Not a live preview and not a button-counter demo at the end, but the overall structure and the whole O(n) vs O(n^2) argumentation was in this blog post from a now defunct domain. Maybe this is what you were looking for:
This definitely looks different, and I don't recall seeing this before. But this is a great post! It communicates some of the very important ideas in a straightforward way. Thanks!
https://web.archive.org/web/20150414080539/http://hackflow.c...