Data structures is one of the most important concepts in computer science. They organize and store data efficiently, enabling us to perform operations such as insertion, deletion, and access more effectively. Common data structures are arrays, linked lists, stacks, queues, trees, and graphs. In this post, we will discuss 50 multiple-choice questions (MCQs) on data structures. These questions cover fundamental topics to help you strengthen your knowledge.
1. Which of the following data structures stores data in a linear manner?
- A) Stack
- B) Queue
- C) Array
- D) All of the above
Answer: D) All of the above
All of the listed data structures (stack, queue, and array) store data in a linear manner. They all organize data in a sequential format, with stack and queue also providing specific operations for managing data.
2. Which data structure is used for function calls in most programming languages?
- A) Queue
- B) Stack
- C) Tree
- D) Array
Answer: B) Stack
A stack is used to manage function calls in most programming languages. This is known as the “call stack,” where each function call is pushed onto the stack, and after the function finishes executing, it is popped off.
3. In a binary search tree (BST), what is the maximum number of nodes at level LLL?
- A) 2L2^L2L
- B) 2L−12^L – 12L−1
- C) 2L−12L – 12L−1
- D) L2L^2L2
Answer: A) 2L2^L2L
In a binary search tree, the maximum number of nodes at level LLL is 2L2^L2L. This is because at each level of a binary tree, the number of nodes doubles.
4. What is the time complexity of accessing an element in an array by index?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: A) O(1)O(1)O(1)
Accessing an element by index in an array is an O(1)O(1)O(1) operation, meaning it takes constant time regardless of the size of the array.
5. Which of the following is true about a doubly linked list?
- A) It can only be traversed in one direction.
- B) Each node has only one pointer to the next node.
- C) Each node has two pointers: one to the next node and one to the previous node.
- D) It cannot be used for deleting nodes.
Answer: C) Each node has two pointers: one to the next node and one to the previous node.
A doubly linked list allows traversal in both directions because each node contains two pointers: one pointing to the next node and one pointing to the previous node.
6. In a stack, which operation removes an element?
- A) Push
- B) Pop
- C) Peek
- D) Insert
Answer: B) Pop
The operation used to remove an element from a stack is called pop. It removes the top element from the stack.
7. Which of the following is the best data structure to implement a priority queue?
- A) Linked List
- B) Array
- C) Heap
- D) Stack
Answer: C) Heap
A heap is the best data structure for implementing a priority queue because it allows for efficient insertion and extraction of elements based on priority.
8. Which of the following is not a characteristic of a stack?
- A) Last In First Out (LIFO)
- B) Can only access the top element
- C) Allows random access
- D) Operates on a strict push and pop mechanism
Answer: C) Allows random access
In a stack, you can only access the top element, and random access is not allowed. This is in contrast to data structures like arrays or linked lists.
9. Which of the following operations is supported by a queue?
- A) Enqueue
- B) Dequeue
- C) Peek
- D) All of the above
Answer: D) All of the above
A queue supports three main operations: enqueue (add an element), dequeue (remove an element), and peek (view the front element).
10. What is the main difference between a binary tree and a binary search tree?
- A) Binary trees have only two child nodes.
- B) In binary search trees, the left child node’s value is greater than the parent node.
- C) In binary search trees, the left child node’s value is less than the parent node, and the right child node’s value is greater.
- D) Binary trees are balanced, but binary search trees are not.
Answer: C) In binary search trees, the left child node’s value is less than the parent node, and the right child node’s value is greater.
This is the defining property of binary search trees, which allows them to be used for efficient searching.
11. Which of the following is not a type of binary tree?
- A) Full Binary Tree
- B) Perfect Binary Tree
- C) Balanced Binary Tree
- D) Circular Binary Tree
Answer: D) Circular Binary Tree
A binary tree can be full, perfect, or balanced, but there is no such type as a circular binary tree.
