Added solution for Maximum Sum of Non-Adjacent Elements problem

[Adityakumar37]

✅ Checklist

Please ensure your PR meets these requirements:

Code Quality

• [ ✅] Solution follows the required template format
• [✅ ] Code is clean and well-commented
• Variable names are descriptive
• [ ✅] Proper error handling for edge cases

Testing

• [ ✅] Solution passes all CSES test cases
• [ ✅] Tested with custom edge cases
• [ ✅] Handles large input constraints efficiently
• [ ✅] No runtime errors or timeouts

Documentation

• [ ]✅ Added solution to appropriate category folder
• [ ✅] File name follows naming convention (snake_case)
• [ ✅] Added brief comment explaining the approach
• [ ✅] Updated any relevant documentation if needed

Style Guide

• [ ✅] Uses required headers (#include <bits/stdc++.h>)
• Includes fast I/O optimization
• Uses appropriate data types (long long for large numbers)
• Follows competitive programming best practices

🏷️ Type of Change

• 🐛 Bug fix (fixes an existing solution)
• ✨ New problem solution
• 📚 Documentation improvement
• 🔧 Code optimization/refactoring
• [ ✅] 🎃 Hacktoberfest contribution

🧪 Testing Details

Describe how you tested your solution:

Test Cases Used:

Input: 
Expected Output: 
Actual Output: 

📸 Screenshots (if applicable)

Add screenshots of successful submissions or any relevant visuals.

📎 Additional Notes

Any additional information, considerations, or context for reviewers:

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For Maintainers:

• Code review completed
• Solution verified on CSES judge
• Documentation updated if needed
• Labels applied appropriately

[Adityakumar37]

Input: [3, 2, 7, 10]

Expected Output: 13

Actual Output: 13