How should I practice CD Rental System?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Okta online assessment problems in FastPrep.

Is CD Rental System associated with Okta?

FastPrep tags this as a Okta coding interview or online assessment practice problem when the problem catalog has that company context.

Problem · Design

CD Rental System

Learn this problem

● MediumOktaFULLTIMEONSITE INTERVIEW

Problem statement

Design a small in-memory CD rental system.

You are given an initial list of CD inventory entries. Each entry is [shop, cd, price], meaning shop shop owns one copy of CD cd with rental price price.

The system then receives commands. Return one output string for each command.

Commands

SEARCH|cd: return all shops that currently have CD cd available, sorted by price ascending, then shop id ascending. Return the shop ids as a single space-separated string. If no shop has an available copy, return EMPTY.
RENT|shop|cd: rent CD cd from shop. This succeeds only if that shop currently has an available copy of that CD. Return OK on success or INVALID otherwise.
UNRENT|shop|cd: return CD cd to shop. This succeeds only if that CD was previously rented from that shop and has not already been returned. Return OK on success or INVALID otherwise.

What the interview report shared

The interview report described an onsite Java and DSA/LLD round where the candidate had to design and implement a CD rental system. It shared the initial data shape [shop, cd, price], the search(cd) API sorted by price then shop id, and the rent(shop, cd) and unrent(shop, cd) APIs with availability checks. The report did not specify command serialization, exact return strings, or sample inputs.

How FastPrep adapted it

FastPrep turned the class-style interview task into a single command-processing function. The OK, INVALID, and EMPTY outputs are practice scaffolding based on the reported APIs, not exact original wording.

Function

processCdRentalCommands(entries: String[][], commands: String[]) → String[]

Examples

Example 1

entries = [["1","10","5"],["2","10","4"],["1","20","6"]]commands = ["SEARCH|10","RENT|2|10","SEARCH|10","RENT|2|10","UNRENT|2|10","SEARCH|10"]return = ["2 1","OK","1","INVALID","OK","2 1"]

Before any rental, CD 10 is available at shop 2 for price 4 and shop 1 for price 5, so shop 2 comes first. After renting from shop 2, only shop 1 remains available until the CD is returned.

Example 2

entries = [["3","7","8"],["4","7","8"],["5","8","2"]]commands = ["SEARCH|7","RENT|4|7","SEARCH|7","UNRENT|3|7","UNRENT|4|7","SEARCH|7","SEARCH|9"]return = ["3 4","OK","3","INVALID","OK","3 4","EMPTY"]

Shops 3 and 4 have the same price for CD 7, so the smaller shop id comes first. Returning from shop 3 is invalid because that copy was never rented.

Constraints

1 <= entries.length <= 100000
1 <= commands.length <= 100000
Each [shop, cd] pair appears at most once in entries.
1 <= shop, cd, price <= 10^9
Commands are always one of SEARCH, RENT, or UNRENT with the field counts shown above.