Get Length of Linked List in DSA C# - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code?

Consider a singly linked list with nodes containing values 10, 20, 30, 40. What will be the output of the GetLength method?

DSA C#

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

public class LinkedList {
    public Node Head;
    public int GetLength() {
        int count = 0;
        Node current = Head;
        while (current != null) {
            count++;
            current = current.Next;
        }
        return count;
    }
}

var list = new LinkedList();
list.Head = new Node(10);
list.Head.Next = new Node(20);
list.Head.Next.Next = new Node(30);
list.Head.Next.Next.Next = new Node(40);

Console.WriteLine(list.GetLength());

A 0

B 4

C 5

D 3

💡 Hint

Count each node starting from the head until you reach the end (null).

The GetLength method counts nodes by traversing from the head until it reaches null. Since there are 4 nodes, the output is 4.

❓ Predict Output

intermediate

What is the output of this code with an empty list?

What will the GetLength method return if the linked list is empty (Head is null)?

DSA C#

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

public class LinkedList {
    public Node Head;
    public int GetLength() {
        int count = 0;
        Node current = Head;
        while (current != null) {
            count++;
            current = current.Next;
        }
        return count;
    }
}

var list = new LinkedList();
Console.WriteLine(list.GetLength());

A Throws NullReferenceException

B 1

C null

D 0

💡 Hint

If the head is null, the loop does not run.

Since Head is null, the while loop never executes and count remains 0, so the method returns 0.

🔧 Debug

advanced

What error does this code raise?

Identify the error when trying to get the length of a linked list with this GetLength method:

DSA C#

public int GetLength() {
    int count = 0;
    Node current = Head;
    while (current.Next != null) {
        count++;
        current = current.Next;
    }
    return count;
}

A Returns correct length

B Throws NullReferenceException

C Returns length minus one

D Infinite loop

💡 Hint

Check the loop condition carefully and what nodes it counts.

The loop stops when current.Next is null, so it does not count the last node, returning length minus one.

❓ Predict Output

advanced

What is the output of this recursive length method?

What will this recursive method return for a linked list with nodes 5 -> 15 -> 25 -> null?

DSA C#

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

public class LinkedList {
    public Node Head;
    public int GetLengthRecursive(Node node) {
        if (node == null) return 0;
        return 1 + GetLengthRecursive(node.Next);
    }
}

var list = new LinkedList();
list.Head = new Node(5);
list.Head.Next = new Node(15);
list.Head.Next.Next = new Node(25);

Console.WriteLine(list.GetLengthRecursive(list.Head));

A 3

B 2

C Throws StackOverflowException

D 0

💡 Hint

Each call counts one node until it reaches null.

The method counts nodes recursively. There are 3 nodes, so it returns 3.

🧠 Conceptual

expert

How many nodes are counted by this method?

Given this method to get length, how many nodes will it count for a linked list with 4 nodes?

DSA C#

public int GetLength(Node node) {
    int count = 0;
    while (node.Next != null) {
        count++;
        node = node.Next;
    }
    return count;
}

A 3

B 4

C 0

D Throws NullReferenceException

💡 Hint

Think about the loop condition and which nodes are counted.

The loop counts nodes while node.Next is not null, so it stops before the last node, counting 3 nodes.

Practice

1. What does the length of a linked list represent?

easy

A. The sum of all node values

B. The value of the first node

C. The memory size of the linked list

D. The number of nodes in the linked list

Solution

1. Step 1: Understand linked list structure

   A linked list is made of nodes connected one after another.

2. Step 2: Define length meaning

   The length is how many nodes are present in the list.

3. Final Answer:

   The number of nodes in the linked list -> Option D

4. Quick Check:

   Length = count of nodes [OK]

Hint: Count nodes to get length quickly [OK]

Common Mistakes:

• Confusing length with node values
• Thinking length is memory size
• Assuming length is sum of values

2. Which of the following C# code snippets correctly initializes a variable to count the length of a linked list?

easy

A. int length = 0;

B. int length = null;

C. string length = "0";

D. bool length = false;

Solution

1. Step 1: Identify correct data type for counting

   Length is a number, so it should be an integer type.

2. Step 2: Check initialization value

   Start counting from zero before traversing nodes.

3. Final Answer:

   int length = 0; -> Option A

4. Quick Check:

   Use int and start at 0 [OK]

Hint: Use int zero to start counting length [OK]

Common Mistakes:

• Using null for int variable
• Using string instead of int
• Using bool for counting

3. What will be the output of the following C# code?

public class Node {
  public int data;
  public Node next;
  public Node(int d) { data = d; next = null; }
}

public class LinkedList {
  public Node head;
  public int GetLength() {
    int count = 0;
    Node current = head;
    while (current != null) {
      count++;
      current = current.next;
    }
    return count;
  }
}

LinkedList list = new LinkedList();
list.head = new Node(5);
list.head.next = new Node(10);
list.head.next.next = new Node(15);
Console.WriteLine(list.GetLength());

medium

A. 0

B. 2

C. 3

D. Error

Solution

1. Step 1: Count nodes in the linked list

   Nodes are 5 -> 10 -> 15, total 3 nodes.

2. Step 2: Trace GetLength method

   Loop increments count for each node until null is reached.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   3 nodes counted = 3 [OK]

Hint: Count each node until null to get length [OK]

Common Mistakes:

• Counting only head node
• Returning zero without counting
• Confusing next pointer with data

4. Identify the error in this C# method to get linked list length:

public int GetLength() {
  int count = 0;
  Node current = head;
  while (current.next != null) {
    count++;
    current = current.next;
  }
  return count;
}

medium

A. It misses counting the last node

B. It causes infinite loop

C. It returns count plus one extra

D. It throws null reference exception

Solution

1. Step 1: Analyze loop condition

   Loop runs while current.next is not null, so last node is skipped.

2. Step 2: Understand counting effect

   Count increments only for nodes before last, missing last node.

3. Final Answer:

   It misses counting the last node -> Option A

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Use current != null to include last node [OK]

Common Mistakes:

• Using current.next != null instead of current != null
• Not incrementing count for last node
• Assuming loop covers all nodes

5. Given a linked list where each node contains an integer, how would you modify the length calculation to count only nodes with even values?

public int GetEvenLength() {
  int count = 0;
  Node current = head;
  while (current != null) {
    // Your code here
    current = current.next;
  }
  return count;
}

hard

A. Add count++ unconditionally inside the loop

B. Add if (current.data % 2 == 0) count++; inside the loop

C. Add if (current.data % 2 != 0) count++; inside the loop

D. Return head.data instead of count

Solution

1. Step 1: Check node value for evenness

   Use modulo operator to test if data is even (data % 2 == 0).

2. Step 2: Increment count only if node is even

   Inside loop, increment count only when condition is true.

3. Final Answer:

   Add if (current.data % 2 == 0) count++; inside the loop -> Option B

4. Quick Check:

   Count only even nodes [OK]

Hint: Use modulo to filter even nodes before counting [OK]

Common Mistakes:

• Counting all nodes without condition
• Counting odd nodes instead of even
• Returning node data instead of count