Package g1301_1400.s1396_design_underground_system

Class UndergroundSystem

java.lang.Object
g1301_1400.s1396_design_underground_system.UndergroundSystem
public class UndergroundSystem extends java.lang.Object
1396 - Design Underground System.

Medium

An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another.

Implement the UndergroundSystem class:

  • void checkIn(int id, string stationName, int t)
    • A customer with a card ID equal to id, checks in at 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, checks out from the station stationName at time t.
  • double getAverageTime(string startStation, string endStation)
    • Returns the average time it takes to travel from startStation to endStation.
    • The average time is computed from all the previous traveling times from startStation to endStation that happened directly , meaning a check in at startStation followed by a check out from endStation.
    • The time it takes to travel from startStation to endStation may be different from the time it takes to travel from endStation to startStation.
    • There will be at least one customer that has traveled from startStation to endStation before getAverageTime is called.

You may assume all calls to the checkIn and checkOut methods are consistent. If a customer checks in at time t1 then checks out at time t2, then t1 < t2. 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); // Customer 45 "Leyton" -> "Waterloo" in 15-3 = 12
 undergroundSystem.checkOut(27, "Waterloo", 20); // Customer 27 "Leyton" -> "Waterloo" in 20-10 = 10
 undergroundSystem.checkOut(32, "Cambridge", 22); // Customer 32 "Paradise" -> "Cambridge" in 22-8 = 14
 undergroundSystem.getAverageTime("Paradise", "Cambridge"); // return 14.00000. One trip "Paradise" -> "Cambridge", (14) / 1 = 14
 undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000. Two trips "Leyton" -> "Waterloo", (10 + 12) / 2 = 11
 undergroundSystem.checkIn(10, "Leyton", 24);
 undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 11.00000
 undergroundSystem.checkOut(10, "Waterloo", 38); // Customer 10 "Leyton" -> "Waterloo" in 38-24 = 14
 undergroundSystem.getAverageTime("Leyton", "Waterloo"); // return 12.00000. Three trips "Leyton" -> "Waterloo", (10 + 12 + 14) / 3 = 12

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); // Customer 10 "Leyton" -> "Paradise" in 8-3 = 5
 undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.00000, (5) / 1 = 5
 undergroundSystem.checkIn(5, "Leyton", 10);
 undergroundSystem.checkOut(5, "Paradise", 16); // Customer 5 "Leyton" -> "Paradise" in 16-10 = 6
 undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 5.50000, (5 + 6) / 2 = 5.5
 undergroundSystem.checkIn(2, "Leyton", 21);
 undergroundSystem.checkOut(2, "Paradise", 30); // Customer 2 "Leyton" -> "Paradise" in 30-21 = 9
 undergroundSystem.getAverageTime("Leyton", "Paradise"); // return 6.66667, (5 + 6 + 9) / 3 = 6.66667

Constraints:

  • 1 <= id, t <= 106
  • 1 <= stationName.length, startStation.length, endStation.length <= 10
  • All strings consist of uppercase and lowercase English letters and digits.
  • There will be at most 2 * 104 calls in total to checkIn, checkOut, and getAverageTime.
  • Answers within 10-5 of the actual value will be accepted.

  • Constructor Summary

    Constructors
    Constructor
    Description
    UndergroundSystem()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    checkIn(int id, java.lang.String stationName, int t)
     
    void
    checkOut(int id, java.lang.String stationName, int t)
     
    double
    getAverageTime(java.lang.String startStation, java.lang.String endStation)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • UndergroundSystem

      public UndergroundSystem()

  • Method Details

    • checkIn

      public void checkIn(int id, java.lang.String stationName, int t)

    • checkOut

      public void checkOut(int id, java.lang.String stationName, int t)

    • getAverageTime

      public double getAverageTime(java.lang.String startStation, java.lang.String endStation)