Introduction to Stack — Data Structures & Algorithms

Introduction

In the realm of computer science, data structures play a pivotal role in organizing and managing data efficiently. One such fundamental and versatile data structure is the “Stack.”

A stack is a collection of elements that follows the Last-In, First-Out (LIFO) discipline, resembling a physical stack of items where the last item added is the first to be removed.

Some real-world examples of stack

Multilevel Stack Car Parking in Shopping Malls

Envision a multilevel parking structure commonly found in shopping malls. As cars enter and are parked on different levels, the last car parked on a specific level becomes the first to exit. This scenario perfectly illustrates the Last-In, First-Out (LIFO) nature of a stack, where the latest addition is the first to be retrieved.

Stack of cars in a multilevel car parking

Can of Pringles

Consider a cylindrical can of Pringles chips. When you stack new chips into the can, the existing ones are pushed down. When you reach for a chip, you grab the last one added, creating a stack-like behavior.

Stack of chips inside a can of Pringles

Stacked Trays in Cafeterias

Visualize the trays in a cafeteria stacked on top of each other. As people take trays from the top, the last tray added is the first to be used. This arrangement follows the LIFO principle, resembling a stack data structure.

Stack of trays in a cafeteria

Stack ADT

In the context of a stack, ADT stands for “Abstract Data Type.”

Abstract Data Type (ADT) is an abstraction that defines a set of operations on a data type, hiding the implementation details.

Stack ADT simplifies the way we think about stacks in programming. It’s like a blueprint that outlines how stacks should work without getting into complicated details. It comprises of three crucial elements: Data, Representation of Data, and Operations on Data.

Data

1. Space for Storing Elements: Represents the memory or storage needed to hold stack elements.
2. Top Pointer: Indicates the current topmost element in the stack.

Representation

Representation of Stack

Operations

1. Push(): Adds an element to the top of the stack.
2. Pop(): Removes and returns the element from the top of the stack.
3. Peek(): Returns the element at the top of the stack without removing it.
4. StackTop(): Returns the topmost element of the stack.
5. isEmpty(): Checks if the stack is empty.
6. isFull(): Checks if the stack is full (applies mainly to a fixed-size array implementation).

Implementation of Stack

1. Using Array: Involves a fixed-size array to store elements, with the top pointer tracking the current position in the array.
2. Using Linked List: Utilizes a linked list structure, where each node holds an element, and the top pointer points to the first node.

Conclusion

Understanding the stack’s conceptualization and its abstract representation sets the stage for exploring its applications, from handling function calls in recursion to parsing expressions in compilers. Subsequent articles will delve into detailed insights into stack implementations and real-world use cases. Happy stacking! 👩‍💻