The Terms and Conditions states:
Link should direct the judges to a repository containing your code, which can be hosted on a Version Control System, such as Github or Bitbucket. In that repository, you should include a README.txt or README.md file in the root directory. This file should contain clear instructions on how to run your code for us to be able to test out the solution.
So, if you’re running a public repository on Github, Bitbucket, or similar version control system, you can simply give us the link. But, if you want to keep your repo private, you have two options:
1) You can host your code in a private google drive folder and submit a share link.
2) In your Version Control System, you can give read access to the following email address: firstname.lastname@example.org