Create FourSumProblem.java

[mouss3abbb]

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized it.
• [x] All filenames are in PascalCase.
• [x] All functions and variable names follow Java naming conventions.
• [x] All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.

[BamaCharanChhandogi]

Hi, please write only one approach with good time complexity. You don't need to write all approaches. Also, remove the main method and add test cases

[mouss3abbb]

Feel free to check the last commits

[BamaCharanChhandogi]

@vil02 let's take this 1 PR for four sum problem. could you review this one?

[mouss3abbb]

@vil02 Thanks for your changes! Hopefully I completed all of them. Let me know if there is any issue

[siddhant2002]

Can I work under this issue?

[siriak]

@mouss3abbb are you working on it or @siddhant2002 can pick this up?

[mouss3abbb]

@mouss3abbb are you working on it or @siddhant2002 can pick this up?

I am working on it

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution!

[github-actions[bot]]

Please reopen this pull request once you have made the required changes. If you need help, feel free to ask in our Discord server or ping one of the maintainers here. Thank you for your contribution!