Stack

A Stack is one-ended linear data structure which models a real world stack by having two primary operations, namely push and pop.

Introduction

You can think of the Stack as a container, in which we can add items and remove them. Only the top of this container is open, so the item we put in first will be taken out last, and the items we put in last will be taken out first. This is called the last in first out (LIFO) ordering.

Stacks and queues can be effectively implemented using either arrays or linked lists. The key issue is whether an upper bound on the size of the container is known in advance, thus permitting the use of a statically-allocated array.

Unlike an array, a stack does not offer constant time access to the i-th item. However, it does allow constant-time adds and removes, ad it doesn't require shifting elements around.

When and Where is a Stack used?

Undo mechanism in the editor.
Compiler syntax checking for matching brackets and braces
To model a pile of books or plates
Behind the scenes to support recursion by keeping track of previous function calls.
Depth-First Search (DFS). To implement a recursive algorithm iteratively.
In certain recursive algorithms. Sometimes you need to push temporary data onto a stack as you recurse, but then remove them as you backtrack (for example, because the recursive check failed)
A stack can be used to implement a recursive algorithm iteratively.
To store a partially completed task, e.g., when you are exploring two different paths on a Graph from a point while calculating the smallest path to the target.