Incoporate answer sheets into the repository

[Yanguangchen]

i don;t know the official sources, but having answer sheets to the practice problems is essential to practicing in the first place

there is no way to review mistakes and defeats the purpose of practicing if timely feedbacks are not provided

[tarrasque]

Hi @Yanguangchen
I see your point and understand that a neat collection of documents with the most up-to-date responses and feedback would be very helpful.

However it is not an improvement that we can handle here in GitHub directly due to too many changes to approve and merge.

I suggest you find volunteers on Slack, perhaps using the #repl channel to check and edit the contents, then once they are complete you can put them on GitHub.