leetcode-设计地铁系统

 题目是LeetCode第182场周赛的第三题，链接：设计地铁系统。具体描述见原题链接。

 这道题其实偏向于数据结构的设计，这里直接用map来保存行程信息，主要是{乘客id–>入站名与入站时间}，{出站名–>{入站名–>总时长与总人次}}。这么做的好处在于可以将各种操作的时间复杂度都控制在 $O(1)$。

 JAVA版代码如下：

class UndergroundSystem {
    private Map<String, Map<String, int[]>> end2in;
    private Map<Integer, StationAndTime> inST;

    public UndergroundSystem() {
        end2in = new HashMap<>();
        inST = new HashMap<>();
    }
    
    public void checkIn(int id, String stationName, int t) {
        inST.put(id, new StationAndTime(stationName, t));
    }
    
    public void checkOut(int id, String stationName, int t) {
        StationAndTime in = inST.get(id);
        String in_station = in.getStation();
        int in_time = in.getTime();
        Map<String, int[]> inTimeCount = end2in.getOrDefault(stationName, new HashMap<>());
        int[] stationTime = inTimeCount.getOrDefault(in_station, new int[] {0, 0});
        stationTime[0] += t - in_time;
        ++stationTime[1];
        inTimeCount.put(in_station, stationTime);
        end2in.put(stationName, inTimeCount);
    }
    
    public double getAverageTime(String startStation, String endStation) {
        int[] timeAndCount = (end2in.get(endStation)).get(startStation);
        return timeAndCount[0] * 1.0 / timeAndCount[1];
    }
}

class StationAndTime {
    private String station;
    private int time;
    public StationAndTime(String name, int time) {
        this.station = name;
        this.time = time;
    }
    public String getStation() {
        return this.station;
    }
    public int getTime() {
        return this.time;
    }
}

/**
 * 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);
 */

 提交结果如下:

 Python版代码如下：

class UndergroundSystem:

    def __init__(self):
        # {出站名 : {入站名 : [总时间, 总人次]}}
        self.end2in = {}
        # {id : [入站名, 入站时间]}
        self.inST = {}

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

    def checkOut(self, id: int, stationName: str, t: int) -> None:
        in_station = (self.inST[id])[0]
        in_time = (self.inST[id])[1]
        # 更新一条路线的总时长与总人次
        if stationName in self.end2in:
            timeCount = (self.end2in[stationName])[in_station] if in_station in self.end2in[stationName] else [0, 0]
            timeCount[0] += t - in_time
            timeCount[1] += 1
            (self.end2in[stationName])[in_station] = timeCount
        else:
            self.end2in[stationName] = {in_station : [t - in_time, 1]}

    def getAverageTime(self, startStation: str, endStation: str) -> float:
        timeCount = (self.end2in[endStation])[startStation]
        return timeCount[0] / timeCount[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)

 提交结果如下: