Vector.toSet for easy comparison
renaming
pathSets implemented as a stream
YEAH - Solver works - but still a little slow
"optimized" from 28s to 26s :-/ need to check for performance-bottleneck
JVisualVm: optimized from 30s to 22s
unecessary zip removed
improved another 5s --> from 21s to 16s. UnblockMeSolver.arePiecesOverlapping is still problematic