HN user
I think the point is that asking a user to do this (even though they can get around it) is offensive. "Hey spam your friends and we'll give you free stuff" is starting to get too common.
actually they should be able to code all of them from scratch. They don't have to know all the details by heart or be able to come up with the concept from nothing, but if given Wikipedia as a reference, any developer worth anything should be able to implement these basic data structures and basic algorithms without much trouble.