Insert at End of Doubly Linked List in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given value.

DSA Typescript

const newNode = new Node([1]);

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

Anode

Bvalue

Cdata

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using an undefined variable name instead of the value parameter.

The new node should be created with the value passed as value.

2fill in blank

medium

Complete the code to check if the list is empty (head is null).

DSA Typescript

if (this.head [1] null) {

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A===

B=

C!==

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment '=' instead of comparison '==='.

Using '!==', which checks for not equal.

We check if this.head is exactly equal to null to know if the list is empty.

3fill in blank

hard

Fix the error in the loop condition to find the last node.

DSA Typescript

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

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Atail

Bprev

Chead

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using prev instead of next in the loop condition.

To traverse to the end, we move using the next pointer until it is null.

4fill in blank

hard

Fill both blanks to correctly link the new node at the end.

DSA Typescript

current.[1] = newNode;
newNode.[2] = current;

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

Anext

Bprev

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping next and prev assignments.

Using head or tail properties incorrectly.

The current last node's next points to the new node, and the new node's prev points back to current.

5fill in blank

hard

Fill all three blanks to update the list when inserting the first node.

DSA Typescript

this.head = [1];
this.tail = [2];
newNode.[3] = null;

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

AnewNode

Cprev

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Setting prev to null instead of next.

Not updating both head and tail.

When the list is empty, both head and tail point to the new node, and its next is null.

Practice

1. What is the main purpose of inserting a node at the end of a doubly linked list?

easy

A. To add a new element after the last node

B. To remove the first node

C. To reverse the list

D. To find the middle node

Solution

1. Step 1: Understand the structure of a doubly linked list

   A doubly linked list has nodes connected forward and backward, allowing traversal in both directions.

2. Step 2: Purpose of insertion at the end

   Inserting at the end means adding a new node after the current last node, updating pointers accordingly.

3. Final Answer:

   To add a new element after the last node -> Option A

4. Quick Check:

   Insert at end = add after last node [OK]

Hint: Insert at end means add after last node [OK]

Common Mistakes:

• Confusing insertion at end with deletion
• Thinking insertion reverses the list
• Assuming insertion happens at the start

2. Which of the following TypeScript code snippets correctly initializes a new node for a doubly linked list?

easy

A. const newNode = { data: 5, next: undefined };

B. const newNode = { data: 5, next: null, prev: null };

C. const newNode = { value: 5, nextNode: null };

D. const newNode = { data: 5 };

Solution

1. Step 1: Identify required properties for a doubly linked list node

   A node must have data, next pointer, and prev pointer to link both directions.

2. Step 2: Check each option for correct properties

   const newNode = { data: 5, next: null, prev: null }; has data, next, and prev all properly set. Others miss prev or use wrong property names.

3. Final Answer:

   const newNode = { data: 5, next: null, prev: null }; -> Option B

4. Quick Check:

   Node needs data, next, prev [OK]

Hint: Node needs data, next, and prev properties [OK]

Common Mistakes:

• Omitting prev pointer
• Using wrong property names like value or nextNode
• Setting next or prev as undefined instead of null

3. Given the following TypeScript code for inserting at the end of a doubly linked list, what will be the printed list after insertion?

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

class DoublyLinkedList {
  head: Node | null = null;

  insertAtEnd(data: number) {
    const newNode = new Node(data);
    if (!this.head) {
      this.head = newNode;
      return;
    }
    let temp = this.head;
    while (temp.next) {
      temp = temp.next;
    }
    temp.next = newNode;
    newNode.prev = temp;
  }

  printList() {
    let temp = this.head;
    let result = '';
    while (temp) {
      result += temp.data + ' -> ';
      temp = temp.next;
    }
    result += 'null';
    console.log(result);
  }
}

const dll = new DoublyLinkedList();
dll.insertAtEnd(10);
dll.insertAtEnd(20);
dll.insertAtEnd(30);
dll.printList();

medium

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

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

C. 10 -> 20 -> null

D. null

Solution

1. Step 1: Trace insertAtEnd calls

   First insert adds 10 as head. Second adds 20 after 10. Third adds 30 after 20.

2. Step 2: Trace printList output

   Print starts at head (10), then 20, then 30, then null.

3. Final Answer:

   10 -> 20 -> 30 -> null -> Option A

4. Quick Check:

   Inserted nodes in order = 10 -> 20 -> 30 [OK]

Hint: Insertion at end appends nodes in order [OK]

Common Mistakes:

• Confusing order and printing reversed list
• Missing last inserted node
• Printing null instead of list

4. Identify the error in the following TypeScript method for inserting at the end of a doubly linked list:

insertAtEnd(data: number) {
  const newNode = new Node(data);
  if (!this.head) {
    this.head = newNode;
  }
  let temp = this.head;
  while (temp.next) {
    temp = temp.next;
  }
  temp.next = newNode;
  newNode.prev = temp;
}

medium

A. newNode should be created outside the method

B. Incorrect assignment of newNode.prev

C. Loop condition should be temp !== null

D. Missing return after setting head when list is empty

Solution

1. Step 1: Analyze empty list case

   If head is null, method sets head to newNode but continues to loop and assign next, causing error.

2. Step 2: Fix by adding return after setting head

   Adding return after setting head prevents further code execution and avoids null pointer errors.

3. Final Answer:

   Missing return after setting head when list is empty -> Option D

4. Quick Check:

   Return after head set avoids errors [OK]

Hint: Return immediately after setting head if list empty [OK]

Common Mistakes:

• Not returning after setting head
• Misunderstanding loop condition
• Incorrect pointer assignments

5. You want to insert a new node with data 40 at the end of a doubly linked list that currently has nodes 10 <-> 20 <-> 30. After insertion, what will be the correct state of the list including the prev and next pointers of the new node?

hard

A. 10 <-> 20 <-> 30, with 40.prev and 40.next both null (not linked)

B. 40 <-> 10 <-> 20 <-> 30, where 40.next points to 10 and 40.prev is null

C. 10 <-> 20 <-> 30 <-> 40, where 40.prev points to 30 and 40.next is null

D. 10 <-> 20 <-> 30 <-> 40, where 40.prev and 40.next both point to null

Solution

1. Step 1: Understand insertion at end

   The new node 40 should be linked after 30, so 30.next = 40 and 40.prev = 30.

2. Step 2: Confirm pointers of new node

   Since 40 is last, 40.next must be null to mark list end.

3. Final Answer:

   10 <-> 20 <-> 30 <-> 40, where 40.prev points to 30 and 40.next is null -> Option C

4. Quick Check:

   New tail prev = old tail, next = null [OK]

Hint: New tail node prev = old tail, next = null [OK]

Common Mistakes:

• Setting new node's next pointer incorrectly
• Not linking new node's prev pointer
• Inserting new node at start instead of end