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Design Underground System

Bloomberg LP● MediumNEW GRADPHONE SCREENONSITE INTERVIEW

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Problem statement

Process operations for an underground transit system.

["checkIn", id, station, time] records that passenger id entered station at integer time.
["checkOut", id, station, time] completes that passenger's active trip.
["getAverageTime", start, end] asks for the average duration of every completed trip from start to end.

Return the answers to the average-time operations in encounter order. Trips in the reverse direction belong to a different route.

Function

undergroundSystem(operations: String[][]) → double[]

Examples

Example 1

operations = [["checkIn","45","Leyton","3"],["checkIn","32","Paradise","8"],["checkOut","45","Waterloo","15"],["checkOut","32","Cambridge","22"],["getAverageTime","Paradise","Cambridge"],["getAverageTime","Leyton","Waterloo"]]return = [14.0,12.0]

The completed trips last 22-8=14 and 15-3=12 time units.

Example 2

operations = [["checkIn","1","A","2"],["checkOut","1","B","8"],["checkIn","2","A","10"],["checkOut","2","B","20"],["getAverageTime","A","B"]]return = [8.0]

The two durations are 6 and 10, so their average is 8.

Constraints

1 <= operations.length <= 10^5.
Passenger IDs and times are decimal integers encoded as strings.
Every check-out has one active matching check-in, and an ID has at most one active trip.
Every average-time query has at least one completed matching route.
Times are strictly increasing within each passenger's trip.