Delete Node by Value in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Typescript

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

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

Afalse

Bnull

C0

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for undefined instead of null.

Using 0 or false which are not valid for empty list.

The head of the list is null when the list is empty, so we check if this.head === null.

2fill in blank

medium

Complete the code to delete the head node if it matches the value.

DSA Typescript

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

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

Avalue

Btarget

Cval

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong variable name like value or node.

Comparing with this.value instead of val.

We compare the head node's value with the given val to decide deletion.

3fill in blank

hard

Fix the error in the while loop condition to traverse the list correctly.

DSA Typescript

while (current.next !== [1]) {
  if (current.next.value === val) {
    current.next = current.next.next;
    return;
  }
  current = current.next;
}

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

Afalse

Bundefined

C0

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined or false which do not mark list end.

Using 0 which is not a valid node reference.

We check if current.next is not null to continue traversing the list.

4fill in blank

hard

Fill both blanks to correctly initialize and traverse the linked list for deletion.

DSA Typescript

let current = this.[1];
while (current.[2] !== null) {
  if (current.next.value === val) {
    current.next = current.next.next;
    return;
  }
  current = current.next;
}

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

Ahead

Btail

Cnext

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from tail which is the end of the list.

Using prev which is for doubly linked lists.

We start from the head and traverse using the next pointer to find the node to delete.

5fill in blank

hard

Fill all three blanks to complete the deleteNodeByValue method correctly.

DSA Typescript

deleteNodeByValue(val: number): void {
  if (this.head === [1]) {
    return;
  }
  if (this.head.value === val) {
    this.head = this.head.[2];
    return;
  }
  let current = this.head;
  while (current.next !== [3]) {
    if (current.next.value === val) {
      current.next = current.next.next;
      return;
    }
    current = current.next;
  }
}

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

Anull

Bnext

Cundefined

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined instead of null.

Using head instead of next to update pointers.

We check if head is null, update head to head.next if head matches val, and traverse while current.next is not null.

Practice

1. What is the main purpose of the Delete Node by Value operation in a linked list?

easy

A. Reverse the linked list

B. Add a new node with the given value at the end

C. Remove the first node that contains the given value

D. Find the position of a node with the given value

Solution

1. Step 1: Understand the operation goal

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

2. Step 2: Identify the correct action

   Removing the first node with the given value means deleting that node and linking its previous node to the next node.

3. Final Answer:

   Remove the first node that contains the given value -> Option C

4. Quick Check:

   Delete node by value = Remove first matching node [OK]

Hint: Delete node by value means remove first matching node [OK]

Common Mistakes:

• Confusing deletion with insertion
• Trying to delete all nodes with the value instead of first
• Thinking it finds position only
• Assuming it reverses the list

2. Which of the following TypeScript code snippets correctly deletes the head node if its value is 5 from a singly linked list starting at head?

easy

A. if (head.value === 5) head = head.next;

B. head = head.next.value === 5 ? head.next.next : head;

C. while (head.value !== 5) head = head.next;

D. head.next = null;

Solution

1. Step 1: Check if head node has value 5

   If the first node's value is 5, we remove it by moving head to the next node.

2. Step 2: Verify code correctness

   if (head.value === 5) head = head.next; correctly updates head to head.next if head.value is 5, effectively deleting the first node.

3. Final Answer:

   if (head.value === 5) head = head.next; -> Option A

4. Quick Check:

   Delete head node by reassigning head [OK]

Hint: Check head value first, then update head pointer [OK]

Common Mistakes:

• Using incorrect conditional expressions
• Assigning head.next incorrectly
• Not handling head node deletion
• Overwriting head without checks

3. Given the linked list: 1 -> 3 -> 5 -> 7 -> null, what is the list after deleting the node with value 5 using the following TypeScript code?

let current = head;
while (current.next !== null) {
  if (current.next.value === 5) {
    current.next = current.next.next;
    break;
  }
  current = current.next;
}

medium

A. 1 -> 3 -> 5 -> 7 -> null

B. 1 -> 3 -> 7 -> null

C. 3 -> 5 -> 7 -> null

D. 1 -> 7 -> null

Solution

1. Step 1: Traverse list to find node before value 5

   Loop checks nodes until current.next.value is 5, which is true when current is node with value 3.

2. Step 2: Delete node with value 5 by skipping it

   Set current.next to current.next.next, linking node 3 directly to node 7, removing node 5.

3. Final Answer:

   1 -> 3 -> 7 -> null -> Option B

4. Quick Check:

   Skip node with value 5 = 1->3->7 [OK]

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

Common Mistakes:

• Not breaking loop after deletion
• Deleting wrong node
• Not updating pointers correctly
• Confusing current and current.next

4. Consider this buggy TypeScript code to delete a node by value from a singly linked list:

function deleteNode(head: Node | null, value: number): Node | null {
  let current = head;
  while (current !== null) {
    if (current.next?.value === value) {
      current.next = current.next.next;
    }
    current = current.next!;
  }
  return head;
}

What is the main problem with this code?

medium

A. It may cause a runtime error when current.next is null

B. It deletes all nodes with the value instead of the first

C. It does not handle deletion if head node has the value

D. It reverses the linked list accidentally

Solution

1. Step 1: Analyze the loop termination

   The while (current !== null) continues to the last node where current.next is null. The if uses ?. safely, but then executes current = current.next!;, and ! non-null assertion on null causes runtime error.

2. Step 2: Confirm the bug triggers always

   For any non-empty list, it crashes at the last node regardless of value, preventing correct execution.

3. Final Answer:

   It may cause a runtime error when current.next is null -> Option A

4. Quick Check:

   current.next! on null = runtime error [OK]

Hint: Beware of non-null assertion ! on potentially null next [OK]

Common Mistakes:

• Using non-null assertion (!) on potentially null next
• Assuming current.next always exists
• Not breaking after deletion
• Confusing current and current.next updates

5. You have a singly linked list: 2 -> 4 -> 6 -> 4 -> 8 -> null. You want to delete the first node with value 4. After deletion, you want to insert a new node with value 10 right after the deleted node's position. Which sequence of operations correctly achieves this?

hard

A. Delete first 4, then insert 10 after node 6

B. Insert 10 at head, then delete first 4

C. Delete all 4s, then insert 10 at end

D. Delete first 4, then insert 10 after node 2

Solution

1. Step 1: Delete first node with value 4

   The first 4 is the second node, so remove it by linking node 2 to node 6.

2. Step 2: Insert new node with value 10 after node 2

   Create new node 10 and link it after node 2, then link new node to node 6.

3. Final Answer:

   Delete first 4, then insert 10 after node 2 -> Option D

4. Quick Check:

   Delete 4, insert 10 after previous node [OK]

Hint: Delete node, then insert new node at same position [OK]

Common Mistakes:

• Inserting new node at wrong position
• Deleting all nodes with value 4
• Not updating links correctly
• Inserting before deletion