[kelnos]

> I once got a whiteboarding problem and proposed a solution, and the interviewer gave me a flat out "that's not the one I had in mind"

Oh jeez. The impatient, combative side of me would want to respond, "so you're not open to other people's ideas, or open to the possibility that your approaches may not be the only good possibilities?"

A more diplomatic response might be, "can you tell me what you think about my approach is unworkable or at least suboptimal?" I think your question about a possible missing constraint/requirement was a good one. Actually, I think after asking that question and getting no reasonable responses, my original combative response seems a bit more appropriate...