1396-DesignUndergroundSystem.go

package main

// 1396. Design Underground System
// 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:
//     void checkIn(int id, string stationName, int t)
//         A customer with a card ID equal to id, checks in at the station stationName at time t.
//         A customer can only be checked into one place at a time.
//     void checkOut(int id, string stationName, int t)
//         A customer with a card ID equal to id, checks out from the station stationName at time t.
//     double getAverageTime(string startStation, string endStation)
//         Returns the average time it takes to travel from startStation to endStation.
//         The average time is computed from all the previous traveling times from startStation to endStation that happened directly, meaning a check in at startStation followed by a check out from endStation.
//         The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation.
//         There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called.

// 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:
//     1 <= id, t <= 10^6
//     1 <= stationName.length, startStation.length, endStation.length <= 10
//     All strings consist of uppercase and lowercase English letters and digits.
//     There will be at most 2 * 10^4 calls in total to checkIn, checkOut, and getAverageTime.
//     Answers within 10^-5 of the actual value will be accepted.

import "fmt"

type StationTime struct {
    station string
    time    int
}

type UndergroundSystem struct {
    ids map[int]StationTime
    avg map[[2]string][2]int // key = [进站站名,出站站名] value = [累计用时,乘车次数]
}

func Constructor() UndergroundSystem {
    return UndergroundSystem{map[int]StationTime{}, map[[2]string][2]int{}}
}

func (this *UndergroundSystem) CheckIn(id int, stationName string, t int) {
    this.ids[id] = StationTime{stationName, t} // 记录进站信息
}

func (this *UndergroundSystem) CheckOut(id int, stationName string, t int) {
    start := this.ids[id] // 获取进站信息
    delete(this.ids, id) // 出站，删除进站信息
    key := [2]string{start.station, stationName}
    v := this.avg[key]
    // 0 记录用时 1记录次数
    this.avg[key] = [2]int{v[0] + t - start.time, v[1] + 1}
}

func (this *UndergroundSystem) GetAverageTime(startStation string, endStation string) float64 {
    v := this.avg[[2]string{startStation, endStation}]
    return float64(v[0]) / float64(v[1])
}


/**
 * Your UndergroundSystem object will be instantiated and called as such:
 * obj := Constructor();
 * obj.CheckIn(id,stationName,t);
 * obj.CheckOut(id,stationName,t);
 * param_3 := obj.GetAverageTime(startStation,endStation);
 */

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