Why Linked List Exists and What Problem It Solves in DSA C# - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node in a linked list.

DSA C#

Node newNode = new Node([1]);

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

Avalue

Bnext

Chead

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing 'next' instead of the actual value.

Using 'null' as the value when creating a node.

The new node must be created with a value, so we pass value to the constructor.

2fill in blank

medium

Complete the code to add a new node at the beginning of the linked list.

DSA C#

newNode.[1] = head;
head = newNode;

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

Avalue

Bnext

Cprev

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' or 'data' instead of 'next'.

Not updating the head after linking.

We set the next pointer of the new node to the current head to link it properly.

3fill in blank

hard

Fix the error in the code that tries to traverse the linked list.

DSA C#

Node current = head;
while (current != [1]) {
    Console.WriteLine(current.value);
    current = current.next;
}

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

Ahead

BnewNode

Cnull

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Checking if current is head inside the loop.

Using 'next' or 'newNode' as the loop condition.

The loop should continue until current is null, which means the end of the list.

4fill in blank

hard

Fill both blanks to complete the code that inserts a node after a given node.

DSA C#

newNode.[1] = prevNode.[2];
prevNode.next = newNode;

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

Anext

Bvalue

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' or 'prev' instead of 'next'.

Not updating the previous node's next pointer.

The new node's next should point to the previous node's next, then the previous node's next is updated to the new node.

5fill in blank

hard

Fill all three blanks to complete the code that removes the first node from the linked list.

DSA C#

if (head != [1]) {
    Node temp = head;
    head = head.[2];
    temp.[3] = null;
}

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

Anull

Bnext

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking if the list is empty before removal.

Forgetting to disconnect the removed node.

We check if head is not null, then move head to the next node, and finally disconnect the removed node by setting its next to null.

Practice

1. Why do we use a linked list instead of an array in some cases?

easy

A. Because linked lists are faster for accessing elements by index

B. Because linked lists allow easy insertion and deletion without shifting elements

C. Because linked lists store elements in contiguous memory locations

D. Because linked lists use less memory than arrays always

Solution

1. Step 1: Understand array limitations

   Arrays store elements in contiguous memory, so inserting or deleting elements requires shifting others, which is slow.

2. Step 2: Understand linked list advantage

   Linked lists store elements in nodes connected by pointers, so insertion and deletion can be done by changing pointers without shifting.

3. Final Answer:

   Because linked lists allow easy insertion and deletion without shifting elements -> Option B

4. Quick Check:

   Insertion/deletion ease = D [OK]

Hint: Linked lists excel at insert/delete without shifting [OK]

Common Mistakes:

• Thinking linked lists always use less memory
• Believing linked lists store elements contiguously
• Assuming linked lists have fast random access

2. Which of the following is the correct way to declare a node class for a singly linked list in C#?

easy

A. public class Node { int data; int next; }

B. class Node { public int data; public int next; }

C. public class Node { public int data; public Node next; }

D. public class Node { public int data; public Node previous; }

Solution

1. Step 1: Check node data types

   A node should store data and a reference to the next node, so data is int and next is Node type.

2. Step 2: Validate options

   public class Node { public int data; public Node next; } correctly declares data as int and next as Node. public class Node { int data; int next; } uses int for next which is wrong. class Node { public int data; public int next; } misses public for class and next is int. public class Node { public int data; public Node previous; } uses previous which is for doubly linked list, not singly.

3. Final Answer:

   public class Node { public int data; public Node next; } -> Option C

4. Quick Check:

   Node with int data and Node next = B [OK]

Hint: Node next must be Node type, not int [OK]

Common Mistakes:

• Using int type for next pointer
• Missing public access modifier
• Confusing singly and doubly linked list node

3. What will be the output of the following C# code that creates a linked list and prints its elements?

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

class Program {
  static void Main() {
    Node head = new Node(10);
    head.next = new Node(20);
    head.next.next = new Node(30);

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

medium

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

B. 10 -> 20 -> null

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

D. Compilation error

Solution

1. Step 1: Build linked list nodes

   Nodes created with data 10, 20, 30 linked in order: 10 -> 20 -> 30.

2. Step 2: Traverse and print nodes

   Loop prints each node's data followed by ' -> ', ending with 'null'. Output is 10 -> 20 -> 30 -> null.

3. Final Answer:

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

4. Quick Check:

   Traverse linked list prints nodes in order [OK]

Hint: Traverse from head, print data until null [OK]

Common Mistakes:

• Printing nodes in reverse order
• Missing last node in output
• Confusing next pointer usage

4. The following code tries to insert a new node with value 15 after the head node in a linked list. What is the error?

Node head = new Node(10);
head.next = new Node(20);
Node newNode = new Node(15);
newNode.next = head.next;
head.next = newNode.next;

medium

A. head should be null before insertion

B. newNode.next should be null

C. No error, code works fine

D. head.next is assigned incorrectly, losing the new node

Solution

1. Step 1: Analyze pointer assignments

   newNode.next is set to head.next (which is node with 20), correct for insertion.

2. Step 2: Check head.next assignment

   head.next is set to newNode.next, which points to node 20, so newNode is skipped and lost.

3. Final Answer:

   head.next is assigned incorrectly, losing the new node -> Option D

4. Quick Check:

   head.next must point to newNode, not newNode.next [OK]

Hint: head.next should point to newNode, not newNode.next [OK]

Common Mistakes:

• Assigning head.next to newNode.next instead of newNode
• Setting newNode.next to null incorrectly
• Not updating pointers in correct order

5. You want to implement a playlist where songs can be added or removed frequently at any position. Why is a linked list a better choice than an array for this use case?

hard

A. Because linked lists allow dynamic memory allocation and efficient insertions/removals anywhere

B. Because arrays automatically resize and are faster for insertions

C. Because linked lists store elements contiguously for faster access

D. Because arrays use pointers to link elements like linked lists

Solution

1. Step 1: Understand playlist operations

   Playlist requires frequent insertions and deletions at any position, which can be slow in arrays due to shifting.

2. Step 2: Compare data structures

   Linked lists allocate memory dynamically and allow changing pointers to insert or remove nodes efficiently without shifting elements.

3. Final Answer:

   Because linked lists allow dynamic memory allocation and efficient insertions/removals anywhere -> Option A

4. Quick Check:

   Dynamic insert/delete efficiency = A [OK]

Hint: Linked lists handle frequent insert/delete better than arrays [OK]

Common Mistakes:

• Thinking arrays resize automatically without cost
• Believing linked lists store elements contiguously
• Confusing arrays with pointer-based structures