DSA looks hard to practice, but it is the skill companies always ask for in interviews, especially those MNCs. Data Structures and Algorithms form the foundation of coding interviews because they help companies evaluate your problem-solving ability, which is super necessary for software development jobs.
If you want to check your preparation before the interview, start with this DSA quiz set. These 100 DSA MCQs will test your DSA skills and help you decide if you are ready for the interview or if you need more preparation.
Learn DSA Step-by-Step with 100 DSA MCQ
Practising DSA MCQs is one of the best ways to test your problem-solving skills. With multiple-choice options, you are forced to think again and again, compare choices, and then select the best answer.
Read each DSA quiz first and try to answer it yourself, then only click the dropdown button next to each question to find the correct answer and explanation.
Q1. Which data structure uses FIFO (First In First Out) principle?
A. Stack
B. Queue
C. Tree
D. Graph
Show Answer
Answer: B
Queue operates on FIFO principle, where the first element added is the first removed.
Q2. What is the time complexity of accessing an element in an array by index?
A. O(n)
B. O(log n)
C. O(1)
D. O(n log n)
Show Answer
Answer: C
Direct indexing in an array takes constant time O(1).
Q3. In a linked list, what is the time complexity to insert at the beginning?
A. O(1)
B. O(n)
C. O(log n)
D. O(n²)
Show Answer
Answer: A
Inserting at the head of a linked list takes constant time.
Q4. Which of the following sorting algorithms has the best average-case time complexity?
A. Bubble Sort
B. Insertion Sort
C. Quick Sort
D. Selection Sort
Show Answer
Answer: C
Quick Sort has an average-case time complexity of O(n log n).
Q5. What is the main advantage of a binary search tree (BST)?
A. Fast insertion only
B. No need for sorting
C. Quick search, insert, delete if balanced
D. Uses less memory than arrays
Show Answer
Answer: C
A balanced BST offers efficient search, insert, delete in O(log n).
Q6. Which data structure uses LIFO (Last In First Out)?
A. Queue
B. Stack
C. Tree
D. Heap
Show Answer
Answer: B
Stack follows LIFO, where the last added is first removed.
Q7. What is the height of a complete binary tree with N nodes in the worst case?
A. O(1)
B. O(n)
C. O(log n)
D. O(n log n)
Show Answer
Answer: C
Height of a complete binary tree is O(log n).
Q8. Which data structure is best suited for implementing recursion?
A. Queue
B. Stack
C. Array
D. Tree
Show Answer
Answer: B
Recursion uses a call stack internally.
Q9. What is the best-case time complexity of linear search?
A. O(n)
B. O(log n)
C. O(1)
D. O(n²)
Show Answer
Answer: C
If the element is at first position, linear search is O(1).
Q10. In hashing, what does collision refer to?
A. Two keys map to different buckets
B. Two keys map to the same bucket
C. No key found
D. Table overflow
Show Answer
Answer: B
Collision is when two keys hash to the same index.
Q11. What is the space complexity of merge sort?
A. O(1)
B. O(n)
C. O(log n)
D. O(n log n)
Show Answer
Answer: B
Merge sort requires additional array space of O(n).
Q12. Which traversal visits nodes in the order: left, root, right?
A. Preorder
B. Inorder
C. Postorder
D. Level Order
Show Answer
Answer: B
Inorder traversal follows left-root-right.
Q13. What is the worst-case time complexity of quick sort?
A. O(n)
B. O(n log n)
C. O(n²)
D. O(log n)
Show Answer
Answer: C
Worst-case occurs when pivot is poorly chosen.
Q14. Which data structure is suitable for BFS (Breadth First Search)?
A. Stack
B. Queue
C. Hash Table
D. Tree
Show Answer
Answer: B
BFS uses a queue to track nodes level-wise.
Q15. In an array of size n, what is the index of last element (0-based)?
A. n
B. 1
C. n-1
D. n+1
Show Answer
Answer: C
0-based indexing ends at n-1.
Q16. A balanced binary tree ensures…
A. Same number of left and right nodes
B. Height difference <= 1 for subtrees
C. All nodes have two children
D. Only leaf nodes at last level
Show Answer
Answer: B
Balanced tree keeps height differences minimal.
Q17. Which algorithm is used to find the shortest path in a weighted graph?
A. DFS
B. BFS
C. Dijkstra’s Algorithm
D. Quick Sort
Show Answer
Answer: C
Dijkstra finds shortest paths in weighted graphs.
Q18. What data structure is used in priority queue?
A. Stack
B. Heap
C. Queue
D. Array
Show Answer
Answer: B
Heap provides efficient priority queue operations.
