Algorithm
30 Days of JavaScript
Cache with Time Limit

2622. Cache With Time Limit

Tags

  • Promises and Time

Link

https://leetcode.com/problems/cache-with-time-limit/description/?envType=study-plan-v2&envId=30-days-of-javascript (opens in a new tab)

Question

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 <= t <= 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

Answer

JavaScript

var TimeLimitedCache = function () {
  this.cache = new Map(); // Using Map so we don't need a size variable
};
 
/**
 * @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 expiration = () => {
    const timeoutId = setTimeout(() => this.cache.delete(key), duration); // new timeout for key expiration
    this.cache.set(key, { value, timeoutId }); // update cache with value & timeoutId
  };
 
  const activeKey = this.cache.has(key);
  if (activeKey) {
    // if unexpired key in cache alr
    clearTimeout(this.cache.get(key).timeoutId); // clear existing timeout
  }
  expiration();
  return activeKey;
 
  // const now = Date.now();
  // const expiresAt = now + duration;
  // const exists = this.cache.has(key) && this.cache.get(key).expiresAt > now;
  // this.cache.set(key, { value, expiresAt });
  // return exists;
 
  // let hasKey = this.cache.has(key);
  // if(hasKey){
  //     clearTimeout(this.cache.get(key).timeout)
  // }
  // const timeout = setTimeout(() => this.cache.delete(key), duration);
  // this.cache.set(key, {value, timeout})
  // return hasKey;
 
  // let found = this.cache.has(key);
  // if (found) clearTimeout(this.cache.get(key).ref);  // Cancel previous timeout
  // this.cache.set(key, {
  //     value,  // Equivalent to `value: value`
  //     ref: setTimeout(() => this.cache.delete(key), duration)
  // });
  // return found;
};
 
/**
 * @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;
};
 
/**
 * const timeLimitedCache = new TimeLimitedCache()
 * timeLimitedCache.set(1, 42, 1000); // false
 * timeLimitedCache.get(1) // 42
 * timeLimitedCache.count() // 1
 */
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