[lukesandberg]

Iterative is definitely the way to go, and it's the way you are (generally) expected to answer a question. If you are asked a question a good first approach is almost always to describe the simplest/dumbest solution you can and then iterate to a better one.

The whole point of the coding interview is to ensure that 1. you actually know how to code and 2. that you have reasonable problem solving skills. By iteratively approaching the problem you demonstrate your problem solving and communication skills. Also a good interviewer will usually structure a problem so that you have to approach it iteratively because they keep adding restrictions/requirements after each time you solve it.