I almost gave up on this one but finally succeeded as my last-but-one (see Day22)
puzzle. For some reason, I really had a hard time wrapping my head around this puzzle.
The trick was using a PriorityQueue and clever caching (dynamic programming) as
so often with this kind of way-finding-challenges.
There was absolutely no way I could have solved the second part of that puzzle. despite of wasting many hours on the problem. I went to the forums and more or less copied a working version. This was a big bummer since it was the final and 300th star missing for me. "Achieving" it that way just felt dirty and not the least bit satisfying.