Blizzard Entertainment interview question

The programming test defined a data structure incorrectly. I solved the problem as defined, but the debrief ran into a roadblock because the programmers were expecting a solution based on a different definition of that data structure. Once I realized that had happened, I tried to come up with a solution on the spot. This was a good opportunity to show my ability to think on my feet, but involved some awkward back and forth as neither set of folks realized the disconnect right away.