Traversal and Printing a Linked List in DSA C# - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of traversing a linked list?

To visit each node in the linked list one by one, usually to read or process the data stored in each node.

beginner

In a singly linked list, how do you move from one node to the next?

By following the 'next' pointer/reference in the current node to reach the next node.

beginner

What condition tells you that you have reached the end of a linked list during traversal?

When the current node's 'next' pointer is null, it means there are no more nodes to visit.

beginner

Why is it important to start traversal from the head node of a linked list?

Because the head node is the entry point to the list; without it, you cannot access the rest of the nodes.

beginner

What is the output format when printing a linked list like 1 -> 2 -> 3 -> null?

It shows the sequence of node values connected by arrows, ending with 'null' to indicate the list's end.

What does the 'next' pointer in a linked list node represent?

A The address of the next node in the list

B The data stored in the node

C The previous node in the list

D The size of the list

The 'next' pointer holds the reference to the next node, allowing traversal through the list.

When traversing a linked list, which node do you start from?

A The tail node

B The middle node

C The head node

D Any random node

Traversal always starts from the head node because it is the first node in the list.

How do you know you have reached the end of a singly linked list?

A When the current node's next pointer is null

B When the current node's data is null

C When the list size is zero

D When the current node points to the head

The end of the list is indicated by a null 'next' pointer in the last node.

What will be printed for an empty linked list?

A 0

B Error

C Empty

D null

An empty linked list is represented by 'null' since there are no nodes to print.

Which of these is the correct way to print a linked list with nodes 1, 2, 3?

A [1, 2, 3]

B 1 -> 2 -> 3 -> null

C 1, 2, 3

D 1 2 3

The arrow notation shows the links between nodes and ends with 'null' to indicate the list end.

Explain step-by-step how to traverse and print all elements of a singly linked list.

Think about how you move from one node to the next and when to stop.

Describe what happens if you try to traverse a linked list starting from a node other than the head.

Consider the linked list as a chain starting at the head.

Practice

1. What does traversing a linked list mean in simple terms?

easy

A. Reversing the order of nodes

B. Visiting each node one by one from start to end

C. Deleting the first node

D. Adding a new node at the end

Solution

1. Step 1: Understand traversal

   Traversal means going through each node in the linked list starting from the first node.

2. Step 2: Identify what happens during traversal

   We visit each node one by one until we reach the end (null).

3. Final Answer:

   Visiting each node one by one from start to end -> Option B

4. Quick Check:

   Traversal = Visit nodes sequentially [OK]

Hint: Traversal means visiting nodes one after another [OK]

Common Mistakes:

• Confusing traversal with adding or deleting nodes
• Thinking traversal changes the list order
• Assuming traversal skips nodes

2. Which of the following is the correct C# syntax to start traversing a singly linked list named head?

easy

A. Node current => head;

B. Node current == head;

C. Node current = head;

D. Node current <- head;

Solution

1. Step 1: Check variable assignment syntax in C#

   In C#, to assign a value, use a single equals sign (=), not double (==) or arrows.

2. Step 2: Identify correct assignment for traversal start

   We assign the head node to a variable to start traversal: Node current = head;

3. Final Answer:

   Node current = head; -> Option C

4. Quick Check:

   Assignment uses =, not == or arrows [OK]

Hint: Use single = for assignment in C# [OK]

Common Mistakes:

• Using == instead of = for assignment
• Using arrow symbols which are invalid
• Confusing assignment with comparison

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

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

Node head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);

Node current = head;
while (current != null) {
  Console.Write(current.data + " -> ");
  current = current.next;
}
Console.WriteLine("null");

medium

A. 1 -> 2 -> 3 -> null

B. null -> 1 -> 2 -> 3

C. 3 -> 2 -> 1 -> null

D. 1 2 3 null

Solution

1. Step 1: Understand the linked list structure

   The list has nodes with data 1, 2, and 3 linked in order.

2. Step 2: Trace the while loop output

   The loop prints each node's data followed by ' -> ', then moves to next node until null.

3. Final Answer:

   1 -> 2 -> 3 -> null -> Option A

4. Quick Check:

   Print nodes in order with arrows and end with null [OK]

Hint: Print nodes in order, end with null [OK]

Common Mistakes:

• Printing nodes in reverse order
• Missing arrows or null in output
• Printing null at start instead of end

4. Identify the error in this linked list traversal code snippet:

Node current = head;
while (current.next != null) {
  Console.Write(current.data + " -> ");
  current = current.next;
}
Console.WriteLine("null");

medium

A. It prints nodes in reverse order

B. It causes a null reference exception

C. It never enters the loop

D. It skips printing the last node's data

Solution

1. Step 1: Analyze the loop condition

   The loop runs while current.next is not null, so it stops before the last node.

2. Step 2: Check what gets printed

   Since the last node's data is printed only inside the loop, it is skipped.

3. Final Answer:

   It skips printing the last node's data -> Option D

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
• Assuming last node prints automatically
• Confusing loop condition with node data access

5. Given a singly linked list, how would you modify the traversal code to print the list in reverse order without changing the list structure?

hard

A. Use recursion to print nodes after recursive call returns

B. Traverse normally and print nodes immediately

C. Reverse the list first then print

D. Use a for loop with index to print backwards

Solution

1. Step 1: Understand the problem constraints

   We cannot change the list structure, so reversing the list is not allowed.

2. Step 2: Use recursion to print in reverse

   Recursion visits nodes forward, then prints after returning, effectively printing backwards.

3. Final Answer:

   Use recursion to print nodes after recursive call returns -> Option A

4. Quick Check:

   Recursion prints in reverse without modifying list [OK]

Hint: Recursion prints reverse by printing after calls return [OK]

Common Mistakes:

• Trying to use index-based loops on linked list
• Reversing list which changes structure
• Printing nodes immediately during traversal