# 2622. Cache With Time Limit

## Description

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.

Example 1:

Input:
["TimeLimitedCache", "set", "get", "count", "get"]
[[], [1, 42, 100], , [], ]
[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], , , , []]
[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 <= 109
• 0 <= value <= 109
• 0 <= duration <= 1000
• total method calls will not exceed 100

## Solutions

• class TimeLimitedCache {
private cache: Map<number, [value: number, expire: number]> = new Map();

constructor() {}

set(key: number, value: number, duration: number): boolean {
this.removeExpire();
const ans = this.cache.has(key);
this.cache.set(key, [value, this.now() + duration]);
return ans;
}

get(key: number): number {
this.removeExpire();
return this.cache.get(key)?. ?? -1;
}

count(): number {
this.removeExpire();
return this.cache.size;
}

private now(): number {
return new Date().getTime();
}

private removeExpire(): void {
const now = this.now();
for (const [key, [, expire]] of this.cache) {
if (expire <= now) {
this.cache.delete(key);
}
}
}
}

/**
* Your TimeLimitedCache object will be instantiated and called as such:
* var obj = new TimeLimitedCache()
* obj.set(1, 42, 1000); // false
* obj.get(1) // 42
* obj.count() // 1
*/