Enqueue Using Linked List in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node for enqueue operation.

DSA C#

Node newNode = new Node([1]);

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

Ahead

Bnull

Cvalue

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'null' instead of the value for the new node.

Using 'head' or 'tail' which are pointers, not the data.

We create a new node with the given value to enqueue it into the linked list queue.

2fill in blank

medium

Complete the code to check if the queue is empty before enqueue.

DSA C#

if (tail == [1]) { head = newNode; tail = newNode; } else { tail.next = newNode; tail = newNode; }

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

Anull

Bhead

CnewNode

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if tail equals head instead of null.

Assigning tail to newNode before checking.

If tail is null, the queue is empty, so both head and tail point to the new node.

3fill in blank

hard

Fix the error in the enqueue method to link the new node correctly.

DSA C#

tail.[1] = newNode; tail = newNode;

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

Aprev

Bnext

Chead

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists.

Assigning to 'head' or 'value' which are incorrect.

The 'next' pointer of the current tail should point to the new node.

4fill in blank

hard

Fill both blanks to complete the enqueue method for linked list queue.

DSA C#

public void Enqueue(int value) {
    Node newNode = new Node(value);
    if (tail == [1]) {
        head = newNode;
        tail = newNode;
    } else {
        tail.[2] = newNode;
        tail = newNode;
    }
}

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

Anull

Bhead

Cnext

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' instead of null for empty check.

Using 'prev' instead of 'next' for linking.

Check if tail is null to detect empty queue, then link new node using 'next' pointer.

5fill in blank

hard

Fill all three blanks to implement enqueue operation correctly.

DSA C#

public void Enqueue(int [1]) {
    Node newNode = new Node([2]);
    if (tail == [3]) {
        head = newNode;
        tail = newNode;
    } else {
        tail.next = newNode;
        tail = newNode;
    }
}

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

Avalue

Bnull

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for parameter and node value.

Checking if tail equals head instead of null.

Parameter name and node value use 'value'; check if tail is null for empty queue.

Practice

1. What does the Enqueue operation do in a linked list implementation of a queue?

easy

A. Adds an element at the front of the linked list

B. Removes an element from the front of the linked list

C. Deletes the last element of the linked list

D. Adds an element at the end of the linked list

Solution

1. Step 1: Understand enqueue operation

   Enqueue means adding an element to the queue.

2. Step 2: Identify linked list behavior for enqueue

   In a linked list queue, enqueue adds the new node at the end (tail).

3. Final Answer:

   Adds an element at the end of the linked list -> Option D

4. Quick Check:

   Enqueue = Add at tail [OK]

Hint: Enqueue always adds at the tail in linked list queue [OK]

Common Mistakes:

• Confusing enqueue with dequeue operation
• Adding element at the front instead of the end
• Thinking enqueue removes elements

2. Which of the following is the correct syntax to create a new node and enqueue it in a linked list queue in C#?

easy

A. Node newNode = new Node(data); tail.next = newNode; tail = newNode;

B. Node newNode = Node(data); tail.next = newNode; tail = newNode;

C. Node newNode = new Node(); tail = newNode; tail.next = data;

D. Node newNode = new Node(data); head.next = newNode; head = newNode;

Solution

1. Step 1: Create new node with data

   Use 'new Node(data)' to create a node with the given data.

2. Step 2: Link new node at tail and update tail

   Set 'tail.next = newNode' and then update 'tail = newNode' to keep tail at last node.

3. Final Answer:

   Node newNode = new Node(data); tail.next = newNode; tail = newNode; -> Option A

4. Quick Check:

   Correct node creation and tail update [OK]

Hint: Use 'new' keyword and update tail pointer [OK]

Common Mistakes:

• Forgetting 'new' keyword when creating node
• Updating head instead of tail
• Assigning data to next pointer

3. What will be the state of the queue after executing the following C# code?

QueueLinkedList queue = new QueueLinkedList();
queue.Enqueue(10);
queue.Enqueue(20);
queue.Enqueue(30);

Assuming the queue prints elements from head to tail.

medium

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

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

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

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

Solution

1. Step 1: Enqueue 10, 20, 30 in order

   Each enqueue adds element at the tail, so order is 10, then 20, then 30.

2. Step 2: Print queue from head to tail

   Head points to 10, followed by 20, then 30, ending with null.

3. Final Answer:

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

4. Quick Check:

   Enqueue order preserved from head to tail [OK]

Hint: Enqueue adds at tail, print from head to tail [OK]

Common Mistakes:

• Reversing the order of elements
• Confusing head and tail pointers
• Assuming enqueue adds at head

4. Identify the error in the following enqueue method for a linked list queue in C#:

public void Enqueue(int data) {
    Node newNode = new Node(data);
    if (head == null) {
        head = newNode;
    } else {
        tail.next = newNode;
    }
}

medium

A. New node should be created outside the method

B. The tail pointer is not updated after adding new node

C. The head pointer should be updated instead of tail

D. The if condition should check tail instead of head

Solution

1. Step 1: Check tail update after enqueue

   After adding newNode at tail.next, tail must be updated to newNode.

2. Step 2: Identify missing tail update

   Code does not update tail, so tail still points to old last node, causing errors.

3. Final Answer:

   The tail pointer is not updated after adding new node -> Option B

4. Quick Check:

   Always update tail after enqueue [OK]

Hint: Update tail pointer after adding new node [OK]

Common Mistakes:

• Forgetting to update tail pointer
• Updating head instead of tail
• Creating node outside enqueue method

5. Given a linked list queue with elements 5 -> 15 -> 25 -> null, what will be the queue state after enqueueing 35 and then dequeueing one element?

hard

A. 25 -> 35 -> null

B. 5 -> 15 -> 25 -> 35 -> null

C. 15 -> 25 -> 35 -> null

D. 35 -> 5 -> 15 -> 25 -> null

Solution

1. Step 1: Enqueue 35 at tail

   Queue becomes 5 -> 15 -> 25 -> 35 -> null after enqueue.

2. Step 2: Dequeue removes from head

   Removing 5 from head leaves 15 -> 25 -> 35 -> null.

3. Final Answer:

   15 -> 25 -> 35 -> null -> Option C

4. Quick Check:

   Enqueue adds tail, dequeue removes head [OK]

Hint: Enqueue tail, dequeue head to update queue [OK]

Common Mistakes:

• Removing from tail instead of head
• Not updating head after dequeue
• Adding new element at head instead of tail