The Lost Library Cards

Every borrowed book should come back — compare the borrowed list against the returned pile. 📚

You get the borrowed book ids and the returned ids (returns may include weird extras — ignore those). Print the still-missing ids in alphabetical order, space-separated, or all returned.

Example:

Input: borrowed = ["b12", "a07", "c33"], returned = ["a07"] Output: b12 c33

set(borrowed) - set(returned) removes "a07", leaving "b12" and "c33" still missing.