How should I practice In-Memory URL Shortener?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Revolut phone screen problems in FastPrep.

Is In-Memory URL Shortener associated with Revolut?

FastPrep tags this as a Revolut phone screen coding practice problem when the problem catalog has that company and stage context.

Problem · Design

In-Memory URL Shortener

Learn this problem

● Medium

RevolutFULLTIMEPHONE SCREEN

Problem statement

Implement the core of an in-memory URL shortener. The service starts empty and processes operations from left to right. The parallel values array supplies each operation's argument.

shorten receives a long URL. If the URL has appeared before, return its existing token. Otherwise assign the next positive integer ID, starting at 1, encode it in Base62 using the alphabet 0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ, store both directions of the mapping, and return the token.
restore receives a token returned by an earlier shorten operation and returns its original long URL.

Return one string result for every operation, in order. Tokens are path components only; do not prepend a domain.

Function

runUrlShortener(operations: String[], values: String[]) → String[]

Examples

Example 1

operations = ["shorten","shorten","restore","shorten","restore"]values = ["https://example.com/articles/alpha","https://example.com/docs/beta","1","https://example.com/articles/alpha","2"]return = ["1","2","https://example.com/articles/alpha","1","https://example.com/docs/beta"]

The first two distinct URLs receive tokens 1 and 2. Restoring token 1 returns the first URL, and shortening that URL again reuses token 1.

Example 2

operations = ["shorten","shorten","shorten","shorten","shorten","shorten","shorten","shorten","shorten","shorten","restore"]values = ["u1","u2","u3","u4","u5","u6","u7","u8","u9","u10","a"]return = ["1","2","3","4","5","6","7","8","9","a","u10"]

The tenth positive ID is encoded as a in the declared Base62 alphabet, and restoring that token returns the tenth URL.

Constraints

1 <= operations.length <= 2 * 10^5
values.length == operations.length
Each operation is exactly shorten or restore.
A long URL is nonempty and has length at most 2000.
Every restore token was returned by an earlier shorten operation in the same batch.