An ad-hoc problem, I enjoyed the editorial comments because people came up with more than 10 ways to solve the problem and my method was one of the most beautiful.

cp concepts are very limited always try to think of topics for a sec and you'll get it right by your logic (piggybacked by your intuition)

Simple mix of binary search + DP, DP logic is also cool and simple

Simple reverse thinking for exhaustive search using basic PnC

How to use tin and tout for a generic tree and check if u is ancestor of v or not.

Simple use of stack for maintaining order (similar to sliding window maximum)

Double binary search n(logn)^2

Simple Dijkstra, but from the n-1 to 0 with simple modified logic.

Also, sometimes in modified dijkstra when there could be multiple redundant entries, using a set will save you from TLE.

Pre computation OR dp is necessary to not get TLE, harmonic complexity is cool. BS on range is also cool.

Will share more if remember any. I have few favs higher rated than 1800