Museum Timed Entry: Tickets, Special Exhibition and Weekend Crowds

Museum Timed Entry: Tickets, Special Exhibition and Weekend Crowds

You've joined the visitor-experience team at an art museum. Entry is by timed slot: every day has fourteen entry slots, one every 30 minutes from 10:00 to 16:30, and each slot can only take so many people. The booking service is live but front-desk staff have reported wrong totals and a slot that "fills up" with babies. A special exhibition opens next month, and the facilities team has just told us weekends need a different crowd limit. Work through the three Parts in order. All money is integer cents; dates are YYYY-MM-DD, slots are HH:MM.

Codebase

How your code is run

run(operations: list[list]) -> list executes the operations in order against a fresh museum and returns one result per operation. Every operation is [name, now, ...args], where now is the caller's clock as "YYYY-MM-DD HH:MM" (it is only compared with slot start times). Errors are returned as strings, never raised: "error: <code>", e.g. "error: slot full".

• An unknown operation name returns "error: unknown operation". A wrong number of arguments, a now that is not a real YYYY-MM-DD HH:MM, or an operation that is not a list returns "error: invalid arguments" (unknown name is checked first).
• capacity must be an integer >= 1 (true/false are not integers).
• Order ids are "MT-1", "MT-2", ... in the order orders succeed; a rejected order uses no id.
• availability and day_report ignore now. A day can be opened for any date, past or future.
• day_report covers the orders on that date that have not been refunded: orders is how many, headcount is every person including children under 5, revenue is the sum of their totals.

---

Part 1 - Fix the ticket counting and pricing

Front desk reports three problems. Find and fix them; do not change any other behaviour. tests/test_service.py has a failing test to start from.

Rules

1. A ticket is "adult", "senior", "member", "guest" or "child:<age>" where age is a whole number 0-17 written without leading zeros. Anything else (wrong case, "child", "child:18", "child:07", a non-string) is invalid ticket, and one bad ticket rejects the whole order.
2. Prices: adult 2400, senior 1800, child aged 5-17 1200, child under 5 free, member free, guest 1500.
3. Each member in the order may bring up to 2 guests at the guest price. Guests beyond 2 x members pay the adult price. With no member in the order, every guest pays adult.
4. Capacity is per slot. Every ticket takes one place except children under 5, who take none (members and guests do take places). An order is all-or-nothing: if its places do not fit in the slot's remaining places, nothing is booked and the result is slot full. An order that fits exactly is accepted; an order that takes zero places is always accepted, even in a full slot.
5. refund returns the whole order total and puts its places back. It works only while now is strictly before the slot's start (at exactly the start time it is slot started), and an order can be refunded once.
6. slot started for book uses the same test: a slot can no longer be booked at or after its start time.

Example (capacity 6, a Friday)

["open_day", "2026-03-13 08:00", "2026-03-13", 6]                                      -> true
["book", "2026-03-13 08:00", "2026-03-13", "10:00", ["adult","child:3","child:9"]]     -> {"order":"MT-1","total":3600,"slot":"10:00"}
["book", "2026-03-13 08:00", "2026-03-13", "10:00", ["member","guest","guest","guest"]] -> {"order":"MT-2","total":5400,"slot":"10:00"}
["book", "2026-03-13 08:00", "2026-03-13", "10:00", ["adult"]]                         -> "error: slot full"
["book", "2026-03-13 08:00", "2026-03-13", "10:00", ["child:2"]]                       -> {"order":"MT-3","total":0,"slot":"10:00"}
["refund", "2026-03-13 09:59", "MT-1"]                                                 -> 3600
["book", "2026-03-13 09:59", "2026-03-13", "10:00", ["adult"]]                         -> {"order":"MT-4","total":2400,"slot":"10:00"}
["day_report", "2026-03-13 09:59", "2026-03-13"]                                       -> {"orders":3,"headcount":6,"revenue":7800}

MT-1 takes 2 places (the 3-year-old is free), MT-2 takes 4 (the third guest pays 2400, so 2 x 1500 + 2400), which fills the slot exactly.

---

Part 2 - Special exhibition

A special exhibition opens in a small gallery. Visitors can add it to any ticket, it costs extra, and the gallery has its own, smaller capacity per slot. A visitor who wants the exhibition needs room in both general admission and the exhibition for that slot.

