Pop Using Linked List Node in DSA C# - Build from Scratch

Pop Using Linked List Node

📖 Scenario: Imagine you have a stack of books represented as a linked list. You want to remove the top book from the stack, which means popping the first node from the linked list.

🎯 Goal: You will create a linked list with three nodes, then write code to pop (remove) the first node from the list, and finally print the remaining linked list.

📋 What You'll Learn

Create a linked list with nodes containing values 10, 20, and 30 in that order

Create a method to pop the first node from the linked list

Print the linked list after popping the first node

💡 Why This Matters

🌍 Real World

Linked lists are used in many applications like undo functionality, navigation history, and managing playlists where items are added or removed dynamically.

💼 Career

Understanding linked list operations like pop is essential for software developers working with data structures, memory management, and algorithm optimization.

1

Create the Linked List Nodes

Create a class called Node with an int field called Value and a Node field called Next. Then create three nodes with values 10, 20, and 30 linked together in that order. Store the first node in a variable called head.

DSA C#

// Define the Node class and create the linked list nodes
// Your code here

Hint

Define the Node class with Value and Next. Then link nodes by setting Next of each node.

2

Create a Pop Method

Create a method called Pop that takes a Node called head and returns the new head after removing the first node. The method should return null if the list is empty.

DSA C#

public class Node
{
    public int Value;
    public Node Next;

    public Node(int value)
    {
        Value = value;
        Next = null;
    }
}

Node head = new Node(10);
head.Next = new Node(20);
head.Next.Next = new Node(30);

// Create the Pop method below
// Your code here

Hint

The Pop method should check if head is null. If not, return head.Next as the new head.

3

Pop the First Node

Call the Pop method with the variable head and assign the result back to head to remove the first node.

DSA C#

public class Node
{
    public int Value;
    public Node Next;

    public Node(int value)
    {
        Value = value;
        Next = null;
    }
}

Node head = new Node(10);
head.Next = new Node(20);
head.Next.Next = new Node(30);

Node Pop(Node head)
{
    if (head == null)
        return null;
    return head.Next;
}

// Pop the first node and update head
// Your code here

Hint

Assign the result of Pop(head) back to head to remove the first node.

4

Print the Remaining Linked List

Use a while loop with a variable current starting at head to print each node's Value followed by " -> ". After the loop, print "null" to show the end of the list.

DSA C#

public class Node
{
    public int Value;
    public Node Next;

    public Node(int value)
    {
        Value = value;
        Next = null;
    }
}

Node head = new Node(10);
head.Next = new Node(20);
head.Next.Next = new Node(30);

Node Pop(Node head)
{
    if (head == null)
        return null;
    return head.Next;
}

head = Pop(head);

// Print the linked list
// Your code here

Hint

Use a while loop to go through each node starting from head. Print the Value and " -> ". After the loop, print "null".

Practice

1. What does the pop operation do in a linked list when implemented using nodes?

easy

A. Searches for a node with a specific value

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

C. Counts the total number of nodes in the linked list

D. Removes and returns the first node from the linked list

Solution

1. Step 1: Understand the pop operation

   The pop operation removes an element from a data structure. In a linked list, it usually removes the first node (head).

2. Step 2: Identify the effect on the linked list

   Removing the first node means the head pointer moves to the next node, and the removed node is returned.

3. Final Answer:

   Removes and returns the first node from the linked list -> Option D

4. Quick Check:

   Pop = Remove first node [OK]

Hint: Pop removes the first node in a linked list [OK]

Common Mistakes:

• Confusing pop with adding nodes
• Thinking pop removes the last node
• Assuming pop counts nodes

2. Which of the following is the correct syntax to pop a node from the head of a singly linked list in C#?

easy

A. head = null; return head;

B. head = head.next; return head;

C. Node temp = head; head = head.next; return temp;

D. Node temp = head.next; head = temp; return head;

Solution

1. Step 1: Save the current head node

   We store the current head in a temporary variable to return it later.

2. Step 2: Move head to the next node

   Update the head pointer to the next node in the list.

3. Step 3: Return the removed node

   Return the saved node which was the original head.

4. Final Answer:

   Node temp = head; head = head.next; return temp; -> Option C

5. Quick Check:

   Save head, move head next, return saved [OK]

Hint: Save head, move head to next, return saved node [OK]

Common Mistakes:

• Returning the new head instead of removed node
• Not saving the original head before moving
• Setting head to null incorrectly

3. Consider the following C# code for popping a node from a linked list:

Node head = new Node(10);
head.next = new Node(20);
head.next.next = new Node(30);

Node popped = Pop(ref head);
Console.WriteLine(popped.data);

What will be printed?

Assume Pop removes the first node and updates head.

medium

A. 10

B. 20

C. 30

D. NullReferenceException

Solution

1. Step 1: Understand initial linked list

   The list has nodes 10 -> 20 -> 30. Head points to node with data 10.

2. Step 2: Pop removes the first node

   Pop removes node 10 and updates head to node 20.

3. Step 3: Output the popped node's data

   The popped node's data is 10, so Console.WriteLine prints 10.

4. Final Answer:

   10 -> Option A

5. Quick Check:

   First node data popped = 10 [OK]

Hint: Pop returns first node's data before head moves [OK]

Common Mistakes:

• Printing head data after pop instead of popped node
• Confusing node values order
• Assuming pop returns null

4. The following C# method is intended to pop the first node from a linked list:

Node Pop(Node head) {
    Node temp = head;
    head = head.next;
    return temp;
}

What is the main problem with this code?

medium

A. It does not update the original head outside the method

B. It returns the wrong node

C. It causes a null pointer exception always

D. It deletes the entire linked list

Solution

1. Step 1: Analyze parameter passing

   The method receives head by value, so changes to head inside do not affect the caller's head.

2. Step 2: Understand effect on original list

   Since head is not updated outside, the original list's head remains unchanged, so pop does not remove the node effectively.

3. Final Answer:

   It does not update the original head outside the method -> Option A

4. Quick Check:

   Head passed by value, original not updated [OK]

Hint: Use ref to update head outside method [OK]

Common Mistakes:

• Assuming head changes inside method affect caller
• Thinking it returns wrong node
• Believing it causes runtime error

5. You have a singly linked list with nodes: 5 -> 15 -> 25 -> null.
You want to pop two nodes using a method that updates the head by reference.
After popping twice, what is the state of the linked list?

hard

A. 15 -> 25 -> null

B. 25 -> null

C. 5 -> 15 -> 25 -> null

D. null

Solution

1. Step 1: Initial linked list nodes

   The list starts as 5 -> 15 -> 25 -> null, head points to node with 5.

2. Step 2: Pop first node

   Pop removes node 5, head moves to node 15, list becomes 15 -> 25 -> null.

3. Step 3: Pop second node

   Pop removes node 15, head moves to node 25, list becomes 25 -> null.

4. Final Answer:

   25 -> null -> Option B

5. Quick Check:

   Two pops remove first two nodes [OK]

Hint: Each pop removes head, so two pops leave third node [OK]

Common Mistakes:

• Not updating head after pop
• Assuming popped nodes remain in list
• Confusing node order after pops