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# Design Underground System

Updated: Mar 24, 2021

Implement the UndergroundSystem class:

• void checkIn(int id, string stationName, int t)

• A customer with a card id equal to id, gets in 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, gets out from the station stationName at time t.

• double getAverageTime(string startStation, string endStation)

• Returns the average time to travel between the startStation and the endStation.

• The average time is computed from all the previous traveling from startStation to endStation that happened directly.

• Call to getAverageTime is always valid.

You can assume all calls to checkIn and checkOut methods are consistent. If a customer gets in at time t1 at some station, they get 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"]

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(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"]

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.checkIn(5, "Leyton", 10);
undergroundSystem.checkIn(2, "Leyton", 21);
```

Constraints:

• There will be at most 20000 operations.

• 1 <= id, t <= 106

• All strings consist of uppercase and lowercase English letters, and digits.

• 1 <= stationName.length <= 10

• Answers within 10-5 of the actual value will be accepted as correct.

Solution:

```
class Trip{
String instation, outstation;
int intime, outtime;
public Trip(String station,int in)
{
this.instation = station;
this.intime = in;
}

}

class UndergroundSystem {

Map<Integer,Trip> customer;
Map<String,int[]> duration;

public UndergroundSystem()
{
customer = new HashMap<Integer,Trip>();
duration = new HashMap<String,int[]>();

}

public void checkIn(int id, String stationName, int t) {
customer.put(id,new Trip(stationName,t));

}

public void checkOut(int id, String stationName, int t) {
Trip tri = customer.get(id);
tri.outstation = stationName;
tri.outtime=t;

String key = tri.instation+"-"+tri.outstation;
if(duration.containsKey(key))
{
int[] temp = duration.get(key);
temp[0]+=(tri.outtime-tri.intime);
++temp[1];
}
else
{
duration.put(key,new int[]{tri.outtime-tri.intime,1});
}

}

public double getAverageTime(String startStation, String endStation) {
int[] tem = duration.get(startStation+"-"+endStation);
return (double)tem[0]/(double)tem[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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