I have a question that I've been asking for years that is somewhat domain-specific, but should be answerable by anyone who knows what a set/map are. About 20% o

I have a question that I've been asking for years that is somewhat domain-specific, but should be answerable by anyone who knows what a set/map are. About 20% of people get past "stage 1" within 5 minutes, usually people with finance/trading experience, and some will say "oh, I implemented something just like this a few years ago." Some people take 30 minutes and do ok, and some never finish. When someone tells me they have had this problem before, I tell them it should be really easy for them then, and we can move on to more interesting things! For those that DO get past stage one, it is a boss with multiple health bars. We talk about what improvements could be made, then what improvements on THOSE improvements. We keep digging until we are out of ideas. The best candidates are the ones that stump me, or introduce new ideas. I present this problem as a pair problem solving challenge, so there is no one right answer, and has a lot of back and forth.