12. Which data structure allows insertion and deletion of elements from both ends?
- A) Queue
- B) Stack
- C) Deque
- D) Array
Answer: C) Deque
A deque (double-ended queue) allows insertion and deletion of elements from both ends (front and rear).
13. Which of the following is used for searching an element in a hash table?
- A) Hash Function
- B) Binary Search
- C) Stack
- D) Array Index
Answer: A) Hash Function
A hash table uses a hash function to map keys to indices in an array, allowing for efficient searching of elements.
14. In a circular linked list, the last node points to:
- A) The first node
- B) Null
- C) Itself
- D) None of the above
Answer: A) The first node
In a circular linked list, the last node’s next pointer points back to the first node, creating a circle.
15. What is the time complexity for searching in a balanced binary search tree (BST)?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: C) O(logn)O(log n)O(logn)
In a balanced binary search tree, searching for an element takes O(logn)O(log n)O(logn) time because the tree is balanced, and at each step, half of the remaining nodes can be eliminated.
16. What is the space complexity of an array?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(n)O(n)O(n)
The space complexity of an array is O(n)O(n)O(n), where nnn is the number of elements stored in the array.
17. In a min-heap, the root node contains:
- A) The smallest element
- B) The largest element
- C) Any random element
- D) None of the above
Answer: A) The smallest element
In a min-heap, the root node contains the smallest element, and each parent node’s value is less than its children.
18. What is the purpose of a hash table?
- A) To store data in a sorted order
- B) To provide a fast lookup for elements based on keys
- C) To store data in a tree-like structure
- D) To organize elements in a queue
Answer: B) To provide a fast lookup for elements based on keys
Hash tables are designed for fast lookups by mapping keys to indices, providing constant time complexity for search, insert, and delete operations.
19. Which data structure is best suited for implementing an undo operation in an editor?
- A) Stack
- B) Queue
- C) Array
- D) Linked List
Answer: A) Stack
A stack is best suited for undo operations because it follows the Last In First Out (LIFO) principle, where the most recent operation is undone first.
20. What is the time complexity of accessing an element in a linked list by index?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(n)O(n)O(n)
In a linked list, accessing an element by index takes linear time, O(n)O(n)O(n), because you have to traverse the list from the beginning to reach the desired index.
21. What type of traversal is used to visit every node of a binary tree in the order: left child, parent, right child?
- A) Pre-order Traversal
- B) Post-order Traversal
- C) In-order Traversal
- D) Level-order Traversal
Answer: C) In-order Traversal
In in-order traversal, nodes are visited in the order: left child, parent, and right child.
22. Which operation is not possible in a queue?
- A) Enqueue
- B) Dequeue
- C) Random access
- D) Peek
Answer: C) Random access
In a queue, elements can only be added (enqueued) at the rear and removed (dequeued) from the front, and random access is not allowed.
23. Which of the following is true about a linked list?
- A) It allows direct access to elements by index.
- B) It is a dynamic data structure.
- C) It uses contiguous memory allocation.
- D) It is slower than arrays for sequential access.
Answer: B) It is a dynamic data structure.
A linked list is dynamic because it does not require contiguous memory. Nodes can be scattered throughout memory, and new nodes can be added or removed easily.
24. Which of the following is an example of a non-linear data structure?
- A) Array
- B) Linked List
- C) Tree
- D) Stack
Answer: C) Tree
A tree is a non-linear data structure because its elements (nodes) are arranged in a hierarchical manner, unlike arrays or linked lists, which are linear.
25. What is the worst-case time complexity for searching an element in an unsorted array?
- A) O(1)O(1)O(1)
- B) O(logn)O(log n)O(logn)
- C) O(n)O(n)O(n)
- D) O(n2)O(n^2)O(n2)
Answer: C) O(n)O(n)O(n)
In an unsorted array, searching for an element requires scanning through all the elements, which results in O(n)O(n)O(n) time complexity.
26. Which data structure is used to represent a tree?
- A) Linked List
- B) Stack
- C) Queue
- D) Array
Answer: A) Linked List
A tree is often represented using a linked list, where each node has a reference (or link) to its child nodes.
