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1396. 设计地铁系统

English Version

题目描述

请你实现一个类 UndergroundSystem ，它支持以下 3 种方法：

1. checkIn(int id, string stationName, int t)

  • 编号为 id 的乘客在 t 时刻进入地铁站 stationName 。
  • 一个乘客在同一时间只能在一个地铁站进入或者离开。

2. checkOut(int id, string stationName, int t)

  • 编号为 id 的乘客在 t 时刻离开地铁站 stationName 。

3. getAverageTime(string startStation, string endStation) 

  • 返回从地铁站 startStation 到地铁站 endStation 的平均花费时间。
  • 平均时间计算的行程包括当前为止所有从 startStation 直接到达 endStation 的行程。
  • 调用 getAverageTime 时，询问的路线至少包含一趟行程。

你可以假设所有对 checkIn 和 checkOut 的调用都是符合逻辑的。也就是说，如果一个顾客在 t1 时刻到达某个地铁站，那么他离开的时间 t2 一定满足 t2 > t1 。所有的事件都按时间顺序给出。

 

示例：

输入：
["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"]]

输出：
[null,null,null,null,null,null,null,14.0,11.0,null,11.0,null,12.0]

解释：
UndergroundSystem undergroundSystem = new UndergroundSystem();
undergroundSystem.checkIn(45, "Leyton", 3);
undergroundSystem.checkIn(32, "Paradise", 8);
undergroundSystem.checkIn(27, "Leyton", 10);
undergroundSystem.checkOut(45, "Waterloo", 15);
undergroundSystem.checkOut(27, "Waterloo", 20);
undergroundSystem.checkOut(32, "Cambridge", 22);
undergroundSystem.getAverageTime("Paradise", "Cambridge");       // 返回 14.0。从 "Paradise"（时刻 8）到 "Cambridge"(时刻 22)的行程只有一趟
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // 返回 11.0。总共有 2 躺从 "Leyton" 到 "Waterloo" 的行程，编号为 id=45 的乘客出发于 time=3 到达于 time=15，编号为 id=27 的乘客于 time=10 出发于 time=20 到达。所以平均时间为 ( (15-3) + (20-10) ) / 2 = 11.0
undergroundSystem.checkIn(10, "Leyton", 24);
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // 返回 11.0
undergroundSystem.checkOut(10, "Waterloo", 38);
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // 返回 12.0

 

提示：

  • 总共最多有 20000 次操作。
  • 1 <= id, t <= 10^6
  • 所有的字符串包含大写字母，小写字母和数字。
  • 1 <= stationName.length <= 10
  • 与标准答案误差在 10^-5 以内的结果都视为正确结果。

解法

“哈希表”实现。

Python3

class UndergroundSystem:

    def __init__(self):
        self.check_in_station = {}
        self.check_in_time = {}
        self.total_time = {}

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

    def checkOut(self, id: int, stationName: str, t: int) -> None:
        cost = t - self.check_in_time.pop(id)
        start_station = self.check_in_station.pop(id)
        stations = start_station + '.' + stationName
        times = self.total_time.get(stations, [0, 0])
        times[0] += cost
        times[1] += 1
        self.total_time[stations] = times

    def getAverageTime(self, startStation: str, endStation: str) -> float:
        stations = startStation + '.' + endStation
        times = self.total_time[stations]
        return times[0] / times[1]


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

Java

class UndergroundSystem {
    private Map<Integer, String> checkInStation;
    private Map<Integer, Integer> checkInTime;
    private Map<String, int[]> totalTime;

    public UndergroundSystem() {
        checkInStation = new HashMap<>();
        checkInTime = new HashMap<>();
        totalTime = new HashMap<>();
    }

    public void checkIn(int id, String stationName, int t) {
        checkInStation.put(id, stationName);
        checkInTime.put(id, t);
    }

    public void checkOut(int id, String stationName, int t) {
        int cost = t - checkInTime.remove(id);
        String startStation = checkInStation.remove(id);
        String stations = startStation + "." + stationName;
        int[] times = totalTime.getOrDefault(stations, new int[2]);
        times[0] += cost;
        ++times[1];
        totalTime.put(stations, times);
    }

    public double getAverageTime(String startStation, String endStation) {
        String stations = startStation + "." + endStation;
        int[] times = totalTime.get(stations);
        return times[0] * 1.0 / times[1];
    }
}

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

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