# 2622. Cache With Time Limit
###### tags: `leetcode 30 days js challenge` `Medium`
[2622. Cache With Time Limit](https://leetcode.com/problems/cache-with-time-limit/)
### 題目描述
Write a class that allows getting and setting key-value pairs, however a **time until expiration** is associated with each key.
The class has three public methods:
`set(key, value, duration)`: accepts an integer `key`, an integer `value`, and a `duration` in milliseconds. Once the `duration` has elapsed, the key should be inaccessible. The method should return `true` if the same un-expired key already exists and `false` otherwise. Both the value and duration should be overwritten if the key already exists.
`get(key)`: if an un-expired key exists, it should return the associated value. Otherwise it should return `-1`.
`count()`: returns the count of un-expired keys.
### 範例
**Example 1:**
```
Input:
["TimeLimitedCache", "set", "get", "count", "get"]
[[], [1, 42, 100], [1], [], [1]]
[0, 0, 50, 50, 150]
Output: [null, false, 42, 1, -1]
Explanation:
At t=0, the cache is constructed.
At t=0, a key-value pair (1: 42) is added with a time limit of 100ms. The value doesn't exist so false is returned.
At t=50, key=1 is requested and the value of 42 is returned.
At t=50, count() is called and there is one active key in the cache.
At t=100, key=1 expires.
At t=150, get(1) is called but -1 is returned because the cache is empty.
```
**Example 2:**
```
Input:
["TimeLimitedCache", "set", "set", "get", "get", "get", "count"]
[[], [1, 42, 50], [1, 50, 100], [1], [1], [1], []]
[0, 0, 40, 50, 120, 200, 250]
Output: [null, false, true, 50, 50, -1]
Explanation:
At t=0, the cache is constructed.
At t=0, a key-value pair (1: 42) is added with a time limit of 50ms. The value doesn't exist so false is returned.
At t=40, a key-value pair (1: 50) is added with a time limit of 100ms. A non-expired value already existed so true is returned and the old value was overwritten.
At t=50, get(1) is called which returned 50.
At t=120, get(1) is called which returned 50.
At t=140, key=1 expires.
At t=200, get(1) is called but the cache is empty so -1 is returned.
At t=250, count() returns 0 because the cache is empty.
```
**Constraints**:
- 0 <= key <= 10<sup>9</sup>
- 0 <= value <= 10<sup>9</sup>
- 0 <= duration <= 1000
- total method calls will not exceed 100
### 解答
#### TypeScript
```typescript=
class TimeLimitedCache {
private cache: {
[key: number]: {
value: number;
expiredTime: number;
};
};
constructor() {
this.cache = {};
}
set(key: number, value: number, duration: number): boolean {
const currentTime = Date.now();
const existed = this.cache[key] ? this.cache[key].expiredTime > currentTime : false;
this.cache[key] = {
value,
expiredTime: Date.now() + duration,
};
return existed;
}
get(key: number): number {
const currentTime = Date.now();
if (this.cache[key]?.expiredTime > currentTime) {
return this.cache[key].value;
}
return -1;
}
count(): number {
const currentTime = Date.now();
let counts = 0;
for (const value of Object.values(this.cache)) {
if (value.expiredTime - currentTime > 0) {
counts++;
}
}
return counts;
}
}
```
`setTimeout` + `clearTimeout` 寫法:
```typescript=
class TimeLimitedCache {
cache = new Map<number, { value: number; timeout: NodeJS.Timeout }>();
set(key: number, value: number, duration: number) {
const valueInCache = this.cache.get(key);
if (valueInCache) {
clearTimeout(valueInCache.timeout);
}
const timeout = setTimeout(() => this.cache.delete(key), duration);
this.cache.set(key, { value, timeout });
return Boolean(valueInCache);
}
get(key: number) {
return this.cache.has(key) ? this.cache.get(key)?.value : -1;
}
count() {
return this.cache.size;
}
}
```
Priority Queue
```typescript=
import { MinPriorityQueue } from '@datastructures-js/priority-queue';
type Entry = {
key: number;
value: number;
expiration: number;
overwritten: boolean;
};
class TimeLimitedCache {
cache: Record<string, Entry> = {};
queue = new MinPriorityQueue<Entry>();
size = 0;
handleExpiredData() {
const now = Date.now();
while (this.queue.size() > 0 && this.queue.front().expiration < now) {
const entry = this.queue.dequeue();
if (!entry.overwritten) {
delete this.cache[entry.key];
this.size -= 1;
}
}
}
set(key: number, value: number, duration: number) {
this.handleExpiredData();
const hasVal = key in this.cache;
if (hasVal) {
this.cache[key].overwritten = true;
} else {
this.size += 1;
}
const expiration = Date.now() + duration;
const entry: Entry = { key, value, expiration, overwritten: false };
this.cache[key] = entry;
this.queue.enqueue(entry);
return hasVal;
}
get(key: number) {
this.handleExpiredData();
if (this.cache[key] === undefined) return -1;
return this.cache[key].value;
}
count() {
this.handleExpiredData();
return this.size;
}
}
```
> [name=Sheep][time=Thur, May 18, 2023]
### Reference
[回到題目列表](https://hackmd.io/@Marsgoat/leetcode_every_day)