27. Which of the following operations takes constant time in a hash table?
- A) Insert
- B) Delete
- C) Search
- D) All of the above
Answer: D) All of the above
In a well-designed hash table, insert, delete, and search operations can all be performed in O(1)O(1)O(1) time on average.
28. What is the primary disadvantage of an array?
- A) It allows random access.
- B) It requires contiguous memory allocation.
- C) It is very fast.
- D) It is static in size.
Answer: B) It requires contiguous memory allocation.
Arrays require contiguous memory allocation, which can be inefficient if there is not enough consecutive space in memory to hold all elements.
29. Which of the following is true about a binary search tree?
- A) All left child nodes have values greater than the parent.
- B) All right child nodes have values greater than the parent.
- C) Both left and right child nodes must have the same value.
- D) It is always balanced.
Answer: B) All right child nodes have values greater than the parent.
In a binary search tree, the left child’s value is less than the parent’s value, and the right child’s value is greater.
30. What is the space complexity of a linked list?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(n)O(n)O(n)
The space complexity of a linked list is O(n)O(n)O(n), where nnn is the number of nodes because each node contains data and a pointer to the next node.
31. Which of the following is not a valid traversal technique for a tree?
- A) Pre-order
- B) In-order
- C) Post-order
- D) Level-order
Answer: D) Level-order
Level-order traversal is a valid traversal technique for a tree, but it is typically associated with breadth-first traversal, which is not commonly listed as a “traditional” tree traversal technique. However, all the listed techniques are widely used.
32. What is the time complexity of searching for an element in a balanced binary search tree (BST)?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(\log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: C) O(logn)O(\log n)O(logn)
In a balanced BST, the time complexity for searching for an element is O(logn)O(\log n)O(logn), as the tree’s height is minimized.
33. What type of data structure is a deque?
- A) Stack
- B) Queue
- C) Linked List
- D) Double-ended Queue
Answer: D) Double-ended Queue
A deque (double-ended queue) allows insertion and deletion of elements from both ends (front and rear), unlike a simple queue or stack.
34. Which of the following is not a characteristic of a priority queue?
- A) Elements are processed based on priority.
- B) It is implemented using a heap.
- C) It allows random access.
- D) Elements are inserted in arbitrary order.
Answer: C) It allows random access.
A priority queue does not allow random access to elements; elements are processed based on their priority rather than their position in the queue.
35. What is the advantage of a hash table over an array?
- A) Faster access
- B) Better space utilization
- C) Faster search and insertion operations
- D) Easier to implement
Answer: C) Faster search and insertion operations
A hash table provides faster search and insertion operations (typically O(1)O(1)O(1)) compared to an array (which takes O(n)O(n)O(n) time for search and insertion).
36. In which data structure can we perform insertion and deletion at both ends efficiently?
- A) Stack
- B) Queue
- C) Deque
- D) Array
Answer: C) Deque
A deque (double-ended queue) allows insertion and deletion of elements at both ends efficiently.
37. What is the worst-case time complexity of deleting an element from a binary search tree (BST)?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(logn)O(\log n)O(logn)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(n)O(n)O(n)
In the worst case (when the BST is unbalanced), deleting an element takes O(n)O(n)O(n) time, as it may require traversing the entire tree.
38. Which of the following is the main advantage of using a linked list over an array?
- A) Constant-time access
- B) Dynamic size allocation
- C) Better cache locality
- D) Less memory usage
Answer: B) Dynamic size allocation
Linked lists have dynamic size allocation, meaning they can grow and shrink as needed without the need for contiguous memory like an array.
39. Which data structure is most suitable for representing hierarchical relationships?
- A) Queue
- B) Stack
- C) Tree
- D) Graph
Answer: C) Tree
A tree is the most suitable data structure for representing hierarchical relationships, such as the structure of a directory or organizational chart.
40. Which of the following is true about a circular queue?
- A) The rear pointer always stays at the end of the queue.
