If this (finishing a program missing only a few lines of code) were all most coding interviews were, I don't think there'd be anywhere near as many complaints about them. That's very similar to what you'd actually be doing on the job.
It's coming up with what you took in your data structures/algorithms class a decade ago on the spot and write full functions about them, especially on a whiteboard, that gets really annoying, and makes programmers feel like they have to refresh their knowledge of an entire class (plus a bunch of other trivia from across CS) every time they want to find a new job.
It's coming up with what you took in your data structures/algorithms class a decade ago on the spot and write full functions about them, especially on a whiteboard, that gets really annoying, and makes programmers feel like they have to refresh their knowledge of an entire class (plus a bunch of other trivia from across CS) every time they want to find a new job.