Node Structure and Pointer Design in DSA C# - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a node in data structures?

A node is a basic unit that stores data and references (or pointers) to other nodes, helping to build structures like linked lists and trees.

beginner

What does a pointer in a node do?

A pointer holds the address or reference to another node, allowing nodes to connect and form chains or trees.

beginner

In a singly linked list node, how many pointers are there and what do they point to?

There is one pointer that points to the next node in the list or null if it is the last node.

intermediate

Why do nodes in a doubly linked list have two pointers?

Because one pointer points to the next node and the other points to the previous node, allowing movement in both directions.

beginner

What is the role of a null pointer in node structures?

A null pointer indicates the end of a structure or that there is no node connected in that direction.

How many pointers does a node in a singly linked list have?

A Zero

B Two

C One

D Three

A singly linked list node has one pointer to the next node.

What does a pointer in a node typically store?

A Address of another node

B Data value

C Size of the node

D Type of data

Pointers store the address or reference to another node.

In a doubly linked list, what does the second pointer in a node point to?

A Next node

B Previous node

C Root node

D Null always

The second pointer points to the previous node.

What does a null pointer signify in a linked list?

A Start of the list

B A node with no data

C Middle of the list

D End of the list

Null pointer marks the end of the list.

Which of these is NOT part of a typical node structure?

A Index number

B Data field

C Pointer(s)

D Reference to another node

Nodes usually do not store an index number.

Explain the structure of a node in a singly linked list and how pointers are used.

Think about how nodes connect one after another in one direction.

Describe the difference between pointers in singly and doubly linked list nodes.

Consider how you can move forward and backward in the list.

Practice

1. What is the primary purpose of the next pointer in a singly linked list node?

easy

A. To store the data value of the node

B. To point to the previous node in the list

C. To point to the next node in the list

D. To indicate the end of the list

Solution

1. Step 1: Understand the role of pointers in linked lists

   In a singly linked list, each node contains data and a pointer to the next node to maintain the sequence.

2. Step 2: Identify the function of the next pointer

   The next pointer specifically points to the next node, allowing traversal through the list.

3. Final Answer:

   To point to the next node in the list -> Option C

4. Quick Check:

   next pointer = points to next node [OK]

Hint: Remember: next always moves forward in the list [OK]

Common Mistakes:

• Confusing next with previous pointer
• Thinking next stores data
• Assuming next marks list end

2. Which of the following is the correct way to declare a node class with a pointer to the next node in C#?

easy

A. public class Node { int data; Node next; void Node() {} }

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

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

D. public struct Node { int data; Node next; }

Solution

1. Step 1: Check for correct access modifiers and syntax

   public class Node { public int data; public Node next; } uses public for both data and next pointer, which is standard for node class fields.

2. Step 2: Verify class declaration and member types

   public class Node { public int data; public Node next; } correctly declares a class with an integer data and a pointer to the next node of the same type.

3. Final Answer:

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

4. Quick Check:

   Correct class with public members = public class Node { public int data; public Node next; } [OK]

Hint: Use public class with public fields for simple node design [OK]

Common Mistakes:

• Missing public keyword causing access issues
• Using struct instead of class for linked nodes
• Incorrect constructor syntax

3. Consider the following C# code for a singly linked list node and a small list creation:

public 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);

Console.WriteLine(head.next.next.data);

What will be the output?

medium

A. 3

B. 2

C. NullReferenceException

D. 1

Solution

1. Step 1: Trace node creation and linking

   Head node has data 1, its next points to node with data 2, which in turn points to node with data 3.

2. Step 2: Access head.next.next.data

   This accesses the third node's data, which is 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Third node data = 3 [OK]

Hint: Follow next pointers step-by-step to find data [OK]

Common Mistakes:

• Confusing node positions and accessing wrong data
• Assuming next.next is null
• Expecting runtime error incorrectly

4. Given the following node class and code snippet, identify the error:

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

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

What is the problem here?

medium

A. Data type mismatch in node declaration

B. Node class is missing a constructor

C. No error, code runs fine

D. head.next is null, so accessing head.next.next causes an error

Solution

1. Step 1: Analyze the initial node creation

   Head node is created with data 10, and its next pointer is null by default.

2. Step 2: Check the assignment head.next.next = new Node(20);

   Since head.next is null, trying to access head.next.next causes a NullReferenceException.

3. Final Answer:

   head.next is null, so accessing head.next.next causes an error -> Option D

4. Quick Check:

   Null pointer access causes error [OK]

Hint: Always initialize intermediate nodes before accessing their pointers [OK]

Common Mistakes:

• Assuming next is auto-initialized
• Ignoring null pointer exceptions
• Thinking constructor is missing

5. You want to design a doubly linked list node in C# that can point both to the previous and next nodes. Which of the following class definitions correctly implements this?

hard

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

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

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

D. public struct Node { public int data; public Node prev; public Node next; }

Solution

1. Step 1: Identify the need for both prev and next pointers

   A doubly linked list node must have pointers to both previous and next nodes to allow two-way traversal.

2. Step 2: Check class definition correctness

   public class Node { public int data; public Node prev; public Node next; public Node(int d) { data = d; prev = null; next = null; } } correctly declares public prev and next pointers and initializes them to null in the constructor.

3. Final Answer:

   public class Node { public int data; public Node prev; public Node next; public Node(int d) { data = d; prev = null; next = null; } } -> Option A

4. Quick Check:

   Doubly linked node has both prev and next pointers [OK]

Hint: Doubly linked nodes need both prev and next pointers [OK]

Common Mistakes:

• Omitting the prev pointer
• Using struct instead of class for nodes
• Not initializing pointers in constructor