LeetCode in Kotlin

1396. Design Underground System

Medium

An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another.

Implement the UndergroundSystem class:

You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2, then t1 < t2. All events happen in chronological order.

Example 1:

Input [“UndergroundSystem”,”checkIn”,”checkIn”,”checkIn”,”checkOut”,”checkOut”,”checkOut”,”getAverageTime”,”getAverageTime”,”checkIn”,”getAverageTime”,”checkOut”,”getAverageTime”] [[],[45,”Leyton”,3],[32,”Paradise”,8],[27,”Leyton”,10],[45,”Waterloo”,15],[27,”Waterloo”,20],[32,”Cambridge”,22],[“Paradise”,”Cambridge”],[“Leyton”,”Waterloo”],[10,”Leyton”,24],[“Leyton”,”Waterloo”],[10,”Waterloo”,38],[“Leyton”,”Waterloo”]]

Output: [null,null,null,null,null,null,null,14.00000,11.00000,null,11.00000,null,12.00000]

Explanation:

UndergroundSystem undergroundSystem = new UndergroundSystem();
undergroundSystem.checkIn(45, "Leyton", 3);
undergroundSystem.checkIn(32, "Paradise", 8);
undergroundSystem.checkIn(27, "Leyton", 10);
undergroundSystem.checkOut(45, "Waterloo", 15); // Customer 45 "Leyton" -> "Waterloo" in 15-3 = 12
undergroundSystem.checkOut(27, "Waterloo", 20); // Customer 27 "Leyton" -> "Waterloo" in 20-10 = 10
undergroundSystem.checkOut(32, "Cambridge", 22); // Customer 32 "Paradise" -> "Cambridge" in 22-8 = 14
undergroundSystem.getAverageTime("Paradise", "Cambridge"); // return 14.00000. One trip "Paradise" -> "Cambridge", (14) / 1 = 14
undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000. Two trips "Leyton" -> "Waterloo", (10 + 12) / 2 = 11
undergroundSystem.checkIn(10, "Leyton", 24);
undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000
undergroundSystem.checkOut(10, "Waterloo", 38); // Customer 10 "Leyton" -> "Waterloo" in 38-24 = 14
undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 12.00000. Three trips "Leyton" -> "Waterloo", (10 + 12 + 14) / 3 = 12 

Example 2:

Input [“UndergroundSystem”,”checkIn”,”checkOut”,”getAverageTime”,”checkIn”,”checkOut”,”getAverageTime”,”checkIn”,”checkOut”,”getAverageTime”] [[],[10,”Leyton”,3],[10,”Paradise”,8],[“Leyton”,”Paradise”],[5,”Leyton”,10],[5,”Paradise”,16],[“Leyton”,”Paradise”],[2,”Leyton”,21],[2,”Paradise”,30],[“Leyton”,”Paradise”]]

Output: [null,null,null,5.00000,null,null,5.50000,null,null,6.66667]

Explanation:

UndergroundSystem undergroundSystem = new UndergroundSystem();
undergroundSystem.checkIn(10, "Leyton", 3);
undergroundSystem.checkOut(10, "Paradise", 8); // Customer 10 "Leyton" -> "Paradise" in 8-3 = 5
undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.00000, (5) / 1 = 5
undergroundSystem.checkIn(5, "Leyton", 10);
undergroundSystem.checkOut(5, "Paradise", 16); // Customer 5 "Leyton" -> "Paradise" in 16-10 = 6
undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.50000, (5 + 6) / 2 = 5.5
undergroundSystem.checkIn(2, "Leyton", 21);
undergroundSystem.checkOut(2, "Paradise", 30); // Customer 2 "Leyton" -> "Paradise" in 30-21 = 9
undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 6.66667, (5 + 6 + 9) / 3 = 6.66667 

Constraints:

Solution

class UndergroundSystem {
    private class StationAndTime(var station: String, var time: Int)

    private val averageTimeMap: MutableMap<String, DoubleArray>
    private val travelerMap: MutableMap<Int, ArrayList<StationAndTime>>

    init {
        averageTimeMap = HashMap()
        travelerMap = HashMap()
    }

    fun checkIn(id: Int, stationName: String, t: Int) {
        travelerMap.putIfAbsent(id, ArrayList())
        travelerMap[id]!!.add(StationAndTime(stationName, t))
    }

    fun checkOut(id: Int, stationName: String, t: Int) {
        val list = travelerMap[id]!!
        val stationAndTime = list.last()
        val startToEndStation: String = stationAndTime.station + "->" + stationName
        val duration: Int = t - stationAndTime.time
        if (averageTimeMap.containsKey(startToEndStation)) {
            val pair = averageTimeMap[startToEndStation]
            val newAverage = (pair!![0] * pair[1] + duration) / (pair[1] + 1)
            averageTimeMap[startToEndStation] = doubleArrayOf(newAverage, pair[1] + 1)
        } else {
            averageTimeMap[startToEndStation] = doubleArrayOf(duration.toDouble(), 1.0)
        }
    }

    fun getAverageTime(startStation: String, endStation: String): Double {
        return averageTimeMap["$startStation->$endStation"]!![0]
    }
}
/*
 * Your UndergroundSystem object will be instantiated and called as such:
 * var obj = UndergroundSystem()
 * obj.checkIn(id,stationName,t)
 * obj.checkOut(id,stationName,t)
 * var param_3 = obj.getAverageTime(startStation,endStation)
 */