Introduction to Stack

Grokking Data Structures & Algorithms for Coding Interviews

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Introduction to Stack

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A stack is a linear data structure that follows the Last-In, First-Out (LIFO) principle. This means that the last element added to the stack is the first one to be removed.

Understanding Stacks with a Real-Life Analogy

Imagine a stack of books on a table. When you add a new book, you place it on top of the stack. When you want to remove a book, you take the topmost book first. The last book you added is the first one you take out—this is how a stack works.

Stack of books

The LIFO Principle

Stacks operate based on the Last-In, First-Out (LIFO) principle, which means:

The most recently added item is removed first.
The first item added remains at the bottom until everything above it is removed.

For example, consider a stack containing numbers:

Push(50) → Adds 50 to the top
Stack after push: [10, 20, 30, 40, 50]
Pop() → Removes 50 (topmost element)
Stack after pop: [10, 20, 30, 40]

This predictable behavior makes stacks efficient for handling ordered data.

Basic Stack Operations

A stack provides four fundamental operations:

Push → Adds an element to the top of the stack.
Pop → Removes the topmost element from the stack.
Peek (or Top) → Returns the topmost element without removing it.
IsEmpty → Checks if the stack is empty.
IsFull → Checks if the stack is full.

Each of these operations follows the LIFO order, ensuring efficient data management.

In the next lesson, we will explore stack operations in detail, including their time complexities and practical implementations.

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