LC 1396. Design Underground System
https://leetcode.com/problems/design-underground-system/
Clarification & Assumption
Description: design an underground railway system that keeps track
of customer travel times between different stations
functions:
1. void checkIn(int id, String stationName, int t)
customer with id check in stationName at time t
2. void checkOut(int id, String stationName, int t)
customer with id check out stationName at time t
3. double getAverageTime(String startStation, String endStation)
calculate the average time it takes to traverl from start to end stations