- B) The queue uses a circular buffer, meaning the rear pointer can wrap around to the front.
- C) Dequeue operations are not allowed.
- D) It is a type of priority queue.
Answer: B) The queue uses a circular buffer, meaning the rear pointer can wrap around to the front.
In a circular queue, the rear pointer can wrap around when it reaches the end of the queue, making efficient use of the space.
41. Which of the following is an example of a linear data structure?
- A) Tree
- B) Graph
- C) Queue
- D) Hash Table
Answer: C) Queue
A queue is a linear data structure because its elements are arranged in a sequential order, and you can only access the front or rear elements.
42. What is the purpose of a binary heap?
- A) To maintain a balanced binary search tree
- B) To store data in a sorted order
- C) To implement a priority queue
- D) To represent a tree structure with minimal height
Answer: C) To implement a priority queue
A binary heap is used to implement a priority queue efficiently, where the highest (or lowest) priority element can be accessed in O(1)O(1)O(1) time.
43. Which data structure is used to represent a sparse matrix?
- A) Linked List
- B) Array
- C) Hash Table
- D) Linked List of Linked Lists
Answer: D) Linked List of Linked Lists
A sparse matrix can be represented using a linked list of linked lists, where each non-zero element is stored along with its row and column indices.
44. What does the term ‘overflow’ refer to in a stack?
- A) Adding more elements than the stack’s maximum capacity
- B) Removing elements from an empty stack
- C) Accessing elements in random order
- D) Reaching the middle of the stack
Answer: A) Adding more elements than the stack’s maximum capacity
Overflow occurs when more elements are pushed onto the stack than it can hold, exceeding its capacity.
45. What is a disadvantage of using a doubly linked list over a singly linked list?
- A) It requires more memory due to the extra pointer.
- B) It is slower to traverse.
- C) It cannot be used for circular lists.
- D) It cannot be used to store data in reverse order.
Answer: A) It requires more memory due to the extra pointer.
A doubly linked list requires extra memory for the additional pointer to the previous node, which increases space complexity.
46. In which of the following data structures can we efficiently implement a breadth-first search (BFS) algorithm?
- A) Stack
- B) Queue
- C) Binary Search Tree
- D) Array
Answer: B) Queue
Breadth-first search (BFS) is typically implemented using a queue, as it processes nodes in layers, visiting all neighbors before moving deeper into the graph.
47. Which of the following is the correct order of complexity for searching an element in an unsorted array?
- A) O(1)O(1)O(1)
- B) O(logn)O(log n)O(logn)
- C) O(n)O(n)O(n)
- D) O(n2)O(n^2)O(n2)
Answer: C) O(n)O(n)O(n)
In an unsorted array, searching for an element takes O(n)O(n)O(n) time, as you may need to check each element.
48. What is the correct time complexity of inserting an element in a heap?
- A) O(1)O(1)O(1)
- B) O(logn)O(log n)O(logn)
- C) O(n)O(n)O(n)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(logn)O(log n)O(logn)
Inserting an element into a heap takes O(logn)O(log n)O(logn) time, as the heap property may need to be restored by performing a series of swaps.
49. Which of the following traversal methods for a binary tree is used to obtain nodes in ascending order?
- A) Pre-order
- B) In-order
- C) Post-order
- D) Level-order
Answer: B) In-order
In-order traversal of a binary search tree (BST) visits the nodes in ascending order of their values.
50. What is the time complexity of merging two sorted linked lists into a single sorted linked list?
- A) O(1)O(1)O(1)
- B) O(n)O(n)O(n)
- C) O(nlogn)O(n \log n)O(nlogn)
- D) O(n2)O(n^2)O(n2)
Answer: B) O(n)O(n)O(n)
Merging two sorted linked lists takes O(n)O(n)O(n) time, as you only need to traverse each list once and compare elements to merge them.
This completes the set of 50 Data Structures MCQs! Let me know if you need more assistance or further explanations!
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