I've found a very simple question that weeds out about 75% of applicants:
"You have a bunch of objects which have an implicit ordering. You want to insert them into a collection, look them up, and retrieve the smallest/biggest one as quickly as possible."
You'd be amazed at how many people suggest hash tables.
"You have a bunch of objects which have an implicit ordering. You want to insert them into a collection, look them up, and retrieve the smallest/biggest one as quickly as possible."
You'd be amazed at how many people suggest hash tables.