Implement the class UndergroundSystem
that supports three methods:
1. checkIn(int id, string stationName, int t)
- A customer with id card equal to
id
, gets in the stationstationName
at timet
. - A customer can only be checked into one place at a time.
2. checkOut(int id, string stationName, int t)
- A customer with id card equal to
id
, gets out from the stationstationName
at timet
.
3. getAverageTime(string startStation, string endStation)
- Returns the average time to travel between the
startStation
and theendStation
. - The average time is computed from all the previous traveling from
startStation
toendStation
that happened directly. - Call to
getAverageTime
is always valid.
You can assume all calls to checkIn
and checkOut
methods are consistent. That is, if a customer gets in at time t1 at some station, then it gets out at time t2 with t2 > t1. 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); undergroundSystem.checkOut(27, "Waterloo", 20); undergroundSystem.checkOut(32, "Cambridge", 22); undergroundSystem.getAverageTime("Paradise", "Cambridge"); // return 14.00000. There was only one travel from "Paradise" (at time 8) to "Cambridge" (at time 22) undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000. There were two travels from "Leyton" to "Waterloo", a customer with id=45 from time=3 to time=15 and a customer with id=27 from time=10 to time=20. So the average time is ( (15-3) + (20-10) ) / 2 = 11.00000 undergroundSystem.checkIn(10, "Leyton", 24); undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000 undergroundSystem.checkOut(10, "Waterloo", 38); undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 12.00000
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); undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.00000 undergroundSystem.checkIn(5, "Leyton", 10); undergroundSystem.checkOut(5, "Paradise", 16); undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.50000 undergroundSystem.checkIn(2, "Leyton", 21); undergroundSystem.checkOut(2, "Paradise", 30); undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 6.66667
Constraints:
- There will be at most
20000
operations. 1 <= id, t <= 10^6
- All strings consist of uppercase, lowercase English letters and digits.
1 <= stationName.length <= 10
- Answers within
10^-5
of the actual value will be accepted as correct.
class UndergroundSystem { HashMap<String, Pair<Integer, Integer>> checkoutMap = new HashMap<>(); // Route - {TotalTime, Count} HashMap<Integer, Pair<String, Integer>> checkInMap = new HashMap<>(); // Uid - {StationName, Time} public UndergroundSystem() {} public void checkIn(int id, String stationName, int t) { checkInMap.put(id, new Pair<>(stationName, t)); } public void checkOut(int id, String stationName, int t) { Pair<String, Integer> checkIn = checkInMap.get(id); String route = checkIn.getKey() + "_" + stationName; int totalTime = t - checkIn.getValue(); Pair<Integer, Integer> checkout = checkoutMap.getOrDefault(route, new Pair<>(0, 0)); checkoutMap.put(route, new Pair<>(checkout.getKey() + totalTime, checkout.getValue() + 1)); } public double getAverageTime(String startStation, String endStation) { String route = startStation + "_" + endStation; Pair<Integer, Integer> checkout = checkoutMap.get(route); return (double) checkout.getKey() / checkout.getValue(); } }