As I was walking to get my turkey pot pie today that was cooking in the microwave in our break room, I looked at the parking lot below and realized that parking lots are approximately perfect hash functions.
Think about it: cars come in in some semi-random order; spaces are available in semi-random fashion; cars park; and the owner comes back to the same spot to retrieve the item later. Admittedly, it isn’t necessarily replicable every day – but it’s an approximation.
Perhaps a better example would be a professor who tells his students on the first day of class to remember where they are sitting, because that’s their seat for the rest of the semester. The spaces were filled in random fashion once, then always in the same way in the future: if Sarah isn’t in class, her slot is empty – it doesn’t get filled by anyone else because they’re in their slots.
The real trick will be to figure out how to replicate this behavior functionally.