Stack

Stack:

                Stack is a linear data structure that follows a particular order in which the operations are performed.

Push: Adds an item in the stack. If the stack is full, then it is said to be an Overflow condition.

Pop: Removes an item from the stack. The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.

Peek or Top: Returns the top element of the stack.

isEmpty: Returns true if the stack is empty, else false.

How to understand a stack practically? 

There are many real-life examples of a stack. Consider the simple example of plates stacked over one another in a canteen. The plate which is at the top is the first one to be removed, i.e. the plate which has been placed at the bottommost position remains in the stack for the longest period of time. So, it can be simply seen to follow the LIFO/FILO order.

Time Complexities of operations on stack:

push(), pop(), isEmpty() and peek() all take O(1) time. We do not run any loop in any of these operations.

 

Applications of stack:

Balancing of symbols

Infix to Postfix /Prefix conversion

Redo-undo features at many places like editors, photoshop.

Forward and backward feature in web browsers

Used in many algorithms like Tower of Hanoi, tree traversals, stock span problem, histogram problem.

Backtracking is one of the algorithm designing techniques. Some examples of backtracking are the Knight-Tour problem, N-Queen problem, find your way through a maze, and game-like chess or checkers in all these problems we dive into someway if that way is not efficient we come back to the previous state and go into some another path. To get back from a current state we need to store the previous state for that purpose we need a stack.

In Graph Algorithms like Topological Sorting and Strongly Connected Components

In Memory management, any modern computer uses a stack as the primary management for a running purpose. Each program that is running in a computer system has its own memory allocations

String reversal is also another application of stack. Here one by one each character gets inserted into the stack. So the first character of the string is on the bottom of the stack and the last element of a string is on the top of the stack. After Performing the pop operations on the stack we get a string in reverse order.

Implementation: 

There are two ways to implement a stack: 

Using array

Using linked list