Commonly Asked Data Structure Interview Questions on Queue

Question 1: What is a Queue?

Answer: A queue is a linear data structure that follows the First-In-First-Out (FIFO) principle, where elements are added at the rear (enqueue) and removed from the front (dequeue).

Question 2: What are the different types of Queues?

Answer:

Question 3: How is a Queue implemented in an array?

Answer: An array can be used to implement a simple queue by maintaining two pointers: front and rear. Front points to the first element, and rear points to the next available position.

Question 4: How is a Queue implemented in a linked list?

Answer: A linked list can be used to implement a queue by creating a node for each element and maintaining a head and tail pointer. Enqueueing adds a node to the tail, and dequeueing removes a node from the head.

Question 5: What is the time complexity of enqueue and dequeue operations in a Queue?

Answer:

Enqueue: O(1)
Dequeue: O(1) for simple and circular queues, O(n) for priority queues

Question 6: What is the difference between a Queue and a Stack?

Answer: A queue follows FIFO, while a stack follows Last-In-First-Out (LIFO).

Question 7: What are the applications of Queues?

Answer:

Task scheduling
Message passing
Simulation of real-world scenarios

Question 8: How do you handle overflow and underflow conditions in a Queue?

Answer:

Overflow: When the queue is full, throw an exception or return an error code.
Underflow: When the queue is empty, throw an exception or return a null value.

Question 9: What is a circular queue?

Answer: A circular queue is a variation of a simple queue where the rear pointer wraps around to the beginning of the array after reaching the end.

Question 10: What is a priority queue?

Answer: A priority queue is a queue where elements are assigned priorities and are dequeued based on their priorities.

Question 11: How is a priority queue implemented?

Answer: Priority queues can be implemented using a binary heap or a self-balancing binary search tree.

Question 12: What is a double-ended queue (Deque)?

Answer: A deque is a queue that allows insertions and deletions from both ends.

Question 13: How is a deque implemented?

Answer: A deque can be implemented using two stacks or a circular buffer.

Question 14: What are the advantages of using a Queue?

Answer:

Simple and efficient FIFO implementation
Easy to enqueue and dequeue elements
Supports multiple producers and consumers

Question 15: What are the disadvantages of using a Queue?

Answer:

Limited access to elements (only from the front or rear)
Can be inefficient if elements need to be accessed in a non-sequential order