2622-CacheWithTimeLimit.js

// 2622. Cache With Time Limit
// 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 <= 10^9
//         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

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

/** 
 * @param {number} key
 * @param {number} value
 * @param {number} duration time until expiration in ms
 * @return {boolean} if un-expired key already existed
 */
TimeLimitedCache.prototype.set = function(key, value, duration) {
    const valueInCache = this.cache.get(key);
    // 如果该键已经存在，则它的值和持续时间都应该被覆盖。
    if (valueInCache) {
      clearTimeout(valueInCache.timeout);
    }
    // 添加一个删除的定时任务
    const timeout = setTimeout(() => this.cache.delete(key), duration);
    // { "value":"值","timeout":"定时器"}
    this.cache.set(key, { value, timeout });
    return Boolean(valueInCache);
};

/** 
 * @param {number} key
 * @return {number} value associated with key
 */
TimeLimitedCache.prototype.get = function(key) {
    // 如果存在一个未过期的键，它应该返回这个键相关的值。否则返回 -1
    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;
};

/**
 * const timeLimitedCache = new TimeLimitedCache()
 * timeLimitedCache.set(1, 42, 1000); // false
 * timeLimitedCache.get(1) // 42
 * timeLimitedCache.count() // 1
 */

const timeLimitedCache = new TimeLimitedCache()
timeLimitedCache.set(1, 42, 1000); // false
timeLimitedCache.get(1) // 42
timeLimitedCache.count() // 1