Stacks & Queues: 20 Essential Interview Questions & Answers

stack and Queue

Stacks and Queues are fundamental data structures in computer science and are widely used in problem-solving and system design. This article presents 20 essential interview questions and detailed answers to help you prepare for coding interviews.

Stack (LIFO — Last In, First Out)

Stack

1. What is a Stack?

A stack is a linear data structure that follows the Last In, First Out (LIFO) principle. Elements are added (pushed) and removed (popped) only from the top of the stack.

2. What are the primary operations of a Stack?

• Push(x): Inserts element x at the top.
• Pop(): Removes the top element.
• Peek()/Top(): Returns the top element without removing it.
• isEmpty(): Checks if the stack is empty.
• isFull(): Checks if the stack is full (in the case of the fixed-size stack).

3. How can a Stack be implemented?