Edit: Ok, let me add some nuance here. I think we both probably agree that implementing a shortest path algo perfectly in an interview setting is beyond reasonable or useful. But I would expect an engineer to be able to have a discussion about it that shows me they understand the basic concepts and given google and a bit of time could relearn that. But without the complexity of shortest path I would not expect basic BFS to be outside of the scope of an interview. I guess that's just where I draw my lines.