Q19. Which is NOT a stable sorting algorithm?
A. Bubble Sort
B. Merge Sort
C. Quick Sort
D. Insertion Sort
Show Answer
Answer: C
Quick Sort is not stable by default.
Q20. What is the time complexity of binary search?
A. O(n)
B. O(log n)
C. O(n log n)
D. O(1)
Show Answer
Answer: B
Binary search halves the search space each step.
Q21. In a graph, an edge connecting a vertex to itself is called?
A. Loop
B. Bridge
C. Cycle
D. Path
Show Answer
Answer: A
A loop is an edge from vertex to itself.
Q22. Which is used to detect cycles in a graph?
A. BFS
B. DFS
C. Quick Sort
D. Merge Sort
Show Answer
Answer: B
DFS helps in cycle detection using recursion/stack.
Q23. What is the purpose of a sentinel in data structures?
A. Speed up search
B. Indicate end of structure
C. Store max value
D. Encrypt data
Show Answer
Answer: B
Sentinel marks boundaries or end of structure.
Q24. Which sort has best performance on nearly sorted data?
A. Quick Sort
B. Bubble Sort
C. Insertion Sort
D. Heap Sort
Show Answer
Answer: C
Insertion sort works well on nearly sorted data.
Q25. What is the main purpose of hashing?
A. Sort elements
B. Search efficiently
C. Store duplicates only
D. Remove items
Show Answer
Answer: B
Hashing enables fast search and retrieval.
Q26. What is the worst-case time complexity of searching in a binary search tree (BST)?
A. O(1)
B. O(log n)
C. O(n)
D. O(n log n)
Show Answer
Answer: C
In the worst case of a skewed BST, search costs O(n).
Q27. Which data structure is best for implementing undo functionality in applications?
A. Queue
B. Stack
C. Linked List
D. Hash Table
Show Answer
Answer: B
Stack stores states and supports undo with LIFO order.
Q28. Which algorithm is commonly used for sorting that always guarantees O(n log n) time complexity?
A. Quick Sort
B. Merge Sort
C. Bubble Sort
D. Insertion Sort
Show Answer
Answer: B
Merge sort consistently runs in O(n log n).
Q29. In a hash table, what does the load factor measure?
A. Number of hash functions used
B. Ratio of number of elements to bucket size
C. Time to insert an element
D. Total number of collisions
Show Answer
Answer: B
Load factor = number of entries / number of buckets.
Q30. What is the best-case complexity of bubble sort?
A. O(n²)
B. O(n log n)
C. O(n)
D. O(1)
Show Answer
Answer: C
If already sorted, it takes O(n) with optimization.
Q31. Which traversal of a binary tree prints nodes level by level?
A. Inorder
B. Preorder
C. Postorder
D. Level Order
Show Answer
Answer: D
Level order uses BFS to visit tree levels.
Q32. In a dynamic array, what happens when the capacity is full and a new element is added?
A. It throws error
B. It resizes to a larger array
C. It deletes the first element
D. It stays same size
Show Answer
Answer: B
Dynamic arrays resize (often double) when full.
Q33. What is the time complexity to insert an element in a max-heap?
A. O(1)
B. O(log n)
C. O(n)
D. O(n log n)
Show Answer
Answer: B
Insertion in heap takes O(log n) to restore heap property.
Q34. Which algorithm finds the shortest path in a graph with non-negative weights?
A. Bellman-Ford
B. Depth First Search
C. Dijkstra’s Algorithm
D. Kruskal’s Algorithm
Show Answer
Answer: C
Dijkstra’s works on non-negative weighted graphs.
Q35. Which of these is not a divide and conquer algorithm?
A. Quick Sort
B. Merge Sort
C. Binary Search
D. Bubble Sort
Show Answer
Answer: D
Bubble sort is not divide and conquer.
Q36. What data structure is primarily used to implement recursion?
A. Queue
B. Stack
C. Hash Map
D. Tree
Show Answer
Answer: B
The call stack manages function calls in recursion.
Q37. Which algorithm technique avoids recomputation by storing results of subproblems?
A. Greedy
B. Dynamic Programming
C. Divide and Conquer
D. Backtracking
Show Answer
Answer: B
Dynamic programming stores subproblem results.
Q38. In BFS traversal of a graph, which data structure is used?
A. Stack
B. Queue
C. Priority Queue
D. Hash Set
Show Answer
Answer: B
BFS uses queue to visit nodes level-wise.
Q39. What is the key property of a min-heap?
