Is it possible to have a clue regarding the final validator? My solution passes all four tests as well as validators 1/2/3, so it’s really hard to understand what I’m missing… I don’t know if there is some trick configuration not covered by the tests (as was the case in Haunted Manor), a validator error (as was the case in Heart Of The City), or if my algorithm is just not robust enough.
There’s quite a bit of discussion in another forum thread which is also about the same puzzle. I’ve just moved the discussion from there to here. Please check out the earlier discussion here again - now you should find many custom cases to help debug your code, and also a hint about Validator 4.