Questions: Given binary tree, convert tree to the circular doubly linkedlist.

I have done this question two week back as it was one of the FB tagged questions. Still I was not able to write the code for it. It really feel frustating to me.
I have done 208 LC (64 Easy, 124 medium, 20 hard). I am not sure what is wrong with me. I just keep forgetting patterns. Even if I know the solution I just forget how to write the code quickly.
Any suggestion how can I do better.
Not able to write the code quickly, I think this is my problem. Has anyone faced similar problem.