Implementing java code for Problem First Missing Positive

[10vulture1005]

What does this PR do?

Allowing users to input an array from the console and get the first missing positive integer.

Description

• Users can now run the program and input the array size and elements directly.
• The program prints the first missing positive integer as output.
• Retains the original logic for in-place swapping and O(n) time complexity.

Why is this valuable?

Previously, the method could only be tested programmatically. This addition allows interactive testing, making it easier for beginners to verify the solution with custom input.

Checklist

• Code compiles and runs correctly.
• Proper input/output prompts added.
• Preserves original algorithm functionality.

[github-actions]

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[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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