Add Counting Sort implementation in Java

[Pasan11504]

Add Counting Sort Implementation in Java

Problem: Counting Sort Algorithm

This PR adds a comprehensive Counting Sort implementation to Java/sorting/.

Description

Counting Sort is a non-comparison based sorting algorithm that sorts elements by counting the number of occurrences of each unique element. It's particularly efficient for sorting integers with a small range.

Implementation Details

Algorithm Steps:

1. Find the range of input data (max and min values)
2. Create a count array to store frequency of each element
3. Modify count array by adding previous counts (cumulative count)
4. Build output array by placing elements at their correct positions
5. Copy output array back to original array

Features:

• ✅ Two implementations:
  • countingSort() - for non-negative integers
  • countingSortWithNegatives() - handles negative numbers using offset
• ✅ Stable sorting - maintains relative order of equal elements
• ✅ Comprehensive comments - every step explained clearly
• ✅ Problem name mentioned in file header
• ✅ 10 test cases - covering all scenarios and edge cases
• ✅ Error handling - validates input for negative numbers

Complexity Analysis

• Time Complexity: O(n + k) where n = number of elements, k = range of input
• Space Complexity: O(n + k)

Why This is Valuable

• Missing algorithm: Java/sorting/ only had 6 sorting algorithms, Python had 16 including Counting Sort
• Fundamental algorithm: Important non-comparison based sorting technique
• Educational value: Well-documented with clear explanations
• Production ready: Includes error handling and comprehensive testing

Test Results

All 10 test cases passed:
✅ Standard array sorting
✅ Already sorted array
✅ Reverse sorted array
✅ Array with many duplicates
✅ Single element array
✅ All same elements
✅ Large numbers
✅ Array with zeros
✅ Negative numbers (alternative method)
✅ Error handling for invalid input

Guidelines Followed

• Problem name clearly mentioned in comments
• Code well-commented
• Proper file naming: CountingSort.java
• Correct directory: Java/sorting/
• No duplicate (verified existing files)
• Compiled and tested successfully

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Ready for Hacktoberfest 2025! 🎃

[github-actions]

🎉 Welcome to Hacktoberfest 2025, @Pasan11504! 🎃

Thank you for your first contribution to our DSA repository! Here's what happens next:

🔍 Automatic Checks

• ✅ Code Validation: Passed
• 🧪 Compilation Tests: Passed

📋 Next Steps

🎯 Great job! Your code compiled successfully. Maintainers @admirerr and @kartikey2991 will review your PR soon.

🎁 What You Get

• 🏆 Hacktoberfest Credit: This PR counts toward your 6 PR goal for exclusive T-shirt + Tree!
• 🌟 Hall of Fame: You'll be featured in our contributors list
• 📚 Learning: Code review feedback from experienced developers

💡 Tips for Success

• Follow our Contributing Guidelines
• Add comments explaining your algorithm
• Include time/space complexity analysis
• Test your code before submitting

Welcome to the community! 🚀

[github-actions]

🤖 Automated PR Status

🔍 Code Validation

✅ Passed - File naming and structure look good!

🧪 Compilation Tests

✅ Passed - All code compiles successfully!

📋 Overall Status

🎉 Ready for Review - Your PR has passed all automated checks!
👥 Maintainers have been notified for review.

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[admirerr]

Approved