My exhaustive testing indicated that the shortest path to the goal position in Scarne’s challenge was at least 71 moves long. I relaxed the criteria a bit, and obtained a solution which requires 72 moves, which (if I haven’t made an off by one error, still checking that out) is an actual minimal cost solution!

This solution doesn’t actually include the 5 hopping moves at the beginning (it complicates the calculation of the heurstic values and slows down the search), but I suspect I’ll get that figured out someday soon. Enjoy!

After running all night, I can assert with confidence that there are no paths of length 71 or less. I’m obviously not going to get to the ~100 move mark with the current heuristic and transposition tables alone.

Addendum: I’ve actually just got a version of the game which doesn’t include the initial five “hopping” moves. I need to work on appropriate heuristics that take into account these initial five moves and create an appropriate move generator soon.