Zero initial capacity
A lot that starts at capacity 0 rejects every car of that type immediately.
Three counters. One decision per car.
A multi-level parking garage reserves separate floors for big vehicles, medium sedans, and compact cars — each with a fixed number of spots. When a vehicle arrives, the attendant checks that floor's counter: if a spot remains, park and decrement; otherwise, turn the vehicle away. Three counters, one decrement per arrival, one comparison per query. O(1) per operation.
Watch the algorithm run
Independent Buckets
Each car type maps to exactly one counter. A big car cannot take a medium slot. The system is three independent decrement-or-reject counters — no cross-type borrowing.
The common mistake is using a boolean "has space" flag instead of an integer count. A boolean forgets that capacity can be greater than one.
Algorithm
Three independent counters, each decremented on arrival. No search, no sorting — just an array lookup and a decrement.
-
1
Initialize counters
Store three counters —
big,medium,small— set to the capacity of each lot. -
2
Receive a car
On each
addCar(type)call, check the counter for the given type. -
3
Accept or reject
If the counter is positive, decrement it and return
true. Otherwise returnfalse.
Edge Patterns
Understanding boundary behavior is as important as the main algorithm path.
Mixed availability
One lot may be full while others have space. Each type is tracked independently.
Complexity
Time: O(1) per AddCar — single array lookup and decrement.
Space: O(1) — three integer counters.