1396. Design Underground System

https://leetcode.com/problems/design-underground-system/description/

solution

class UndergroundSystem:
    def __init__(self):
        self.station_id_dict = {}
        # 两个int 字典，一个记录总时长，一个记录总个数，可以进一步优化空间
        self.station_duration_dict = collections.defaultdict(list)

    def checkIn(self, id: int, stationName: str, t: int) -> None:
        self.station_id_dict[id] = (stationName, t)

    def checkOut(self, id: int, stationName: str, t: int) -> None:
        in_station, in_t = self.station_id_dict.pop(id)
        self.station_duration_dict[(in_station, stationName)].append(t - in_t)

    def getAverageTime(self, startStation: str, endStation: str) -> float:
        time_list = self.station_duration_dict[(startStation, endStation)]
        return sum(time_list) / len(time_list)

时间复杂度：O(1) 空间复杂度：O()