I created a video that talks about how to efficiently and easily compute the next smaller element, second next smaller element and so on, using a set instead of stack. It also talks about a non trivial contribution technique that recently appeared as part of problem E: Range Minimum Sum from Codeforces Round 958.

Here is the video link https://youtu.be/MRlaULKT9V4?si=PfpyqPIJns0OMRqb

I also curated some practice problems and created easy version of problem E. You can find the contest here https://mirror.codeforces.com/group/7Dn3ObOpau/contest/537569

The problems are untested, if you see any issues, do let me know.