Coding

2622. Cache With Time Limit

2023-05-18 3 min read
#Javascript#Typescript
On this page

⭐⭐⭐⭐

題目敘述

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.

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.

解題思路

Solution

var TimeLimitedCache = function() {
    this.cache = new Map();
};

/** 
 * @param {number} key
 * @param {number} value
 * @param {number} time until expiration in ms
 * @return {boolean} if un-expired key already existed
 */
TimeLimitedCache.prototype.set = function(key, value, duration) {
    const val = this.cache.get(key);
    if(val){
        clearTimeout(val.timeout);
    }

    const timeout = setTimeout(() => this.cache.delete(key), duration);
    this.cache.set(key, {value, timeout});
    return Boolean(val);
};

/** 
 * @param {number} key
 * @return {number} value associated with key
 */
TimeLimitedCache.prototype.get = function(key) {
    return this.cache.has(key) ? this.cache.get(key).value : -1;
};

/** 
 * @return {number} count of non-expired keys
 */
TimeLimitedCache.prototype.count = function() {
    return this.cache.size;
};

/**
 * 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
 */

class TimeLimitedCache {
    cache: Map<any, any>;

    constructor() {
        this.cache = new Map();
    }

    set(key: number, value: number, duration: number): boolean {
        const val: any = this.cache.get(key);
        if (val) {
            clearTimeout(val.timeout);
        }

        const timeout = setTimeout((): Boolean => this.cache.delete(key), duration);
        this.cache.set(key, { value, timeout });
        return Boolean(val);
    }

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

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

/**
 * 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
 */
← Posts
meow~