ARTS #152

Algorithm

规则

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.

Solution

class UndergroundSystem:

    def __init__(self):
        self.checkIns = dict()
        self.routeTimes = defaultdict(int)
        self.routeCount = defaultdict(int)

    def checkIn(self, id: int, stationName: str, t: int) -> None:
        self.checkIns[id] = stationName, t

    def checkOut(self, id: int, stationName: str, t: int) -> None:
        startStation, startTime = self.checkIns.pop(id)

        routeName = startStation, stationName 
        self.routeTimes[routeName] += t - startTime
        self.routeCount[routeName] += 1

    def getAverageTime(self, startStation: str, endStation: str) -> float:
        routeName = startStation, endStation
        return self.routeTimes[routeName] / self.routeCount[routeName]

# Your UndergroundSystem object will be instantiated and called as such:
# obj = UndergroundSystem()
# obj.checkIn(id,stationName,t)
# obj.checkOut(id,stationName,t)
# param_3 = obj.getAverageTime(startStation,endStation)

Review

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有完整的缓存、跨域、鉴权、重定向管理策略
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能同时在客户端和服务端上使用，比如 Deno、Node 18

XMLHttpRequest 的优势：

可以通过 onprogress 实现进度追踪
支持超时设置
不像 Fetch 的 AbortController，可以轻易实现中断
对低版本浏览器（IE 或 2015 年以前的浏览器版本）的兼容性更好

Tip

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高性能 - Rust + Metal，纯 native 应用，由于 MacOS 是第一目标平台，选择了 Metal over OpenGL 作为 GPU API
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值得注意的是，他们会对用户数据进行分析 - 基于 telemetry

作为一款新产品，难免有 bug：

再继续使用看看~

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变化往往伴随着失去。如果总说改变，却依然驻足原地，恐怕是不知道变化会令人失去什么，而且大多数巨变都是靠我们用数百个微不足道、甚至难以察觉的一小步累积而来的，一步之中蕴含着许多可能性
安宁，不是要身处一个没有嘈杂、烦恼和辛劳的地方，而是即使身处于繁杂之中依然保持内心的平静
不言而喻的讽刺：人们想给自己的问题找到一个快速的解决方案，但殊不知一开始导致他们情绪问题的，就是生活中太过匆忙的节奏。他们以为现在的忙碌是为了以后能有机会享受生活，但往往，后来就没有“后来”了

五一期间打算看完跟老婆一起带孩子。

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