This problem was similar to the Marble Game on day 9, so I started with a solution similar to the one I used for that problem, using a linked list and having the two elves as linked list nodes that can move along the list. It worked fine for the first part of the problem, but started running pretty slow for the second part of the problem.
Nice little problem with a more complicated description but a somewhat simple solution.
This is the first problem that I still haven't an efficient way to solve the second part.
Another harder problem. The first part was pretty simple and didn't take me too much time to solve, but adapting for the second part of the problem took a lot more time.
So this one really took me by surprise at the start and had me trying a lot of different stuff to find the best solution.