Lecture Notes: Queue Data Structure

Introduction

• Presenter: Tanmay from Simple Snippets
• Topic: Queue Data Structure (part of Data Structures and Algorithms series)
• Format: Two-part tutorial
  • Part 1: Overview of Queue Data Structure
  • Part 2: Implementation in C++

Overview of Queue Data Structure

Definition and Characteristics

• Linear Data Structure: Operates in a sequential manner
• FIFO/LILO Principle: First In First Out or Last In Last Out
  • Opposite of Stack's FILO/LIFO principle
• Real-world Analogy: Similar to a queue of cars or people waiting in line (first come, first served)
• Abstract Data Type: May have a bounded (predefined) capacity

Operations

• Standard Operations:
  • Enqueue (add element)
  • Dequeue (remove element)
  • IsFull
  • IsEmpty
  • Count (number of elements)
• Additional Operations: Peak and Change (less relevant)

Memory Representation

• Diagrammatic View: Visual representation using a matrix format considering it as RAM
  • Memory addresses like #1000, #1001, etc.
• Queue of Size 4: Visualized with start (front/head) and end (rear/back)

Key Points

• Enqueue: Adding elements at the rear
• Dequeue: Removing elements from the front
• Initialization: Rear and front pointers set to -1 initially

Detailed Operations and Algorithms

Initialization

• Use arrays to implement Queue
• Variables:
  • int arr[4] (array size of 4)
  • rear and front variables to track positions

Enqueue Operation

• Check if the queue is full
• Use rear++ to track position for adding elements
• Update front and rear pointers

Dequeue Operation

• Check if the queue is empty
• Remove from front, update front (front++)
• Special case when only one element is left

IsFull and IsEmpty

• IsFull: Checks if rear equals size of arr - 1
• IsEmpty: Checks if both front and rear are -1

Count

• Count Calculation: Difference between rear and front plus one

Limitations

• Unused Space: Linear queue implementation can lead to unused space; requires circular queues for optimization

Applications of Queue

• CPU Scheduling: Processes execution order
• Disk Scheduling
• Handling of Interrupts: First come, first serve basis
• Real-life Examples: Call center systems, asynchronous data transfer

Conclusion

• Understanding of what a Queue data structure is
• Detailed look at standard operations and their algorithms
• Preparation for practical implementation in C++ in the next tutorial

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