It has happened a few times that I have answered a question where the author is doing things in a round-about and complicated way. I tell author that there is a better way and show them how using a short snippet with the general approach, showing key ideas and solutions. And oftentimes, I leave the rest to the author.
Most of the time, the author appreciates the review, and goes about improving their code merrily. But every now and then there is someone that insists I provide a complete working, tested implementation for them. When this happens I feel as if I'm being used as a free-of-charge contractor. I tell them (albeit in a more polite manner) that:
I'm not your contractor, figure it out.
The question I want to ask is, is it OK to do a review and not give a fully working implementation, i.e. with "some assembly required"? Or can I expect the author to fill in the blanks if I show them the way?