comments | difficulty | edit_url | tags | |
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true |
Medium |
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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: actions = ["TimeLimitedCache", "set", "get", "count", "get"] values = [[], [1, 42, 100], [1], [], [1]] timeDelays = [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: actions = ["TimeLimitedCache", "set", "set", "get", "get", "get", "count"] values = [[], [1, 42, 50], [1, 50, 100], [1], [1], [1], []] timeDelays = [0, 0, 40, 50, 120, 200, 250] Output: [null, false, true, 50, 50, -1, 0] 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, value <= 109
0 <= duration <= 1000
1 <= actions.length <= 100
actions.length === values.length
actions.length === timeDelays.length
0 <= timeDelays[i] <= 1450
actions[i]
is one of "TimeLimitedCache", "set", "get" and "count"- First action is always "TimeLimitedCache" and must be executed immediately, with a 0-millisecond delay
class TimeLimitedCache {
#cache: Map<number, [value: number, expire: number]> = new Map();
set(key: number, value: number, duration: number): boolean {
const isExist = this.#cache.has(key);
if (!this.#isExpired(key)) {
this.#cache.set(key, [value, Date.now() + duration]);
}
return isExist;
}
get(key: number): number {
if (this.#isExpired(key)) return -1;
const res = this.#cache.get(key)?.[0] ?? -1;
return res;
}
count(): number {
const xs = Array.from(this.#cache).filter(([key]) => !this.#isExpired(key));
return xs.length;
}
#isExpired = (key: number) =>
this.#cache.has(key) &&
(this.#cache.get(key)?.[1] ?? Number.NEGATIVE_INFINITY) < Date.now();
}
/**
* 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
*/