Worked through the problem, with the interviewers as 'team-members', without them helping too much. I asked questions, provided assumptions about the problem, etc., and they would agree or point out possible 'bugs' in my solution. Once I worked through it enough to get a solution to the simple case provided, they would add complexity to it. We iterated like this for a while to make my solution more robust. Near the end of that interview, they gave me a hint, which allowed me to find the optimal solution. Very fun interview in a friendly, relaxed environment.