Add comprehensive Stack data structure implementation

[Brijesh03032001]

📚 Add Comprehensive Stack Data Structure Implementation

🎃 Hacktoberfest 2025 Contribution - Stack Data Structure

🚀 Summary

This PR introduces a comprehensive Stack 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/Stack/ - New organized folder structure
• stack_operations.r - Complete Stack implementation (400+ lines)
• Updated DIRECTORY.md - Proper documentation linking

✨ Key Features

🔧 Stack Operations (stack_operations.r)

• Core Operations: push(), pop(), peek(), top(), size(), isEmpty()
• Advanced Features: Bounded stacks, overflow/underflow protection
• Expression Evaluator: Infix to postfix conversion with operator precedence
• Balanced Parentheses Checker: Supports multiple bracket types (), [], {}
• Function Call Stack Simulator: Demonstrates function call mechanics
• Error Handling: Comprehensive edge case management
• Interactive Demo: Step-by-step operation demonstrations
• Educational Examples: Clear LIFO principle demonstrations

🎯 Advanced Stack Features

• Expression Processing: Mathematical expression evaluation and conversion
• Syntax Validation: Parentheses and bracket matching
• Call Stack Simulation: Understanding function call mechanics
• Memory Management: Proper stack frame handling
• Multiple Data Types: Support for various element types

🧠 Educational Impact

• Beginner-Friendly: Clear documentation and examples
• Data Structure Focus: Pure implementation without problem-solving complexity
• Algorithm Understanding: Demonstrates LIFO principles clearly
• Best Practices: Proper R coding standards and error handling
• Comprehensive Coverage: Multiple Stack use cases and applications

🔍 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

# Stack Operations Demo
Stack initialized with max size: unlimited
Pushed: A | Size: 1
Pushed: B | Size: 2
Pushed: C | Size: 3
Stack: [ A | B | C ] (bottom → top)
Popped: C | Size: 2
Top element: B

# Expression Evaluation Demo
Infix: 2 + 3 * 4
Postfix: 2 3 4 * +
Result: 14

# Parentheses Checking Demo
Input: "({[()]})"
Result: Balanced ✓
Input: "({[()]}]"
Result: Not Balanced ✗

🏗️ Architecture

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

🎓 Learning Outcomes

Students and developers will learn:

• Stack ADT: Complete understanding of LIFO data structure
• Expression Processing: Mathematical expression handling
• Syntax Parsing: Bracket and parentheses validation
• 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 Stack operations
Rscript data_structures/Stack/stack_operations.r

📊 Complexity Analysis

• Push: O(1) - Adding element to top
• Pop: O(1) - Removing element from top
• Peek/Top: O(1) - Accessing top element
• Size/isEmpty: O(1) - Status checking
• Expression Evaluation: O(n) - Linear processing
• Parentheses Checking: O(n) - Single pass validation

🎯 Applications Covered

• Function Calls: Call stack management and recursion
• Expression Evaluation: Mathematical expression processing
• Syntax Parsing: Bracket matching and validation
• Undo Operations: Command history management
• Browser History: Navigation stack implementation
• Memory Management: Stack frame allocation

🔄 Stack Features Included

1. Basic Stack: Standard LIFO implementation
2. Bounded Stack: Size-limited with overflow protection
3. Expression Evaluator: Infix to postfix conversion
4. Parentheses Checker: Multi-bracket validation
5. Call Stack Simulator: Function call demonstration
6. Interactive Examples: Step-by-step demonstrations

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

Related: Hacktoberfest 2025, Data Structures, Stack, LIFO, Expression Evaluation

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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!