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1396. Design Underground System

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 station stationName at time t.
  • A customer can only be checked into one place at a time.
  1. checkOut(int id, string stationName, int t)
  • A customer with id card equal to id, gets out from the station stationName at time t.
  1. 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. 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.

Solutions (Rust)

1. HashMap

use std::collections::HashMap;

struct UndergroundSystem {
    still_in: HashMap<i32, (String, i32)>,
    times: HashMap<(String, String), (i32, i32)>,
}


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl UndergroundSystem {

    fn new() -> Self {
        Self {
            still_in: HashMap::new(),
            times: HashMap::new(),
        }
    }

    fn check_in(&mut self, id: i32, station_name: String, t: i32) {
        self.still_in.insert(id, (station_name, t));
    }

    fn check_out(&mut self, id: i32, station_name: String, t: i32) {
        let (start_name, start_t) = self.still_in.remove(&id).unwrap();
        let (time, cnt) = self.times.entry((start_name, station_name)).or_insert((0, 0));
        *time += t - start_t;
        *cnt += 1;
    }

    fn get_average_time(&self, start_station: String, end_station: String) -> f64 {
        let (time, cnt) = self.times.get(&(start_station, end_station)).unwrap();
        *time as f64 / *cnt as f64
    }
}

/**
 * Your UndergroundSystem object will be instantiated and called as such:
 * let obj = UndergroundSystem::new();
 * obj.check_in(id, stationName, t);
 * obj.check_out(id, stationName, t);
 * let ret_3: f64 = obj.get_average_time(startStation, endStation);
 */