I'm preparing the upcoming ICPC. Can anyone tell me some tricks on Tree/Graph/Sequence in ICPC?

After being orange, I found a new option, propose a contest/problems. Can anyone tell me how to do that if I want to propose a contest/problems? Thanks a lot!

In recent contest, I couldn't enter codeforces because of Human machine verification for over 15 minutes after the contest started. This gave me a very bad experience and I have to vp at another time. What can I do? I don't want to read the problems 15 minutes or more later than others, especially in next div1+2.

problem D from CodeTON Round 8, my code get MLE: https://codeforces.me/contest/1942/submission/254227380, but why? I solve it in O(nklogn), and memory for O(nk), and MLE on test 5.

Anyone has some advice for practice? Sometimes I can solve difficulty up to 2400 but sometimes can't.

upd: Can anyone suggest some difficult and important algorithm that a GM needs to learn?