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DS Stacks & Queues: 17 MCQs with answers

All 17 multiple-choice questions from this kit, free and with no sign-up.

Full kit · everything

Warm-up · 8 questions

Q1. Which data structure follows the Last-In-First-Out (LIFO) principle?

Beginner
A Queue B Linked List C Tree D Stack
Show answer & explanation

Stack

A stack processes the most recently added element first, which is the LIFO principle.

Q2. In a queue, which operation removes an element?

Beginner
A pop B dequeue C enqueue D push
Show answer & explanation

dequeue

Dequeue removes the front element from a queue, while enqueue adds to the rear.

Q3. What is the primary difference between a stack and a queue?

Beginner
A Both are LIFO B Both are FIFO C Stack is LIFO, queue is FIFO D Stack is FIFO, queue is LIFO
Show answer & explanation

Stack is LIFO, queue is FIFO

Stack follows Last-In-First-Out, while queue follows First-In-First-Out.

Q4. Which operation adds an element to the rear of a queue?

Beginner
A pop B enqueue C push D dequeue
Show answer & explanation

enqueue

Enqueue adds an element to the rear of a queue.

Q5. Which of the following is NOT a valid operation on a stack?

Beginner
A peek B enqueue C push D pop
Show answer & explanation

enqueue

Enqueue is an operation for queues, not stacks.

Q6. In a stack, which element is accessible?

Beginner
A The middle element B The bottom element C Any element D The top element
Show answer & explanation

The top element

Only the top element of a stack is directly accessible.

Q7. A stack allows insertion and deletion at both ends.

Beginner
A True B False
Show answer & explanation

False

A stack allows insertion and deletion only at one end, called the top.

Q8. A queue follows the First-In-First-Out (FIFO) principle.

Beginner
A True B False
Show answer & explanation

True

A queue processes elements in the order they were added, which is FIFO.

Building up · 6 questions

Q9. What is the time complexity of the push operation on a stack implemented as a linked list?

Intermediate
A $O(1)$ B $O(n^2)$ C $O(\log n)$ D $O(n)$
Show answer & explanation

$O(1)$

Pushing onto a linked-list stack adds a node at the head, which takes constant time.

Q10. Which of the following applications typically uses a stack?

Intermediate
A CPU scheduling B Function call management C Print spooling D Breadth-first search
Show answer & explanation

Function call management

Stacks are used to manage function calls, including return addresses and local variables.

Q11. What is the time complexity of the pop operation on a stack implemented as an array?

Intermediate
A $O(n)$ B $O(n^2)$ C $O(1)$ D $O(\log n)$
Show answer & explanation

$O(1)$

Popping from an array-based stack removes the top element, which is a constant-time operation.

Q12. Which data structure is used in breadth-first search (BFS) of a graph?

Intermediate
A Set B Priority Queue C Stack D Queue
Show answer & explanation

Queue

BFS uses a queue to explore nodes level by level.

Q13. What is the time complexity of the dequeue operation on a queue implemented as a linked list?

Intermediate
A $O(n)$ B $O(n^2)$ C $O(\log n)$ D $O(1)$
Show answer & explanation

$O(1)$

Dequeue removes the front node, which takes constant time in a linked-list queue.

Q14. Which application uses a queue?

Intermediate
A Function call stack B Undo operation in editors C Expression evaluation D Printer spooling
Show answer & explanation

Printer spooling

Printer spooling uses a queue to manage print jobs in order.

Topper level · 3 questions

Q15. In a circular queue of capacity $n$, what is the condition for a full queue when using a front and rear index?

Advanced
A $front = 0$ B $front = rear$ C $(rear + 1) \% n = front$ D $rear = n - 1$
Show answer & explanation

$(rear + 1) \% n = front$

A circular queue is full when the next position of rear would be front.

Q16. What is the condition for an empty queue when using front and rear indices?

Advanced
A $rear = n - 1$ B $front = rear + 1$ C $front = 0$ D $front = rear$
Show answer & explanation

$front = rear$

An empty queue is typically indicated when front equals rear.

Q17. What is the time complexity of the enqueue operation on a circular queue implemented as an array?

Advanced
A $O(1)$ B $O(n)$ C $O(n^2)$ D $O(\log n)$
Show answer & explanation

$O(1)$

Enqueue in a circular queue adds an element at the rear and updates the rear index, which is constant time.

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