Bike Share: Fares, Full Stations and Day Passes

Bike Share: Fares, Full Stations and Day Passes

You've joined the platform team behind a city bike-share app. Riders unlock a bike at one docking station and return it to another. Support is flooded with fare complaints and wrong "bikes available" numbers, and the product team has two changes queued behind them. You have three Parts, and each builds on the previous one. All money is integer cents and all times are integer seconds.

Codebase

How your code is run

run(operations: list[list]) -> list executes the operations in order against a fresh system and returns one result per operation. Every operation is [name, ts, ...args]. Errors are returned as "error: <code>" strings, never raised.

• A wrong number of arguments, a non-integer ts, an empty or non-string id, a capacity that is not an integer > 0, a non-boolean flag, or an unknown bike kind returns "error: invalid arguments". An unknown operation name returns "error: unknown operation".
• Ride ids count up in the order unlocks succeed. A rider has at most one open ride.
• A bike is docked (it sits in a dock of exactly one station) or out on a ride. unlock takes the bike out of its dock. dock puts it into a dock at the given station; broken: true reports it as broken at return, and it stays broken until repair. A rider can unlock only a docked bike that is not broken (bike unavailable otherwise). A rider may return a bike to the station it came from.
• station_status fields: capacity; bikes = bikes in docks (broken ones included); available = docked bikes that are not broken; free = capacity - bikes.
• dock and rider_total charge the fare to the rider. rider_total is the sum of everything billed.

Tariff

• Unlock fee: 100c per ride; members pay none.
• Time charge: the ride lasts dock_ts - unlock_ts seconds, and every *started* minute is billed: 0s is 0 minutes, 1s to 60s is 1 minute, 61s is 2 minutes. Each billed minute costs 15c (base rate).
• Members ride the first 45 billed minutes of each ride at no base rate, then pay 15c for every minute beyond 45 (45 min = 0c, 46 min = 15c).
• E-bikes add a 25c surcharge for every billed minute, for members and non-members alike, including a member's free minutes.

Example: a non-member on a classic bike for 20 minutes pays 100 + 20x15 = 400. A member on an e-bike for 50 minutes pays 5x15 + 50x25 = 1325.

Part 1 - Fix the fare and availability bugs (about 10 min)

Support has three reports: "I was charged an extra minute on a ride of exactly one hour", "I'm a member and a 46-minute ride cost me the whole 46 minutes", and "the app said 3 bikes were available but two were broken". Make the system follow the rules above. tests/test_rides.py has one failing test to start from.

Worked example (stations A and B with 4 docks each; ann non-member, mo member; b1 classic and e1 e-bike docked at A, plus a second classic b2 at A that nobody touches):

["unlock", 100, "ann", "b1"]        -> "r-1"
["dock", 1300, "ann", "B", false]   -> 400
["unlock", 2000, "mo", "e1"]        -> "r-2"
["dock", 5000, "mo", "B", false]    -> 1325
["station_status", 5001, "B"]       -> {"capacity": 4, "bikes": 2, "available": 2, "free": 2}
["unlock", 6000, "ann", "b1"]       -> "r-3"
["dock", 6061, "ann", "A", true]    -> 130        # 61s = 2 minutes: 100 + 30
["station_status", 6062, "A"]       -> {"capacity": 4, "bikes": 2, "available": 1, "free": 2}

Part 2 - Full stations and the grace period (about 15 min)

Today dock ignores capacity. Make a rider who arrives at a full station bounce off it without being penalised for the search.

1. dock at a station with no free dock returns "error: station full", checked after station not found. The ride stays open and the bike stays out; nothing else about the bike (including its broken flag) or the station changes.
2. The first bounce of a ride records its ts as that ride's *grace start*. Later bounces of the same ride do not move it.
3. When the ride finally docks successfully at ts, the forgiven time is min(ts - grace_start, 600) seconds. Subtract it from ts - unlock_ts before rounding up to billed minutes, then price as usual.
4. A ride that never bounced gets no grace. Grace belongs to one ride only.
5. A bike reported broken at return still occupies its dock (it counts in bikes, not in available), and a repaired bike keeps its dock.

Worked example (station F has capacity 1 and is already full of f1; ann is a non-member):

["unlock", 100, "ann", "b1"]        -> "r-1"
["dock", 1000, "ann", "F", false]   -> "error: station full"   # grace starts at 1000
["dock", 1100, "ann", "F", false]   -> "error: station full"
["dock", 1300, "ann", "A", false]   -> 325   # 1200s - min(300, 600) = 900s = 15 min: 100 + 225

Part 3 - Day passes (about 15 min)

Product wants a day pass for non-members: 1200c for unlimited rides within 24 hours, where each ride's first 30 minutes are free. This changes how a ride is priced, so rework the fare design rather than bolting a special case on.

1. buy_pass charges 1200c to the rider and returns 1200. Errors in order: rider not found, already a member (members cannot buy passes), pass already held.
2. A pass is *held* from purchase until its window closes. It is not tied to the purchase time: the window starts at the rider's next successful unlock at time S and covers unlocks at ts with S <= ts < S + 86400 (half-open). A failed unlock does not start it.
3. A ride is pass-covered if its unlock happened inside the window (the unlock that starts the window is covered). This is decided at unlock and does not change if the ride ends after the window closes.
4. A pass-covered ride pays no unlock fee and gets 30 free base-rate minutes (instead of the member's 45). Beyond them each billed minute costs 15c. The e-bike surcharge still applies to every billed minute. Billed minutes are computed as in Parts 1 and 2, including grace.
5. Once the window has closed the pass is no longer held: unlocks are priced normally and the rider may buy another. A bought-but-unused pass counts as held.

Worked example (ann non-member, mo member, bikes as in Part 2):

["buy_pass", 10, "ann"]             -> 1200
["buy_pass", 11, "ann"]             -> "error: pass already held"
["buy_pass", 12, "mo"]              -> "error: already a member"
["unlock", 100, "ann", "b1"]        -> "r-1"      # window is [100, 86500)
["dock", 2500, "ann", "A", false]   -> 150        # 40 min: 10 paid minutes x 15
["unlock", 3000, "ann", "e1"]       -> "r-2"
["dock", 4800, "ann", "A", false]   -> 750        # 30 min free base, e-bike 30 x 25
["unlock", 86500, "ann", "b1"]      -> "r-3"      # window closed: normal pricing
["dock", 86560, "ann", "A", false]  -> 115        # 1 min: 100 + 15
["rider_total", 86561, "ann"]       -> 2215

Hidden tests re-check every earlier Part after the later ones, so keep Parts 1 and 2 behaviour intact.