A. Parent greater than children
B. Parent less than children
C. Equal values at all nodes
D. Sorted order of elements
Show Answer
Answer: B
In a min-heap, parent ≤ children.
Q40. What is the time complexity of finding the maximum element in an unsorted array?
A. O(1)
B. O(log n)
C. O(n)
D. O(n log n)
Show Answer
Answer: C
Must scan all elements for max in unsorted array.
Q41. Which of these is a self-balancing BST?
A. Red-Black Tree
B. Binary Tree
C. Linked List
D. Heap
Show Answer
Answer: A
Red-Black is a self-balancing BST.
Q42. What search technique requires a sorted array?
A. Linear Search
B. Binary Search
C. Hash Search
D. Graph Search
Show Answer
Answer: B
Binary search works on sorted arrays.
Q43. Which data structure supports both stack and queue operations efficiently?
A. Linked List
B. Deque
C. Heap
D. Tree
Show Answer
Answer: B
Deque supports operations at both ends.
Q44. What is the purpose of a sentinel node in a linked list?
A. Store max value
B. Indicate beginning or end
C. Store count of nodes
D. Improve sorting
Show Answer
Answer: B
Sentinel marks boundaries in a list.
Q45. What is the main advantage of using a balanced tree?
A. Uses more memory
B. Faster insert, delete, search
C. Easier to code
D. Slower traversal
Show Answer
Answer: B
Balanced trees optimize operations.
Q46. Which data structure can provide constant time complexity for insertion and average constant time for search?
A. Array
B. Hash Table
C. Stack
D. Linked List
Show Answer
Answer: B
Hash tables use hashing to allow average O(1) insert and search.
Q47. Which traversal technique visits nodes in the order: root, left, right?
A. Inorder
B. Postorder
C. Preorder
D. Level Order
Show Answer
Answer: C
Preorder traversal visits root before children.
Q48. What is the result of applying binary search on an unsorted array?
A. Fastest search
B. Correct result always
C. Incorrect or undefined
D. Finds first element
Show Answer
Answer: C
Binary search requires a sorted array to work correctly.
Q49. Which of these sorting algorithms is in place and stable?
A. Bubble Sort
B. Quick Sort
C. Merge Sort
D. Heap Sort
Show Answer
Answer: A
Bubble sort is both in-place and stable.
Q50. In graph terminology, what is degree of a vertex?
A. Number of connected components
B. Distance from root
C. Number of edges incident to it
D. Number of nodes
Show Answer
Answer: C
The degree equals the count of connected edges.
Q51. Which algorithm is used to find minimum spanning tree in a weighted graph?
A. Dijkstra’s
B. Floyd-Warshall
C. Kruskal’s
D. Binary Search
Show Answer
Answer: C
Kruskal’s algorithm finds MST by sorting edges.
Q52. What data structure allows insertion and deletion from both ends?
A. Stack
B. Queue
C. Deque
D. Tree
Show Answer
Answer: C
Deque supports operations at front and rear ends.
Q53. Which algorithm design paradigm solves problems by combining optimal solutions of subproblems?
A. Greedy
B. Dynamic Programming
C. Brute Force
D. Backtracking
Show Answer
Answer: B
Dynamic programming uses optimal substructure.
Q54. What type of tree is a max heap?
A. Binary Search Tree
B. Balanced Binary Tree
C. Complete Binary Tree
D. AVL Tree
Show Answer
Answer: C
Heaps are complete binary trees with heap property.
Q55. Which is fastest search method for sorted data?
A. Linear Search
B. Binary Search
C. Hash Search
D. BFS
Show Answer
Answer: B
Binary search divides sorted data for fast search.
Q56. In a circular queue, what happens when rear is just before front?
A. Overflow
B. Underflow
C. Full queue
D. Empty queue
Show Answer
Answer: C
Circular queue is full when rear is just behind front.
Q57. Which complexity is used to measure algorithm performance growth relative to input?
A. Space Complexity
B. Time Complexity
C. Weight Complexity
D. Load Factor
Show Answer
Answer: B
Time complexity measures growth with input size.
Q58. Which of these is NOT a linear data structure?
A. Stack
B. Queue
C. Tree
D. Array
Show Answer
Answer: C
Tree is a non-linear data structure.
Q59. What does a priority queue use internally to achieve ordering?
A. Array sort
B. Heap
C. Linked List
D. Queue
Show Answer
Answer: B
Priority queues use heaps for efficient order.
Q60. Which operation on a stack removes the top element?
A. Push
B. Pop
C. Enqueue
D. Dequeue
Show Answer
Answer: B
Pop removes top element from a stack.
Q61. What is the purpose of recursion in algorithms?
