I am studying graphs from galen_colin yt channel and came across these links where he said to do them as practice problems, but when clicking it shows: You are not allowed to view the contest. Ex: https://mirror.codeforces.com/gym/383769/problem/B, https://mirror.codeforces.com/gym/383769/problem/D and more. How do I access these questions? Thanks a lot in advance.

I started learning C++ STL and learned topics like Vectors, Maps(2), and Sets(all 3), now I would like to start solving questions involving these concepts. So can anyone guide me on how to find questions related to these 3 on codeforces? Please don't dislike if this is a repeated question or if I said something wrong.

Thanks in advance!

I'm a beginner coder, I know for the first 4-5 contests my rating will only increase even if my code doesn't get accepted. My question is, after the initial 5 contests, how to know how many questions to solve in a contest considering the user Rating, the number of Previous contests he has given, and ideally under which time he should submit the code to NOT DECREASE THE RATING?

I'm asking this because one of my friends even after solving 1 question of division 2, his rating decreased twice. So, I can avoid this in the future. It would be super helpful if someone give some more insight into this, thank you.