes an infinite loop when value is not found

B. It does not handle deleting the head node if it matches the value

C. It deletes all nodes with the given value instead of just one

D. It throws an error if the list is empty

Solution

1. Step 1: Analyze head node deletion case

   The code starts checking from current.next, so it never checks if head itself has the value.

2. Step 2: Identify missing head deletion handling

   If the head node contains the value, it won't be deleted, causing incorrect behavior.

3. Final Answer:

   It does not handle deleting the head node if it matches the value -> Option B

4. Quick Check:

   Head node deletion missing = Bug [OK]

Hint: Always check head node separately before loop [OK]

Common Mistakes:

• Assuming loop covers head node
• Ignoring empty list case
• Thinking it deletes all matching nodes

5. You have a singly linked list: 5 -> 10 -> 15 -> 10 -> 20 -> null. You want to delete the first node with value 10. After deletion, what is the correct list?

hard

A. 5 -> 15 -> 10 -> 20 -> null

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

C. 5 -> 15 -> 20 -> null

D. 10 -> 15 -> 10 -> 20 -> null

Solution

1. Step 1: Identify the first node with value 10

   Traverse from head: 5 (no), then 10 (yes) at second node.

2. Step 2: Delete the first 10 node

   Link 5's next pointer to 15, skipping the first 10 node.

3. Final Answer:

   5 -> 15 -> 10 -> 20 -> null -> Option A

4. Quick Check:

   Only first 10 removed, rest remain [OK]

Hint: Delete first matching node only, keep others [OK]

Common Mistakes:

• Deleting all nodes with value 10
• Deleting wrong 10 node
• Breaking list links incorrectly