A. Loop optimization
B. Divide a problem into subproblems
C. Sorting data
D. Allocating memory
Show Answer
Answer: B
Recursion solves problems via subproblem breakdown.
Q62. In merge sort, how many subarrays is the array divided into?
A. 2
B. 3
C. n
D. log n
Show Answer
Answer: A
Merge sort uses divide-and-conquer by splitting into two.
Q63. Which of these is a non-linear data structure used for hierarchical relations?
A. Array
B. Linked List
C. Tree
D. Stack
Show Answer
Answer: C
Trees represent hierarchical structures.
Q64. What does BFS stand for in graph traversal?
A. Binary First Search
B. Breadth First Search
C. Best First Search
D. Backward First Search
Show Answer
Answer: B
BFS explores neighbors level by level.
Q65. Which sorting algorithm repeatedly swaps adjacent elements?
A. Heap Sort
B. Quick Sort
C. Bubble Sort
D. Bucket Sort
Show Answer
Answer: C
Bubble sort swaps adjacent elements repeatedly.
Q66. What is the worst-case time complexity of linear search?
A. O(log n)
B. O(n)
C. O(1)
D. O(n log n)
Show Answer
Answer: B
Linear search may check all elements.
Q67. Which data structure uses pointers to connect nodes?
A. Stack
B. Tree
C. Linked List
D. Array
Show Answer
Answer: C
Linked lists connect nodes via pointers.
Q68. What is the key property of a BST (Binary Search Tree)?
A. All nodes have two children
B. Left child < parent < right child
C. Perfectly balanced
D. No duplicates allowed
Show Answer
Answer: B
BST stores less values left and greater right.
Q69. Which algorithm is used to find shortest path from one source to all nodes?
A. Bellman-Ford
B. Quick Sort
C. DFS
D. Heap Sort
Show Answer
Answer: A
Bellman-Ford finds shortest paths even with negative weights.
Q70. What is the auxiliary space complexity of quick sort in average case?
A. O(1)
B. O(log n)
C. O(n)
D. O(n log n)
Show Answer
Answer: B
Quick sort uses stack space of O(log n) on average.
Q71. What is the worst-case time complexity to insert in a hash table (without resizing)?
A. O(1)
B. O(n)
C. O(log n)
D. O(n log n)
Show Answer
Answer: B
In the worst case (many collisions), insertion can degrade to O(n).
Q72. Which graph traversal algorithm uses a queue?
A. DFS
B. BFS
C. Dijkstra’s
D. Bellman-Ford
Show Answer
Answer: B
BFS uses a queue to explore neighbors level by level.
Q73. Which property defines a complete binary tree?
A. Every node has two children
B. All levels except last are full
C. Left subtree is bigger than right
D. Sorted order of nodes
Show Answer
Answer: B
Complete binary tree has all levels full except possibly the last.
Q74. What is the time complexity of insertion sort in best case?
A. O(n²)
B. O(n)
C. O(1)
D. O(log n)
Show Answer
Answer: B
If data is nearly sorted, insertion sort runs in O(n).
Q75. Which algorithm finds shortest path in unweighted graph?
A. DFS
B. BFS
C. Dijkstra’s
D. Prim’s
Show Answer
Answer: B
BFS finds the shortest path by level.
Q76. Which of these is a non-recursive sort?
A. Quick Sort
B. Merge Sort
C. Insertion Sort
D. Binary Search
Show Answer
Answer: C
Insertion sort is iterative and non-recursive.
Q77. What is the worst-case complexity of selection sort?
A. O(n)
B. O(n log n)
C. O(n²)
D. O(log n)
Show Answer
Answer: C
Selection sort always performs O(n²) steps.
Q78. Which data structure best supports FIFO operations?
A. Stack
B. Queue
C. Heap
D. Graph
Show Answer
Answer: B
Queue enforces first-in, first-out behavior.
Q79. What is the height of a binary search tree in balanced best case?
A. O(n)
B. O(log n)
C. O(1)
D. O(n log n)
Show Answer
Answer: B
Balanced BST has height O(log n).
Q80. Which algorithm finds MST (Minimum Spanning Tree)?
A. Dijkstra’s
B. BFS
C. Bellman-Ford
D. Prim’s
Show Answer
Answer: D
Prim’s algorithm finds the MST.
Q81. Which structure allows O(1) access by key?
A. Linked List
B. Hash Table
C. Binary Tree
D. Matrix
Show Answer
Answer: B
Hash tables allow average O(1) access by key.
Q82. Which sorting technique repeatedly selects minimum element?
