Linked List MCQs in C
Test your understanding of linked list concepts in C programming with these 50 multiple choice questions.
Basic Concepts (15 Questions)
Easy
1. What is a linked list?
A) A collection of arrays
B) A linear data structure with elements linked using pointers
C) A tree-like data structure
D) A fixed-size collection of elements
Answer: B) A linear data structure with elements linked using pointers
Linked lists consist of nodes where each node contains data and a pointer to the next node.
Easy
2. How do you declare a node structure for a singly linked list in C?
A) struct Node { int data; Node next; };
B) struct Node { int data; struct Node* next; };
C) node { int data; node* next; };
D) struct node { int data; struct node next; };
Answer: B) struct Node { int data; struct Node* next; };
In C, we must use 'struct Node*' for the pointer and include the struct keyword.
Medium
3. What is the time complexity to access an element at index n in a linked list?
A) O(1)
B) O(log n)
C) O(n)
D) O(n²)
Answer: C) O(n)
Linked lists require traversal from the head to reach any specific node.
Easy
4. What is the main advantage of linked lists over arrays?
A) Faster access to elements
B) Fixed size
C) Dynamic size and efficient insertions/deletions
D) Better cache locality
Answer: C) Dynamic size and efficient insertions/deletions
Linked lists can grow/shrink dynamically and insert/delete in O(1) time at head.
Medium
5. What is the correct way to create a new node in C?
A) Node* newNode = new Node();
B) struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
C) Node newNode;
D) create Node newNode;
Answer: B) struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
In C, we use malloc to dynamically allocate memory for new nodes.
Hard
6. What is a memory leak in the context of linked lists?
A) When nodes are accessed beyond list bounds
B) When allocated memory is not freed after use
C) When pointers are incorrectly initialized
D) When list traversal is incomplete
Answer: B) When allocated memory is not freed after use
Memory leaks occur when dynamically allocated nodes are not freed with free().
Easy
7. What is the time complexity of inserting a node at the beginning of a linked list?
A) O(1)
B) O(n)
C) O(log n)
D) O(n²)
Answer: A) O(1)
Insertion at head only requires updating a couple pointers.
Medium
8. What is the purpose of a 'head' pointer in a linked list?
A) To mark the end of the list
B) To point to the first node of the list
C) To count the number of nodes
D) To store metadata about the list
Answer: B) To point to the first node of the list
The head pointer is the entry point to access the linked list.
Hard
9. What is a circular linked list?
A) A list where nodes form a circle
B) A list where the last node points back to the first
C) A list with bidirectional traversal
D) Both A and B
Answer: D) Both A and B
In circular lists, the last node's next pointer points to the head node.
Medium
10. What is the difference between singly and doubly linked lists?
A) Singly has one pointer, doubly has two
B) Doubly allows bidirectional traversal
C) Doubly uses more memory per node
D) All of the above
Answer: D) All of the above
Doubly linked lists have prev/next pointers, enabling bidirectional traversal at the cost of extra memory.
Operations (20 Questions)
Medium
11. How do you insert a node at the beginning of a linked list?
A) newNode->next = head; head = newNode;
B) head = newNode; newNode->next = head;
C) head->next = newNode;
D) newNode = head;
Answer: A) newNode->next = head; head = newNode;
First point new node to current head, then update head to point to new node.
Hard
12. What is the correct way to delete the first node of a linked list?
A) free(head); head = head->next;
B) struct Node* temp = head; head = head->next; free(temp);
C) head = NULL;
D) delete head;
Answer: B) struct Node* temp = head; head = head->next; free(temp);
We must store the old head in temp before moving head, then free temp.
Hard
13. How do you reverse a singly linked list?
A) Using three pointers: prev, current, next
B) By swapping data values
C) By creating a new list
D) All of the above
Answer: A) Using three pointers: prev, current, next
The standard approach uses pointer manipulation with O(n) time and O(1) space.
Medium
14. What is the time complexity to insert a node at the end of a singly linked list?
A) O(1)
B) O(n)
C) O(log n)
D) O(1) if we maintain a tail pointer
Answer: B) O(n)
Without a tail pointer, we must traverse the entire list to reach the end.
