https://leetcode.com/problems/design-underground-system/description/class UndergroundSystem: def __init__(self): self.checkInMap = {} # id -> (startStation, time) self.totalMap = {} # (start, end) -> [totalTime, count] def checkIn(self, id: int, stationName: str, t: int) -> None: self.checkInMap[id] = (stationName, t) def checkOut(self, id: int, stationName: str, t:..