A. Bubble Sort
B. Selection Sort
C. Quick Sort
D. Heap Sort
Show Answer
Answer: B
Selection sort picks the minimum each round.
Q83. What does adjacency matrix represent in a graph?
A. List of neighbors
B. Matrix of edges
C. Sorted vertices
D. Priority order
Show Answer
Answer: B
Adjacency matrix stores edges in a 2D matrix.
Q84. Which algorithm has average time O(n log n) for sorting?
A. Heap Sort
B. Quick Sort
C. Merge Sort
D. All of the above
Show Answer
Answer: D
Heap, Quick, and Merge all run on average O(n log n).
Q85. What is the space complexity of stack using array?
A. O(1)
B. O(n)
C. O(log n)
D. O(n log n)
Show Answer
Answer: B
Array stack uses O(n) space for n elements.
Q86. Which sort algorithm uses divide and conquer?
A. Bubble Sort
B. Quick Sort
C. Linear Search
D. Hashing
Show Answer
Answer: B
Quick sort divides problem into subproblems.
Q87. What type of graph has no cycles?
A. Cyclic Graph
B. Acyclic Graph
C. Complete Graph
D. Weighted Graph
Show Answer
Answer: B
Acyclic graph has no cycles.
Q88. In an array, what is the index of first element (0-based)?
A. 1
B. 0
C. n-1
D. -1
Show Answer
Answer: B
0-based arrays start at index 0.
Q89. Which search moves one step at a time?
A. Binary Search
B. Linear Search
C. Hash Search
D. Heap Search
Show Answer
Answer: B
Linear search checks one by one.
Q90. What is the worst case of quick sort?
A. O(n)
B. O(n log n)
C. O(n²)
D. O(1)
Show Answer
Answer: C
Poor pivot choices lead to O(n²).
Q91. Which tree traversal prints sorted nodes for BST?
A. Preorder
B. Inorder
C. Postorder
D. Level-Order
Show Answer
Answer: B
Inorder traversal gives sorted BST output.
Q92. Which heap always has the largest element at root?
A. Min-Heap
B. Max-Heap
C. BST
D. AVL Tree
Show Answer
Answer: B
Max-heap root stores the largest key.
Q93. What is the linear search time if element not found?
A. O(1)
B. O(log n)
C. O(n)
D. O(n²)
Show Answer
Answer: C
Linear search may scan entire array.
Q94. What is the space complexity of merge sort?
A. O(1)
B. O(n)
C. O(log n)
D. O(n log n)
Show Answer
Answer: B
Merge sort needs O(n) extra space.
Q95. Which data structure stores parent-child relationships?
A. Stack
B. Tree
C. Hash Table
D. Queue
Show Answer
Answer: B
Trees represent parent and child linkage.
Q96. Which operation in a hash table is most affected by poor hash function quality?
A. Sorting
B. Searching
C. Traversal
D. Memory allocation
Show Answer
Answer: B
A bad hash function increases collisions and slows search operations.
Q97. What is the typical time complexity for inserting into a balanced BST like AVL tree?
A. O(1)
B. O(log n)
C. O(n)
D. O(n log n)
Show Answer
Answer: B
Balanced BSTs maintain height so insertion stays O(log n).
Q98. In a graph, what does DFS stand for?
A. Dynamic Function Search
B. Depth First Search
C. Data Flow Sort
D. Directed Fast Scan
Show Answer
Answer: B
DFS explores as far as possible along each branch before backtracking.
Q99. Which of these is NOT a hashing collision resolution technique?
A. Separate chaining
B. Open addressing
C. Linear probing
D. Binary search
Show Answer
Answer: D
Binary search is unrelated to resolving hash collisions.
Q100. What is the purpose of the ‘parent’ pointer in a union-find (disjoint set) data structure?
A. To sort elements
B. To find the root representative
C. To track element frequency
D. To balance trees
Show Answer
Answer: B
Parent pointers help locate the set’s representative element.
Conclusion
So, how many questions did you answer correctly? You might not have been able to answer many of them, but simply by reviewing the answers and explanations, you’ll be able to answer them next time. You can practice each of these 100 DSA MCQs two or three times a week, and when you feel confident that you can not only answer all of them but also understand the concepts behind them, then you’re ready to go.
Interested in DSA with Python? Check out: Python Data Structures
Resources and References:
- https://stackoverflow.com/questions/tagged/data-structures — Stack Overflow Data Structures tag with real programmer questions and answers about DSA concepts.
- https://www.reddit.com/r/datastructures/ — Reddit r/datastructures community for discussions, tips, and help on data structure and algorithm learning.
