0146. LRU Cache.js

// Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and put.
//
// get(key) - Get the value (will always be positive) of the key if the key exists in the cache, otherwise return -1.
// put(key, value) - Set or insert the value if the key is not already present. When the cache reached its capacity, it should invalidate the least recently used item before inserting a new item.
//
// Follow up:
//
// Could you do both operations in O(1) time complexity?
//
// Example:
//
// LRUCache cache = new LRUCache( 2 /* capacity );
//
// cache.put(1, 1);
// cache.put(2, 2);
// cache.get(1);       // returns 1
// cache.put(3, 3);    // evicts key 2
// cache.get(2);       // returns -1 (not found)
// cache.put(4, 4);    // evicts key 1
// cache.get(1);       // returns -1 (not found)
// cache.get(3);       // returns 3
// cache.get(4);       // returns 4

class LRUCache {
  /**
   * @param {number} capacity
   */
  constructor(capacity) {
    this.cache = new Map();
    this.capacity = capacity;
  }

  /**
   * @param {number} key
   * @return {number}
   */
  get(key) {
    if (!this.cache.has(key)) return -1;
    const val = this.cache.get(key);
    this.cache.delete(key);
    this.cache.set(key, val);
    return this.cache.get(key);
  };

  /**
   * @param {number} key
   * @param {number} value
   * @return {void}
   */
  put(key, value) {
    if (this.cache.has(key)) {
      this.cache.delete(key);
    }
    this.cache.set(key, value);
    if (this.cache.size > this.capacity) {
      this.cache.delete(this.cache.keys().next().value); // keys().next().value returns the oldest / first key
    }
  };
}