**How Stack Is Implemented in Data Structure?**

A stack is a fundamental data structure that follows the Last-In-First-Out (LIFO) principle. It is commonly used in programming and computer science to efficiently manage data. In this article, we will delve into the implementation of a stack in a data structure, exploring its operations, key concepts, and how it can be implemented using various programming languages.

## The Basics of a Stack

Before diving into the implementation details, let’s quickly recap what a stack is and how it works.

**Definition:**A stack is an abstract data type that represents a collection of elements with two main operations:__push__and__pop__. The push operation adds an element to the top of the stack, while the pop operation removes the topmost element.**Last-In-First-Out (LIFO):**As mentioned earlier, stacks follow the LIFO principle. This means that the last element added to the stack will be the first one to be removed.

## Implementing a Stack

In order to implement a stack, we need to decide on an underlying data structure. There are multiple ways to achieve this; two popular approaches are using arrays or linked lists.

### Array-based Implementation

An array-based implementation of a stack utilizes an array to store the elements. Let’s explore how this can be achieved:

- Create an empty array with a fixed size or use dynamic resizing techniques if available in your programming language.
- Maintain a variable called
*top*, initially set to -1, which represents the index of the topmost element in the stack. **Push operation:**To push an element onto the stack, increment the*top*variable and store the new element at that index in the array.**Pop operation:**To pop an element from the stack, retrieve the element at the index specified by*top*, decrement*top*, and return that element.

This implementation has a constant time complexity of O(1) for both push and pop operations, making it efficient for most use cases.

### Linked List-based Implementation

A linked list-based implementation of a stack utilizes a linked list data structure to store elements. Here’s how it works:

- Create an empty linked list with a head node representing the top of the stack.
**Push operation:**To push an element onto the stack, create a new node containing that element and insert it at the beginning of the linked list, making it the new head node.**Pop operation:**To pop an element from the stack, remove and return the current head node of the linked list. Update the head pointer to point to its next node.

This implementation also has a time complexity of O(1) for both push and pop operations. However, it may require more memory compared to an array-based implementation due to additional pointers in each node.

## Conclusion

In this article, we explored how stacks are implemented in data structures using arrays or linked lists. We discussed their basic operations and highlighted their efficiency. The choice between array-based or linked list-based implementation depends on the specific requirements of your application.

Remember to consider the trade-offs between time complexity, memory usage, and ease of implementation when choosing the appropriate stack implementation for your project. Happy coding!