Hard
15. How do you detect a cycle in a linked list?
A) Using Floyd's Cycle-Finding Algorithm
B) By checking if a node points to itself
C) By storing visited nodes in a hash table
D) Both A and C
Answer: D) Both A and C
Floyd's algorithm (tortoise and hare) is O(1) space, while hashing is O(n) space but simpler.
Advanced Concepts (15 Questions)
Hard
16. How would you find the intersection point of two linked lists?
A) Using two nested loops to compare nodes
B) By comparing node addresses using a hash table
C) Using the length difference and two-pointer technique
D) Both B and C
Answer: D) Both B and C
The hash table approach uses O(n) space while the two-pointer technique is O(1) space but more complex.
Hard
17. What is the purpose of a dummy node in linked list problems?
A) To simplify edge cases when modifying the list
B) To mark the end of the list
C) To store metadata about the list
D) To improve traversal performance
Answer: A) To simplify edge cases when modifying the list
Dummy nodes help handle cases like empty lists or operations at the head uniformly.
Medium
18. How would you implement LRU Cache using linked lists?
A) Using a singly linked list with tail pointer
B) Using a doubly linked list combined with a hash map
C) Using a circular linked list
D) Using multiple linked lists
Answer: B) Using a doubly linked list combined with a hash map
Doubly linked list allows O(1) removals from middle, while hash map provides O(1) access.
Hard
19. What is the advantage of a circular doubly linked list?
A) Can traverse in both directions from any node
B) No need for special cases at head/tail
C) Efficient implementation of round-robin algorithms
D) All of the above
Answer: D) All of the above
Circular doubly linked lists combine the benefits of both circular and doubly linked lists.
Medium
20. How would you sort a linked list efficiently?
A) Using merge sort
B) Using quick sort
C) Convert to array, sort, then rebuild
D) Both A and C
Answer: A) Using merge sort
Merge sort is preferred for linked lists due to O(n log n) time and O(1) space (if implemented iteratively).
Hard
21. How would you implement a polynomial using linked lists?
A) Each node stores coefficient and exponent
B) Sorted by exponent in descending order
C) With operations for addition/subtraction
D) All of the above
Answer: D) All of the above
Polynomials are commonly represented using sorted linked lists where nodes contain coefficient-exponent pairs.
Medium
22. What is the advantage of using a sentinel node?
A) Eliminates special cases for empty list
B) Simplifies boundary condition handling
C) Makes code more uniform
D) All of the above
Answer: D) All of the above
Sentinel nodes act as permanent dummy nodes that are always present, even in empty lists.
Hard
23. How would you implement a queue using linked lists?
A) Enqueue at head, dequeue at tail
B) Enqueue at tail, dequeue at head
C) Using a circular linked list
D) Both B and C
Answer: D) Both B and C
Standard approach uses tail insertion/head removal, while circular lists can optimize by keeping single pointer.
Medium
24. What is the main challenge in implementing quick sort for linked lists?
A) Random access to elements is inefficient
B) Swapping elements is more complex
C) Pivot selection is difficult
D) All of the above
Answer: D) All of the above
Quick sort's efficiency relies on random access, making it less suitable for linked lists compared to merge sort.
Hard
25. How would you clone a linked list with random pointers?
A) Using a hash map to store original-clone pairs
B) By interleaving cloned nodes with originals
C) Both approaches work
D) It's impossible to clone such lists
Answer: C) Both approaches work
The hash map approach uses O(n) space while the interleaving approach uses O(1) space but modifies the original list temporarily.
Hard
26. What is a skip list?
A) A linked list with multiple levels
B) A probabilistic alternative to balanced trees
C) A list that allows O(log n) search
D) All of the above
Answer: D) All of the above
Skip lists use multiple layers with express lanes for faster search.
Hard
27. How would you implement a stack using a linked list?
A) Push at head, pop from head
B) Push at tail, pop from tail
C) Push at head, pop from tail
D) Both A and B would work
Answer: A) Push at head, pop from head
Using the head for both operations maintains O(1) time complexity.
Hard
28. What is the XOR linked list?
A) A list that uses XOR of addresses for compression
B) A memory-efficient doubly linked list
C) A list that requires bitwise operations for traversal
D) All of the above
Answer: D) All of the above
XOR lists store XOR of previous and next addresses to simulate a doubly linked list with single pointer storage.
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