> that isn't memoizing an array map
"memoizing" is a pretty computer-sciencey word, so not implementing a data structure exactly, but still requires knowledge beyond "plug these APIs together."
> The only time I even needed algorithmic complexity was implementing a drag and drop control, for a list that could have several hundred thousand elements, and my naive implementation was n^2.
And if you didn't have an intuition for algorithmic complexity, how long would it have taken you to figure out the problem? And how many times have you instinctively avoided having an explosion in algorithmic complexity, by intuitively picking a suitable data structure or algorithm?