LRUCache.js

/**
 * @param {number} capacity
 */
const LRUCache = function (capacity) {
  this.capacity = capacity
  this.map = new Map()
}

/**
 * @param {number} key
 * @return {number}
 */
LRUCache.prototype.get = function (key) {
  if (!this.map.has(key)) {
    return -1
  }

  const value = this.map.get(key)
  this.map.delete(key)
  this.map.set(key, value)
  return value
}

/**
 * @param {number} key
 * @param {number} value
 * @return {void}
 */
LRUCache.prototype.put = function (key, value) {
  if (this.map.has(key)) {
    this.map.delete(key)
    this.map.set(key, value)
    return
  }

  if (this.map.size >= this.capacity) {
    const deleteKey = this.map.keys().next().value
    this.map.delete(deleteKey)
  }

  this.map.set(key, value)
}

/**
 * Your LRUCache object will be instantiated and called as such:
 * var obj = new LRUCache(capacity)
 * var param_1 = obj.get(key)
 * obj.put(key,value)
 */

module.exports = LRUCache