Library Sorting and Checkout | Dataford Interview Questions

Your question is Library Sorting and Checkout. Start with the requirements on the right.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Zendesk Guide needs a small in-memory book catalog that supports predictable browsing and checkout processing. Given a list of books, sort them by title or author, then process checkout requests in order.

Implement a function that returns the sorted catalog, the IDs successfully checked out, and the IDs that could not be checked out because the book was already unavailable.

Formal Specification

Implement process_books(books, sort_by, checkout_ids).

books is a list of dictionaries. Each dictionary contains:
- id: a unique string
- title: a string
- author: a string
- available: a boolean
sort_by is either "title" or "author".
checkout_ids is a list of book IDs processed from left to right.
Return a dictionary with:
- books: the catalog sorted by the selected field, then by title, then by ID
- checked_out: IDs successfully checked out
- unavailable: IDs rejected because they were already checked out

The input list must not be modified. A repeated checkout request for the same book is rejected after its first successful checkout.

Constraints

1 <= len(books) <= 10^5
0 <= len(checkout_ids) <= 10^5
IDs, titles, and authors are non-empty strings
Book IDs are unique
Every checkout ID exists in the catalog
sort_by is either title or author

Function Signature

def process_books(books, sort_by, checkout_ids):