I made a video editorial discussing Edu 160D — Array Collapse . The video talks about how to use monotonic stacks to perform DP transitions faster.

Youtube Link

I also created some basic problems to help you practice the stuff covered in the video. You can access the group using this link https://codeforces.com/group/7Dn3ObOpau In the contests section, you'll see a contest by the name Monotonic Stack + DP. If you want me to add even more basic problems, like finding the previous smaller element or next greater element, please let me know. The problems are untested, so if you spot any issues, please let me know.