Insert at Beginning Head Insert in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node and insert it at the beginning of the linked list.

DSA Typescript

const newNode = { value: val, next: [1] };
this.head = newNode;

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

Athis.tail

Bthis.head

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null breaks the chain.

Using tail instead of head causes incorrect linking.

The new node's next should point to the current head to insert it at the beginning.

2fill in blank

medium

Complete the code to update the tail if the list was empty before insertion.

DSA Typescript

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

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

AnewNode

BnewNode.next

Cthis.head

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting tail to null loses the tail reference.

Using newNode.next sets tail to null incorrectly.

If the list was empty, tail should point to the new node after insertion.

3fill in blank

hard

Fix the error in the insertAtBeginning method to correctly update the head pointer.

DSA Typescript

insertAtBeginning(val: number): void {
  const newNode = { value: val, next: this.head };
  this.head = [1];
}

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

Athis.tail

Bval

CnewNode

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to val instead of newNode.

Assigning head to null breaks the list.

The head must be updated to point to the new node after insertion.

4fill in blank

hard

Fill both blanks to complete the method that inserts a new node at the beginning and updates tail if needed.

DSA Typescript

insertAtBeginning(val: number): void {
  const newNode = { value: val, next: [1] };
  this.head = [2];
  if (this.tail === null) {
    this.tail = newNode;
  }
}

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

Athis.head

BnewNode

Cnull

Dthis.tail

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of assignments.

Not updating tail when list is empty.

The new node's next points to current head, then head updates to newNode.

5fill in blank

hard

Fill all three blanks to complete the insertAtBeginning method with proper node creation, head update, and tail check.

DSA Typescript

insertAtBeginning(val: number): void {
  const newNode = { value: val, next: [1] };
  this.head = [2];
  if (this.tail === [3]) {
    this.tail = newNode;
  }
}

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

Athis.head

BnewNode

Cnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using this.tail instead of null in the condition.

Not linking newNode correctly.

newNode.next points to current head, head updates to newNode, tail updates if it was null.

Practice

1. What does the "Insert at Beginning" operation do in a singly linked list?

easy

A. Adds a new node at the start of the list

B. Adds a new node at the end of the list

C. Deletes the first node of the list

D. Deletes the last node of the list

Solution

1. Step 1: Understand the operation

   Inserting at the beginning means adding a new node before the current first node.

2. Step 2: Effect on the list

   The new node becomes the head, pushing the old head to second position.

3. Final Answer:

   Adds a new node at the start of the list -> Option A

4. Quick Check:

   Insert at beginning = Add new head [OK]

Hint: Insert at beginning means new head node [OK]

Common Mistakes:

• Confusing insert at beginning with insert at end
• Thinking it deletes nodes
• Assuming it changes the tail node

2. Which of the following is the correct TypeScript syntax to insert a new node at the beginning of a singly linked list?

easy

A. newNode = head; head.next = newNode;

B. head = newNode.next; newNode = head;

C. head.next = newNode; newNode = head;

D. newNode.next = head; head = newNode;

Solution

1. Step 1: Link new node to current head

   Set newNode.next to point to current head node.

2. Step 2: Update head to new node

   Assign head to newNode so it becomes the first node.

3. Final Answer:

   newNode.next = head; head = newNode; -> Option D

4. Quick Check:

   Link new node to head, then update head [OK]

Hint: Set newNode.next to head, then head = newNode [OK]

Common Mistakes:

• Assigning head before linking newNode.next
• Swapping assignments order
• Using head.next instead of newNode.next

3. What will be the linked list after executing the following TypeScript code?

class Node {
  value: number;
  next: Node | null = null;
  constructor(value: number) { this.value = value; }
}

let head: Node | null = new Node(10);
let newNode = new Node(5);
newNode.next = head;
head = newNode;

medium

A. 10 -> null

B. 10 -> 5 -> null

C. 5 -> 10 -> null

D. 5 -> null

Solution

1. Step 1: Initial list setup

   head points to node with value 10, next is null.

2. Step 2: Insert newNode at beginning

   newNode (5) points to head (10), then head updated to newNode.

3. Final Answer:

   5 -> 10 -> null -> Option C

4. Quick Check:

   New node 5 becomes head, points to 10 [OK]

Hint: New node points to old head, then becomes new head [OK]

Common Mistakes:

• Confusing order of nodes after insertion
• Forgetting to update head
• Assuming newNode.next is null

4. Identify the error in this TypeScript code that tries to insert a node at the beginning of a linked list:

class Node {
  value: number;
  next: Node | null = null;
  constructor(value: number) { this.value = value; }
}

let head: Node | null = null;
let newNode = new Node(7);
head.next = newNode;
head = newNode;

medium

A. head is null, so head.next causes an error

B. newNode is not linked to head

C. head should be assigned before newNode.next

D. Missing constructor call for newNode

Solution

1. Step 1: Check initial head value

   head is null, so accessing head.next is invalid and causes runtime error.

2. Step 2: Correct insertion approach

   Assign newNode.next = head (which is null), then head = newNode.

3. Final Answer:

   head is null, so head.next causes an error -> Option A

4. Quick Check:

   Cannot access property on null head [OK]

Hint: Check if head is null before accessing head.next [OK]

Common Mistakes:

• Trying to access next on null head
• Not linking newNode.next to head
• Assigning head after using head.next

5. Given a singly linked list with nodes 20 -> 30 -> 40 -> null, what will be the list after inserting 10 at the beginning using head insert method?

hard

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

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

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

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

Solution

1. Step 1: Understand initial list

   List is 20 -> 30 -> 40 -> null, head points to 20.

2. Step 2: Insert 10 at beginning

   Create new node 10, set newNode.next = head (20), then head = newNode.

3. Final Answer:

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

4. Quick Check:

   New node 10 becomes head, old list follows [OK]

Hint: New node points to old head, becomes new head [OK]

Common Mistakes:

• Appending new node at end instead of beginning
• Mixing node order after insertion
• Not updating head pointer