Is a Stack a Data Structure?

A **data structure** is a way of organizing and storing data in a computer’s memory. It provides an efficient way to access and manipulate the stored data.

One such popular data structure is **a stack**. But is a stack really considered a data structure? Let’s find out.

## What is a Stack?

A stack is an abstract data type that follows the __Last-In-First-Out (LIFO)__ principle. It operates on elements in a sequential manner where the last element added to the stack is the first one to be removed. Think of it as stacking plates – you can only remove the topmost plate, which was placed last.

A stack offers two fundamental operations:

**Push:**Adds an element to the top of the stack.**Pop:**Removes and returns the topmost element from the stack.

## The Implementation Perspective

From an implementation perspective, a stack can be built using various underlying data structures, such as arrays or linked lists. This means that while a stack itself may not be considered a distinct data structure, it relies on other existing data structures for its functionality.

### An Array-Based Implementation

In an array-based implementation, we use an array to represent the stack. The top of the stack is denoted by an index pointing to the last inserted element.

When pushing an element, we increment this index and insert the new element at that position. Similarly, when popping an element, we retrieve it from that position and decrement the index.

```
class Stack {
constructor() {
this.stack = [];
this.top = -1;
}
push(element) {
this.top++;
this.stack[this.top] = element;
}
pop() {
if (this.isEmpty()) {
return undefined;
}
const poppedElement = this.top];
this.stack.splice(this.top, 1);
this.top--;
return poppedElement;
}
isEmpty() {
return this.top === -1;
}
}
```

### A Linked List-Based Implementation

In a linked list-based implementation, we use a singly linked list to represent the stack. Each element in the stack is represented as a node, which holds the actual data and a reference to the next node in the list.

```
class Node {
constructor(data) {
this.data = data;
this.next = null;
}
}
class Stack {
constructor() {
this.head = null;
}
push(element) {
const newNode = new Node(element);
if (this.isEmpty()) {
this.head = newNode;
return;
}
newNode.next = this.head;
this.head = newNode;
}
const poppedElement = this.head.data;
this.head = this.next;
return poppedElement;
}
isEmpty() {
return !this.head;
}
}
```

## Conclusion

A stack is indeed considered a data structure, although it relies on other underlying data structures for its implementation. It provides an intuitive way to store and retrieve elements in a specific order, making it useful in various computer science applications.

By understanding the concept of stacks and their implementations, you can utilize them effectively for solving problems that require LIFO behavior.