I think it takes more than an hour to make something production-ready. Setting up test cases and tracing down memory errors and leaks is going to take a while, even (and I would think especially) for an experienced C programmer.
What memory errors and leaks? A good coder should be able to produce error-free code on first try, provided the documentation is clear and correct, and the problem is sufficiently simple (as in this case).
Tests and debugging will only get you so far, theoretical methods can get you farther in terms of correctness (provided your compiler isn't broke etc).
Quoting Linus Torvalds: "Don't just make random changes. There really are only two acceptable models of development: "think and analyze" or "years and years of testing on thousands of machines". Those two really do work."
Okay, maybe I should rephrase it. It takes more than an hour to carefully think and analyze, and then implement the thing, and then make sure there aren't any bugs. Thinking things through beforehand makes the possibility of errors less likely, but even then you may have made a silly mistake at some point or another. That is why we have things like unit tests and code reviews, because even the best programmers make mistakes. I certainly wouldn't trust C code written by a single developer in one hour to be production-ready.
I can rephrase as well. I'm not going to rush your interview code to production, but the review cycle needs to start with a first version. We'll refine as needed, but this is a simple enough problem to expect well-structured code in one hour.
