1396. Design Underground System

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"]
[[],[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 <= 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.

Rust Solution

use std::collections::HashMap;

#[derive(Default)]
struct UndergroundSystem {
    time: HashMap<String, HashMap<String, (i32, i32)>>,
    customer: HashMap<i32, (String, i32)>,
}

impl UndergroundSystem {
    fn new() -> Self {
        UndergroundSystem::default()
    }

    fn check_in(&mut self, id: i32, start_station: String, start_t: i32) {
        self.customer.insert(id, (start_station, start_t));
    }

    fn check_out(&mut self, id: i32, end_station: String, end_t: i32) {
        let (start_station, start_t) = self.customer.remove(&id).expect("in");
        let (sum, count) = self
            .time
            .entry(start_station)
            .or_default()
            .entry(end_station)
            .or_default();
        *sum += end_t - start_t;
        *count += 1;
    }

    fn get_average_time(&mut self, start_station: String, end_station: String) -> f64 {
        let (sum, count) = self
            .time
            .entry(start_station)
            .or_default()
            .entry(end_station)
            .or_default();
        *sum as f64 / *count as f64
    }
}

#[test]
fn test() {
    use assert_approx_eq::assert_approx_eq;
    let mut obj = UndergroundSystem::new();
    obj.check_in(45, "Leyton".to_string(), 3);
    obj.check_in(32, "Paradise".to_string(), 8);
    obj.check_in(27, "Leyton".to_string(), 10);
    obj.check_out(45, "Waterloo".to_string(), 15);
    obj.check_out(27, "Waterloo".to_string(), 20);
    obj.check_out(32, "Cambridge".to_string(), 22);
    let t = obj.get_average_time("Paradise".to_string(), "Cambridge".to_string());
    assert_approx_eq!(t, 14.0);
    let t = obj.get_average_time("Leyton".to_string(), "Waterloo".to_string());
    assert_approx_eq!(t, 11.0);
    obj.check_in(10, "Leyton".to_string(), 24);
    let t = obj.get_average_time("Leyton".to_string(), "Waterloo".to_string());
    assert_approx_eq!(t, 11.0);
    obj.check_out(10, "Waterloo".to_string(), 38);
    let t = obj.get_average_time("Leyton".to_string(), "Waterloo".to_string());
    assert_approx_eq!(t, 12.0);
}

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