What are some Div2 C/D/E problems that can be solved by convex hull / line sweep/ dot or cross product? Also are there any other geometry algorithms important for codeforces problems?

The question :- Find the size of the largest complete subtree in a binary tree.
A complete binary tree is a tree with all levels filled except the last which is left filled.
I tried a postorder type approach but there were just too many cases to handle. I could not find the answer on google so I decided to ask it here

Hello everyone,
I have been solving competitive programming problems for about a year (on other online judges). I have learnt various standard algorithms like bfs/dfs, bitmask technique etc and I feel I have made reasonable progress in those topics and can solve easy — medium problems of those topics. However the same is not true for dynamic programming.

I must have solved over a hundred dynamic programming problems, yet when I see a new one I have no idea how to solve it. I feel as if each problem is completely different from the other. Also I cannot see any pattern in their solutions like I see for problems related to other standard techniques. I would appreciate it if anyone could guide my on how to go about solving dp problems, a proper methodical approach . Please do say something like "practice makes perfect" because I have solved a lot of problems yet not made any progress.

Im hoping to get lots of responses cause I know there are many dp experts out there.

Thank You