What is a Stack?

Stack follows the LIFO (Last-In-First-Out) principle. The last element added is the first one to come out.

Stack Operations

• Push: Add an element to the top
• Pop: Remove the top element
• Peek/Top: View the top-most element

Visualisation:

Example Flow

• stack.push(1) → [1]
• stack.push(3) → [1, 3]
• stack.pop() → returns 3 → [1]
• stack.peek() → returns 1

Examples

• Stacks of Books
• Undo/Redo feature
• Recursion (Function Call Stack)
• Browsing History

What is a Queue?

Queue follows the FIFO (First-In-First-Out) principle. The first element added is the first to be removed.

Queue Operations

• Enqueue: Add an element to the end
• Dequeue: Remove element from the front
• Peek/Front: View the front-most element

Visualisation:

Examples

• Ticket Counter
• OS Task Scheduling
• Printers
• Queues (in general)

Why Use Stack and Queue❓

• Organize data logically (based on problem’s need).
• Order of Operations Matter
• Optimize time & memory for specific scenarios

Use Cases

• Recursion (stack)
• Level Order Traversal (queue)
• BFS (queue)
• DFS (stack)

Language Implementation

JavaScript

let stack = [];
stack.push(10);
stack.push(7);
stack.pop();    // returns 7
stack.pop();    // returns 10
    

Java

Stack stack = new Stack<>();
stack.push(10);
stack.pop();
stack.peek();
    

C++

#include 
std::stack s;
s.push(10);
s.pop();
s.top();
    

Python

stack = []
stack.append(10)
stack.pop()
top = stack[-1]  # peek
    

Note:Find out more about stacks in your preferred programming language.

Stack vs Queue

comparison with other Data-Structures