Knowing that O(n2) is a problem and that an O(n) algorithm exists matters. But why do they have to know how to write that O(n) themselves? It's a quick easy t

Knowing that O(n2) is a problem and that an O(n) algorithm exists matters. But why do they have to know how to write that O(n) themselves? It's a quick easy test of understanding, but why not ask "How would you speed this up" and show them some O(n2) code?