Lecture on Stacks and Queues

Introduction

This lecture is part of the "Complete Data Structures Algorithms plus Interview Preparation Bootcamp".
Focus is on Stacks and Queues.
Importance of understanding data structures, their use cases, optimization, and appropriate use.

Definition: A stack is a linear data structure that follows the Last In First Out (LIFO) principle.
Use Case: Example of stack usage in recursion, where function calls are pushed onto the stack and popped off when executed.
Real World Analogy: Plates stacked at a buffet; the last plate added is the first one to be taken.
Operations:
- Push: Add an item to the top of the stack.
- Pop: Remove the top item from the stack.
Implementation Details: Internal implementation often involves arrays.

Definition: A queue is a linear data structure that follows the First In First Out (FIFO) principle.
Real World Analogy: People standing in line at a restaurant; the first person in line is the first to be served.
Operations:
- Enqueue: Add an item to the end of the queue.
- Dequeue: Remove an item from the front of the queue.
Implementation Details: Often implemented using linked lists.

Example Code for Stack: Demonstrates how to use the stack in Java using the stack class, covering push and pop operations.
Example Code for Queue: Uses a linked list to implement a queue, demonstrating enqueue and dequeue operations.

Deque (Double-Ended Queue): Allows insertion and removal of elements from both ends.
ArrayDeque: Provides a resizable array implementation of the deque interface. Faster than stacks and queues for most operations.

Custom Stack: Implement a stack using arrays with dynamic resizing.
Custom Queue: Implement a queue using arrays and discuss complexity issues.
Circular Queue: Implement a circular queue to improve efficiency, allowing wrap-around in the array.

Stacks and queues generally offer O(1) time complexity for push and pop operations.
Removal in a simple queue can be O(n), but using a circular queue can improve this to O(1).

Stacks and queues are useful for storing intermediate results, reversing data, and implementing recursive algorithms iteratively.
BFS and DFS algorithms extensively use stacks and queues.
Application examples include managing function calls, scheduling processes, and real-time transaction processing.

Stacks and queues are foundational data structures with wide applications in computer science.
Proficiency in these concepts is crucial for solving complex problems efficiently.