Get Length of Linked List in DSA C# - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a linked list?

A linked list is a chain of nodes where each node holds data and a reference (link) to the next node. It is like a treasure hunt where each clue leads to the next one.

beginner

How do you find the length of a linked list?

Start at the first node and move through each node one by one, counting each node until you reach the end (null). The count is the length.

beginner

What does the 'null' reference mean in a linked list?

It means the end of the list. When a node's next link is null, there are no more nodes after it.

intermediate

Why can't we use an index to find the length of a linked list like in arrays?

Because linked lists don't store elements in continuous memory, so we can't jump to a position directly. We must visit each node one by one.

intermediate

What is the time complexity of finding the length of a linked list?

It is O(n), where n is the number of nodes, because you must visit each node once to count them.

What is the first step to find the length of a linked list?

A Jump to the last node directly

B Reverse the linked list

C Use an index to access nodes

D Start counting from the head node

You start counting from the head node and move through each node until the end.

What does a 'null' next pointer in a node indicate?

A The node points to itself

B The node is the last in the list

C The list is empty

D The node has multiple next nodes

A null next pointer means this node is the last one in the linked list.

Why can't we use direct indexing to find length in a linked list?

A Because nodes are not stored in continuous memory

B Because linked lists are sorted

C Because linked lists have no head

D Because linked lists are immutable

Nodes in a linked list are scattered in memory, so we must traverse them one by one.

What is the time complexity to find the length of a linked list with n nodes?

A O(n)

B O(log n)

C O(n^2)

D O(1)

You must visit each node once, so the time complexity is O(n).

If a linked list is empty, what is its length?

A Undefined

B 1

C 0

D Null

An empty linked list has zero nodes, so its length is 0.

Explain step-by-step how to find the length of a linked list.

Think of walking through a chain counting each link.

Why is traversing each node necessary to find the length of a linked list?

Compare with arrays and their indexing.

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