1396. Design Underground System - Medium

前往題目

想法

• 用OOP解

思路

1. 乘客class，紀錄checkin和checkout時間地點
2. 路線class, 紀錄起站終站以及總共花費時間和次數
3. 用Map把id和乘客連接起來，路線和路線class連接起來

checkin:把乘客資訊加入即可

checkout:把乘客checkout，更新或加入路徑，最後移除乘客資訊，因為checkout了

average:直接找到該路徑，然後調用路徑class的average就可以算出來

Code

留言區解答

class UndergroundSystem {
    class Passenger {
        int checkInTime;
        int checkOutTime;
        String checkInStation;
        String checkOutStation;

        public Passenger(String checkInStation, int checkInTime) {
            this.checkInStation = checkInStation;
            this.checkInTime = checkInTime;
        }

        public void checkOut(String checkOutStation, int checkOutTime) {
            this.checkOutStation = checkOutStation;
            this.checkOutTime = checkOutTime;
        }
    }

    class Route {
        String startStation;
        String endStation;
        int totalTrips;
        long totalTimeSpentInTrips;

        public Route(String startStation, String endStation) {
            this.startStation = startStation;
            this.endStation = endStation;
        }

        public void addTrip(int startTime, int endTime) {
            totalTimeSpentInTrips += endTime - startTime;
            totalTrips += 1;
        }

        public double getAverage() {
            return (double) totalTimeSpentInTrips / totalTrips;
        }
    }

    Map<Integer, Passenger> passengerMap;
    Map<String, Route> routeMap;

    public UndergroundSystem() {
        passengerMap = new HashMap<>();
        routeMap = new HashMap<>();
    }
    
    public void checkIn(int id, String stationName, int t) {
        if (!passengerMap.containsKey(id)) {
            // CheckIn
            passengerMap.put(id, new Passenger(stationName, t));
        }
    }
    
    public void checkOut(int id, String stationName, int t) {
        if (passengerMap.containsKey(id)) {
            // Check out
            Passenger p = passengerMap.get(id);
            p.checkOut(stationName, t);
            
            // Adding or update route
            String routeKey = p.checkInStation + "," + p.checkOutStation;
            Route route = routeMap.getOrDefault(routeKey, new Route(p.checkInStation, p.checkOutStation));
            route.addTrip(p.checkInTime, p.checkOutTime);

            // Update route
            routeMap.put(routeKey, route);
            
            // Remove the passenger since checkout already
            passengerMap.remove(id);
        }
    }
    
    public double getAverageTime(String startStation, String endStation) {
        return routeMap.get(startStation + "," + endStation).getAverage();
    }
}