Problem E. Cosmic Rays from last Div1 + Div2 Round had an interesting application of stack. So, I created a video editorial to help you visualize stack problems using graph modelling.
https://youtu.be/l2LTxerp2KE?si=FQzjaNj1Y-QiMH1V
I also created a practice contest https://codeforces.net/group/7Dn3ObOpau/contest/542909