LeetCode: Design Underground System Solution

Approach

Init two hash tables

  • one stores the k-v pair of current check-in info of a customer
  • one stores the k-v pairs of route and its accumulated total time

Implementation

1var UndergroundSystem = function () {
2 this.checkInMap = new Map()
3 this.routeTotalTimeMap = new Map()
4}
5
6/**
7 * @param {number} id
8 * @param {string} stationName
9 * @param {number} t
10 * @return {void}
11 */
12UndergroundSystem.prototype.checkIn = function (id, stationName, t) {
13 this.checkInMap.set(id, { stationName, t })
14}
15
16/**
17 * @param {number} id
18 * @param {string} stationName
19 * @param {number} t
20 * @return {void}
21 */
22UndergroundSystem.prototype.checkOut = function (id, stationName, t) {
23 const route = `${this.checkInMap.get(id).stationName} - ${stationName}`
24 if (!this.routeTotalTimeMap.has(route)) {
25 this.routeTotalTimeMap.set(route, {
26 total: 0,
27 count: 0,
28 })
29 }
30 const routeTotalTime = this.routeTotalTimeMap.get(route)
31 this.routeTotalTimeMap.set(route, {
32 total: routeTotalTime.total + (t - this.checkInMap.get(id).t),
33 count: routeTotalTime.count + 1,
34 })
35 this.checkInMap.delete(id)
36}
37
38/**
39 * @param {string} startStation
40 * @param {string} endStation
41 * @return {number}
42 */
43UndergroundSystem.prototype.getAverageTime = function (
44 startStation,
45 endStation
46) {
47 const route = `${startStation} - ${endStation}`
48 const routeTotalTime = this.routeTotalTimeMap.get(route)
49 return routeTotalTime.total / routeTotalTime.count
50}
51
52/**
53 * Your UndergroundSystem object will be instantiated and called as such:
54 * var obj = new UndergroundSystem()
55 * obj.checkIn(id,stationName,t)
56 * obj.checkOut(id,stationName,t)
57 * var param_3 = obj.getAverageTime(startStation,endStation)
58 */

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leetcode

hash table

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