Rules

1. open_day takes an optional fourth argument, exhibit_capacity (integer >= 0; default 0, meaning no exhibition that day). An invalid value is invalid capacity, checked after the capacity check. Exhibition capacity is per slot.
2. Any ticket may end in +x ("adult+x", "child:9+x", "guest+x") to add the exhibition. Only that exact suffix, once, is valid; anything else is invalid ticket.
3. The exhibition adds 700 per person on top of the ticket price, for every kind including members and guests. Children under 5 are still free: "child:4+x" costs nothing, takes no general place and no exhibition place.
4. book error order becomes: invalid ticket, empty order, invalid slot, day not open, slot started, then exhibit closed (the order needs exhibition places and the day's exhibit_capacity is 0), then slot full (general), then exhibit full. The order is still all-or-nothing: if the exhibition is short, no general places are kept either.
5. refund puts back both kinds of places and returns the full total including surcharges.
6. availability takes an optional second argument "exhibit" and then reports remaining exhibition places per slot. Any other second argument is invalid arguments (checked before day not open). day_report revenue includes surcharges.

Example (capacity 10, exhibit capacity 2)

["open_day", "2026-03-13 08:00", "2026-03-13", 10, 2]                                     -> true
["book", "2026-03-13 08:00", "2026-03-13", "11:00", ["adult+x","child:4+x","senior+x"]]   -> {"order":"MT-1","total":5600,"slot":"11:00"}
["book", "2026-03-13 08:00", "2026-03-13", "11:00", ["adult+x"]]                          -> "error: exhibit full"
["book", "2026-03-13 08:00", "2026-03-13", "11:00", ["adult"]]                            -> {"order":"MT-2","total":2400,"slot":"11:00"}
["availability", "2026-03-13 08:00", "2026-03-13", "exhibit"]                             -> [["10:00",2],["10:30",2],["11:00",0],["11:30",2], ...]
["refund", "2026-03-13 10:00", "MT-1"]                                                    -> 5600

MT-1 is 2400 + 1800 + 2 x 700 + 0 = 5600 and uses 2 exhibition places. The refund frees them again.

---

Part 3 - Weekend crowds and walk-up overflow

Facilities has changed the crowd limit for weekends, and the front desk wants to offer walk-ups the next free slot instead of turning them away.

Rules

1. On Saturdays and Sundays (by the calendar date), the day's capacity is no longer per slot: it is the limit for the whole clock hour. The two slots HH:00 and HH:30 share one pool of capacity places. Weekdays are unchanged. Exhibition capacity stays per slot on every day.
2. availability (general) on a weekend reports, for each slot, the places left in that slot's hour, so the HH:00 and HH:30 entries are equal. A refund returns places to that hour's pool.
3. New operation walk_up with the arguments of book (date, slot, tickets). It validates exactly like book up to and including exhibit closed. Then it tries the requested slot, and if the order does not fit (in general admission, or in the exhibition if the order needs it) it tries each later slot of the same day, in order, and books the first one where the whole order fits both pools. It returns {"order", "total", "slot"} where slot is the slot actually booked. If no slot from the requested one to 16:30 fits, it returns "error: sold out".
4. book itself never moves an order: it still returns slot full / exhibit full. Refunds, the slot started rule and day_report use the slot that was actually booked.
5. Parts 1 and 2 behave as before on weekdays; their examples use a Friday.

Example (Saturday, capacity 4)

["open_day", "2026-03-14 08:00", "2026-03-14", 4]                                    -> true
["book", "2026-03-14 08:00", "2026-03-14", "10:00", ["adult","adult","adult"]]       -> {"order":"MT-1","total":7200,"slot":"10:00"}
["book", "2026-03-14 08:00", "2026-03-14", "10:30", ["adult","adult"]]               -> "error: slot full"
["walk_up", "2026-03-14 09:50", "2026-03-14", "10:30", ["adult","adult"]]            -> {"order":"MT-2","total":4800,"slot":"11:00"}
["refund", "2026-03-14 09:55", "MT-1"]                                               -> 7200
["book", "2026-03-14 09:55", "2026-03-14", "10:30", ["adult","adult"]]               -> {"order":"MT-3","total":4800,"slot":"10:30"}

The 10:00 and 10:30 slots share the four places of the 10:xx hour, so the 10:30 order does not fit and the walk-up rolls over to 11:00, the first slot of the next hour.