Stack

3.1 INTRODUCTION

In this section, the concept of data structures is introduced as a fundamental mechanism for storing, organizing, and accessing data efficiently. Data structures group multiple data elements in a particular way to enable faster accessibility and efficient storage of data. For example, strings, lists, sets, and tuples in Python are sequence data types that can represent a collection of elements either of the same type or different types. A data structure defines a mechanism to store, organize, and access data along with operations (processing) that can be efficiently performed on the data. For instance, a string is a data structure containing a sequence of characters, while a list is a sequence data structure where each element may be of different types. Various operations such as reversal, slicing, and counting can be performed on these data structures. Other important data structures in computer science include arrays, linked lists, binary trees, heaps, graphs, and sparse matrices. A data structure in which elements are organized in a sequence is called a linear data structure. Stack and queue are two other popular linear data structures used in programming. Although not directly available as built-in types in Python, it is important to learn these concepts as they are extensively used in many programming languages. This chapter focuses on the stack data structure, its implementation in Python, and its applications.

• Data structures group multiple data elements for efficient storage and access.
• Strings, lists, sets, and tuples are sequence data types in Python.
• A data structure organizes data to perform operations efficiently.
• Linear data structures arrange elements in a sequence.
• Stack and queue are important linear data structures used in programming.
• Stack is not a built-in Python data type but can be implemented using lists.
• 📌 Data Structure: A mechanism to store, organize, and access data efficiently.
• 📌 Linear Data Structure: A data structure where elements are arranged sequentially.

3.2 STACK

This section introduces the stack data structure by drawing analogies with everyday objects such as piles of books or plates. A stack is a linear arrangement where elements are added and removed from only one end, called the top. For example, when placing a book or plate on a pile, it is always added on the top, and similarly, removal is done from the top. This is because accessing elements from the middle or bottom of a large pile is inconvenient. This arrangement follows the Last-In-First-Out (LIFO) principle, meaning the element inserted last is the first to be removed. The stack is a linear data structure where insertion and deletion happen at the same end, the top of the stack. This principle is fundamental to understanding stack operations and their applications in programming and real life.

• Stack is a linear data structure with insertion and deletion at one end only (top).
• Follows Last-In-First-Out (LIFO) principle.
• Elements are added (PUSH) and removed (POP) from the top of the stack.
• Analogous to piles of books or plates where only the top element is accessible.
• Stack is used to organize elements in a sequence with restricted access.
• Efficient for scenarios where recent data needs to be accessed first.
• 📌 Stack: A linear data structure that follows LIFO principle.
• 📌 Top: The end of the stack where elements are inserted or removed.
• 📌 LIFO (Last-In-First-Out): The last element inserted is the first to be removed.