What is a stack and how is it different from a queue?

A stack and a queue are both abstract data types used in computer science to store and organize data. They have different characteristics and are used in different scenarios.

A stack is a linear data structure that follows the Last-In-First-Out (LIFO) principle. It can be visualized as a stack of plates, where the last plate added is the first one to be removed. In a stack, elements are added and removed from the same end, known as the top of the stack. The operations performed on a stack are:

1. Push: Adds an element to the top of the stack.
2. Pop: Removes the top element from the stack.
3. Peek: Returns the value of the top element without removing it.
4. IsEmpty: Checks if the stack is empty.

Stacks are commonly used in scenarios where the order of processing is important, such as function calls, expression evaluation, and backtracking algorithms. The most common implementation of a stack is using an array or a linked list.

On the other hand, a queue is a linear data structure that follows the First-In-First-Out (FIFO) principle. It can be visualized as a queue of people waiting in line, where the person who arrived first is the first one to be served. In a queue, elements are added at one end, known as the rear, and removed from the other end, known as the front. The operations performed on a queue are:

1. Enqueue: Adds an element to the rear of the queue.
2. Dequeue: Removes the front element from the queue.
3. Peek: Returns the value of the front element without removing it.
4. IsEmpty: Checks if the queue is empty.

Queues are commonly used in scenarios where the order of processing is important, such as task scheduling, breadth-first search, and simulation of real-world scenarios. The most common implementation of a queue is using an array or a linked list.

In summary, the main difference between a stack and a queue lies in the order in which elements are added and removed. A stack follows the LIFO principle, while a queue follows the FIFO principle. Stacks are used when the last element added needs to be accessed first, while queues are used when the first element added needs to be accessed first.