feat: Add comprehensive Queue data structure

[Brijesh03032001]

📚 Add Comprehensive Queue Data Structure Implementation

🎃 Hacktoberfest 2025 Contribution - Queue Data Structure

🚀 Summary

This PR introduces a comprehensive Queue data structure implementation in R, contributing valuable educational content to TheAlgorithms/R repository with focus on pure data structure concepts.

📁 What's Added

• /data_structures/Queue/ - New organized folder structure
• queue_operations.r - Complete Queue implementation (290+ lines)
• Updated DIRECTORY.md - Proper documentation linking

✨ Key Features

🔧 Queue Operations (queue_operations.r)

• Core Operations: enqueue(), dequeue(), front(), rear(), size(), isEmpty()
• Advanced Features: Bounded queues, overflow/underflow protection
• Bonus Implementation: Priority Queue with custom priorities
• Error Handling: Comprehensive edge case management
• Interactive Demo: Step-by-step operation demonstrations
• Educational Examples: Clear FIFO principle demonstrations

🎯 Priority Queue Implementation

• Custom Priority Support: Elements ordered by priority values
• Flexible Comparison: Supports both numeric and custom comparisons
• Real-world Applications: Task scheduling, event management
• Complete Interface: All standard queue operations with priority handling

🧠 Educational Impact

• Beginner-Friendly: Clear documentation and examples
• Data Structure Focus: Pure implementation without problem-solving complexity
• Algorithm Understanding: Demonstrates FIFO principles clearly
• Best Practices: Proper R coding standards and error handling
• Comprehensive Coverage: Both basic Queue and Priority Queue variants

🔍 Code Quality

• ✅ Lint-Free: No R linting warnings
• ✅ Tested: All functions verified with example outputs
• ✅ Documented: Comprehensive comments and explanations
• ✅ Modular: Clean separation of concerns
• ✅ Standards: Follows repository naming conventions

🎮 Demo Output

# Queue Operations Demo
Queue initialized with max size: unlimited
Enqueued: Task A | Size: 1
Enqueued: Task B | Size: 2
Enqueued: Task C | Size: 3
Queue: [ Task A <- Task B <- Task C ] (front <- rear)
Dequeued: Task A | Size: 2
Front element: Task B
Rear element: Task C

# Priority Queue Demo
Priority Queue initialized
Adding: (Emergency, priority: 1)
Adding: (Normal, priority: 5)
Adding: (Urgent, priority: 2)
Dequeue order: Emergency → Urgent → Normal

🏗️ Architecture

• Reference Classes: Proper OOP implementation in R
• Memory Efficient: Smart memory management for large queues
• Extensible: Easy to add more Queue variants
• Clean Interface: Intuitive method names and consistent behavior

🎓 Learning Outcomes

Students and developers will learn:

• Queue ADT: Complete understanding of FIFO data structure
• Priority Queues: Advanced queue concepts with ordering
• Data Structure Design: Proper implementation patterns in R
• R Programming: Advanced R concepts and best practices
• Algorithm Complexity: Understanding O(1) operations

🌟 Hacktoberfest Spirit

This contribution embodies Hacktoberfest values:

• Quality: Well-tested, documented, and educational code
• Community: Helps R developers learn data structures
• Growth: Expands TheAlgorithms repository with valuable content
• Accessibility: Clear examples for learners at all levels
• Pure Focus: Educational data structure without problem-solving complexity

🚦 Testing Instructions

# Test Queue operations
Rscript data_structures/Queue/queue_operations.r

📊 Complexity Analysis

• Enqueue: O(1) - Adding element to rear
• Dequeue: O(1) - Removing element from front
• Front/Rear: O(1) - Accessing elements
• Size/isEmpty: O(1) - Status checking
• Priority Queue: O(n) for insertion (maintains order)

🎯 Applications Covered

• CPU Scheduling: Process management queues
• Print Queues: Document processing order
• Buffer Management: Data stream handling
• Level Order Traversal: Tree algorithm foundation
• Task Management: Priority-based job scheduling

🔄 Queue Variants Included

1. Basic Queue: Standard FIFO implementation
2. Bounded Queue: Size-limited with overflow protection
3. Priority Queue: Element ordering by priority
4. Interactive Examples: Step-by-step demonstrations

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Ready for review! 🚀 This contribution adds significant educational value focusing purely on Queue data structure concepts. Perfect for Hacktoberfest 2025! 🎃

Related: Hacktoberfest 2025, Data Structures, Queue, FIFO, Priority Queue

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📋 PR Checklist

• Code follows repository standards
• Comprehensive documentation included
• All functions tested with examples
• DIRECTORY.md updated appropriately
• Focus on educational data structure implementation
• No external dependencies required
• Proper error handling implemented

[siriak]

Looks good, thanks!