Practical Simulations

A Stripe practical prompt rarely ends where it starts. You open on a CSV that needs cleaning, and three parts later you are running depth-first search over a directed graph you built out of one of its columns. That climb, from parsing to a graph search on the same data, is a reported Stripe experience, and the currency problem in the practical-coding lesson never reaches it. The other shape below is missing too. None of the parsing problems in that lesson asks you to run a live system forward one event at a time and say where it lands.

So this lesson works all three. The first problem validates a file and then hunts a circular dependency hiding inside one of its columns. The second steps a Premium question through a stream of add, remove and request events and asks for the final assignment of sessions to servers. Problem three lays a repeating week out as a single minute-of-week axis and schedules a deploy across time zones and freeze windows, where the Sunday-to-Monday seam is the edge that bites. Read each prompt, try it in the editor, then reveal the walkthrough.

The Stripe angle

Model the data cleanly in Part 1, so each escalation lands as a small change in all three problems. In the first, the field-to-dependency map you build to validate rows is the exact adjacency map the cycle search walks, so the graph is already sitting there when the interviewer asks for it. In the second, two small structures, a set of live servers and a session-to-server map, hold enough that a graceful shutdown can reassign work without special-casing anything. For the third, laying every team's window onto one minute-of-week axis turns the time zones into a single subtraction each. Keep money and counts as integers, and keep every output sorted. Write the assertions yourself, so the off-by-one surfaces before the interviewer finds it.