1396. Design Underground System (M)

Design Underground System (M)

题目

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.

2. checkOut(int id, string stationName, int t)

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

3.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,14.0,11.0,null,11.0,null,12.0]

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 14.0. There was only one travel from "Paradise" (at time 8) to "Cambridge" (at time 22)
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // return 11.0. 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 = 11.0
undergroundSystem.checkIn(10, "Leyton", 24);
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // return 11.0
undergroundSystem.checkOut(10, "Waterloo", 38);
undergroundSystem.getAverageTime("Leyton", "Waterloo");          // return 12.0

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.

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题意

实现一个地铁系统类的三个方法。

思路

使用两个HashMap处理：

1. 第一个map记录编号id的乘客的入站信息；
2. 第二个map记录线路'A-B'对应的行驶总用时和行驶次数。

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代码实现

Java

class UndergroundSystem {
    private Map<Integer, Object[]> start;
    private Map<String, int[]> route;

    public UndergroundSystem() {
        start = new HashMap<>();
        route = new HashMap<>();
    }

    public void checkIn(int id, String stationName, int t) {
        start.putIfAbsent(id, new Object[2]);
        Object[] list = start.get(id);
        list[0] = stationName;
        list[1] = t;
    }

    public void checkOut(int id, String stationName, int t) {
        Object[] info = start.get(id);
        String routeName = (String) info[0] + '-' + stationName;
        int prev = (int) info[1];
        
        route.putIfAbsent(routeName, new int[2]);
        int[] list = route.get(routeName);
        list[0] += t - prev;
        list[1]++;
    }

    public double getAverageTime(String startStation, String endStation) {
        String routeName = startStation + '-' + endStation;
        int[] list = route.get(routeName);
        
        return 1.0 * list[0] / list[1];
    }
}

JavaScript

var UndergroundSystem = function () {
  this.travel = new Map()
  this.record = new Map()
}

/**
 * @param {number} id
 * @param {string} stationName
 * @param {number} t
 * @return {void}
 */
UndergroundSystem.prototype.checkIn = function (id, stationName, t) {
  this.travel.set(id, [stationName, t])
}

/**
 * @param {number} id
 * @param {string} stationName
 * @param {number} t
 * @return {void}
 */
UndergroundSystem.prototype.checkOut = function (id, stationName, t) {
  const from = this.travel.get(id)[0]
  const to = stationName
  const interval = t - this.travel.get(id)[1]

  if (!this.record.has(from)) {
    this.record.set(from, new Map())
  }
  if (!this.record.get(from).has(to)) {
    this.record.get(from).set(to, [])
  }
  this.record.get(from).get(to).push(interval)

  this.travel.delete(id)
}

/**
 * @param {string} startStation
 * @param {string} endStation
 * @return {number}
 */
UndergroundSystem.prototype.getAverageTime = function (startStation, endStation) {
  const arr = this.record.get(startStation).get(endStation)
  return arr.reduce((acc, cur) => acc + cur) / arr.length
}