1396. Design Underground System

underground_system.js

class UndergroundSystem {
    #stationTripLengthMap;
    #inFlightTrips;

    constructor() {
        this.#stationTripLengthMap = {};
        this.#inFlightTrips = {};
    }

    checkIn(id, stationName, t) {
        this.#inFlightTrips[id] = [stationName, t];
    }

    checkOut(id, stationName, t) {
        const [startingStation, startTime] = this.#inFlightTrips[id];
        const tripTime = t - startTime;

        delete this.#inFlightTrips[id];

        const stationTripLength = this.#stationTripLengthMap?.[startingStation];

        if (!stationTripLength) {
            this.#stationTripLengthMap[startingStation] = {
                [stationName]: [tripTime],
            };

            return;
        }

        if (Array.isArray(stationTripLength?.[stationName])) {
            stationTripLength[stationName].push(tripTime);
        } else {
            stationTripLength[stationName] = [tripTime];
        }
    }

    getAverageTime(startStation, endStation) {
        const tripTimes = this.#stationTripLengthMap[startStation]?.[endStation];

        const totalTripTime = tripTimes.reduce((total, tripTime) => {
            return total + tripTime;
        }, 0);

        return totalTripTime / tripTimes.length;
    }
}

/**
 * Your UndergroundSystem object will be instantiated and called as such:
 * var obj = new UndergroundSystem()
 * obj.checkIn(id,stationName,t)
 * obj.checkOut(id,stationName,t)
 * var param_3 = obj.getAverageTime(startStation,endStation)
 */