Singly linked list structure in Data Structures Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the basic node structure of a singly linked list

Which of the following best describes the structure of a single node in a singly linked list?

A A node contains data and a reference to the next node only.

B A node contains data and references to both the previous and next nodes.

C A node contains only data without any references to other nodes.

D A node contains data and a reference to the previous node only.

💡 Hint

Think about how nodes connect in one direction only.

In a singly linked list, each node holds data and a reference (or pointer) to the next node. It does not have a reference to the previous node.

📋 Factual

intermediate

Number of references in a singly linked list node

How many references (or pointers) does each node in a singly linked list contain?

A Two references: one to the previous node and one to the next node.

B One reference: to the next node only.

C No references; nodes are independent.

D Three references: to previous, next, and head nodes.

💡 Hint

Remember, singly linked lists connect nodes in one direction.

Each node in a singly linked list has exactly one reference, which points to the next node in the sequence.

🔍 Analysis

advanced

Identifying the end of a singly linked list

In a singly linked list, how can you identify the last node?

A The last node's next reference is null or None.

B The last node's next reference points to the head node.

C The last node has a reference to the previous node only.

D The last node contains no data.

💡 Hint

Think about what indicates the end of the list in a chain of nodes.

The last node in a singly linked list has its next reference set to null (or None), indicating no further nodes.

❓ Comparison

advanced

Difference between singly and doubly linked list nodes

Which statement correctly contrasts nodes in singly linked lists versus doubly linked lists?

A Singly linked list nodes have two references; doubly linked list nodes have one.

B Singly linked list nodes have no references; doubly linked list nodes have one.

C Both singly and doubly linked list nodes have the same number of references.

D Singly linked list nodes have one reference; doubly linked list nodes have two references.

💡 Hint

Consider how nodes connect in both directions in doubly linked lists.

Singly linked list nodes have one reference to the next node, while doubly linked list nodes have two references: one to the next node and one to the previous node.

❓ Reasoning

expert

Effect of missing next reference in a singly linked list node

What happens if a node in a singly linked list has its next reference accidentally set to null (None) before the actual end of the list?

A The list continues normally without any effect.

B The list automatically reconnects to the next node after the null reference.

C The list traversal stops prematurely, losing access to subsequent nodes.

D The node becomes the new head of the list.

💡 Hint

Think about how traversal depends on the next reference.

If a node's next reference is set to null before the list's actual end, traversal stops at that node, and all nodes after it become unreachable.

Practice

1. What does each node in a singly linked list contain?

easy

A. Only data without any pointers

B. Data and pointers to both next and previous nodes

C. Data and a pointer to the next node

D. Only a pointer to the previous node

Solution

1. Step 1: Understand node structure in singly linked list

   Each node stores some data and a pointer to the next node only, not to the previous one.

2. Step 2: Compare options with definition

   Data and a pointer to the next node matches the definition exactly. Data and pointers to both next and previous nodes describes a doubly linked list. Options C and D miss the pointer to the next node.

3. Final Answer:

   Data and a pointer to the next node -> Option C

4. Quick Check:

   Node = data + next pointer [OK]

Hint: Remember: singly linked means one pointer per node [OK]

Common Mistakes:

• Confusing singly linked with doubly linked list
• Thinking nodes have no pointers
• Assuming pointer to previous node exists

2. Which of the following is the correct way to represent the head of a singly linked list in code?

easy

A. head = None

B. head = head.next

C. head = head.prev

D. head = data

Solution

1. Step 1: Understand the head pointer initialization

   The head points to the first node or is None if the list is empty.

2. Step 2: Analyze options

   head = None correctly initializes head as None for an empty list. head = head.next tries to move head to next node, which is invalid if list is empty. head = head.prev uses prev pointer which does not exist in singly linked list. head = data assigns data to head, which is incorrect.

3. Final Answer:

   head = None -> Option A

4. Quick Check:

   Empty list head = None [OK]

Hint: Head starts as None when list is empty [OK]

Common Mistakes:

• Using prev pointer in singly linked list
• Assigning data directly to head
• Moving head before list has nodes

3. Given the following singly linked list nodes:

node1 = Node(data=10, next=node2)
node2 = Node(data=20, next=node3)
node3 = Node(data=30, next=None)
head = node1

What is the data value of head.next.next?

medium

A. 20

B. 30

C. 10

D. None

Solution

1. Step 1: Trace the linked nodes from head

   head points to node1 with data 10. head.next points to node2 with data 20. head.next.next points to node3 with data 30.

2. Step 2: Identify the data at head.next.next

   The data at node3 is 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   head.next.next.data = 30 [OK]

Hint: Follow next pointers step-by-step [OK]

Common Mistakes:

• Confusing node positions
• Assuming next of last node is not None
• Mixing data values with node references

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

new_node = Node(data=5)
new_node.next = head
head = new_node.next

medium

A. new_node.next should be None

B. No error, code is correct

C. Data assignment to new_node is missing

D. head should be assigned to new_node, not new_node.next

Solution

1. Step 1: Understand insertion at head

   To insert new_node at the start, new_node.next should point to current head, then head should be updated to new_node.

2. Step 2: Analyze the code error

   The code sets new_node.next = head correctly, but then sets head = new_node.next, which points to old head, not new_node. This loses the new node as head.

3. Final Answer:

   head should be assigned to new_node, not new_node.next -> Option D

4. Quick Check:

   head = new_node after insertion [OK]

Hint: After linking, head must point to new_node [OK]

Common Mistakes:

• Assigning head to new_node.next instead of new_node
• Forgetting to link new_node.next to old head
• Not updating head pointer after insertion

5. You want to reverse a singly linked list with nodes:

head -> node1 -> node2 -> node3 -> None

Which sequence of pointer changes correctly reverses the list?

hard

A. Change each node's next pointer to the previous node, then update head to last node

B. Swap data values between nodes without changing pointers

C. Set head to None and create a new list with reversed data

D. Change each node's next pointer to None

Solution

1. Step 1: Understand reversal of singly linked list

   Reversing means changing each node's next pointer to point to the previous node instead of the next.

2. Step 2: Identify correct pointer update sequence

   Change each node's next pointer to the previous node, then update head to last node correctly describes reversing pointers and updating head to the last node. Swap data values between nodes without changing pointers only swaps data, not pointers. Set head to None and create a new list with reversed data discards the list unnecessarily. Change each node's next pointer to None breaks links without reversing.

3. Final Answer:

   Change each node's next pointer to the previous node, then update head to last node -> Option A

4. Quick Check:

   Reverse = reverse pointers + update head [OK]

Hint: Reverse pointers, then reset head to last node [OK]

Common Mistakes:

• Swapping data instead of pointers
• Not updating head after reversal
• Breaking links without reconnecting