added the solution of HQ9+ problem in codeforces

[gaurav23122001]

Hey there!, Thanks for submitting a PR to this repo Please complete the following checklist for your PR to be approved. Mark the items by adding an x.
Example: - [ ] Mark me as completed
To mark: - [x] Mark me as completed

• [x] My Pull Request adheres to the Contribution guidelines.
• [x] I have added readme.md and solution files in the appropriate folder
• [x] None of the folder and file names I have added contain any invalid characters, leading digits or trailing whitespaces
• [x] The solution I have given is my own and not plagiarized in any form.
• [x] My solution passes all the testcases.
• [x] I have properly indented and documented my solution using comments.

If any of the above is unmarked, please make the necessary changes and then mark them so that you're PR can be approved and merged.

[mergify[bot]]

Hey there, Your PR has been closed due to one or more of the following reasons:1) Your problem and/or solution file/folder are not named correctly. Please refer Contributing for guidelines. 2) Your file/folder name contains special characters or leading digits, please remove them. You may submit another Pull Request with the necessary changes made, Thanks