The Repeat Visitor

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant grading.

Domain

Python

Difficulty

medium

Seniority

L4

Problem

You're combing purchase logs for a retail loyalty team, where each record carries a `user` and a `date` string in 'YYYY-MM-DD' format and the records arrive in no particular order. A user counts as a repeat visitor if two of their purchases fall no more than `days` apart on the calendar. Return the IDs of those users sorted alphabetically, and an empty list when nobody qualifies.

Summary

Loyal customers come back sooner than expected.

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