Well that's gonna keep the CPU time down!

There are IRL situations where 00009 could be an expected input but 00010 would not be a valid result, if you were mediating between two APIs is just one example. Situations where requirements will not always be explictly stated...

Cool Kata. Based on the sample test, I assumed both players used the same board token (I don't remember ever playing this game), so I ended up googling the rules and reimplementing for independent tokens. There's also a little ambiguity between "may" and "must" climb a ladder when landing on it's bottom square. I suppose there could be a strategic case for skipping a ladder to get to a better one?

This does not enforce the requirement that s is built from characters drawn from part1 or part2, in the order in which they occur. 's' must be found AFTER 'r'!