删除Map()中最旧的条目，时间复杂度为O(1) JS

class LRUCache {
  constructor(capacity) {
    this.capacity = capacity;
    this.map = new Map();
    this.head = null;
    this.tail = null;
  }

  get(key) {
    if (this.map.has(key)) {
      const node = this.map.get(key);
      this.moveToHead(node);
      return node.value;
    }
    return -1;
  }

  put(key, value) {
    if (this.map.has(key)) {
      const node = this.map.get(key);
      node.value = value;
      this.moveToHead(node);
    } else {
      const newNode = { key, value, prev: null, next: null };
      if (this.map.size >= this.capacity) {
        this.removeTail();
      }
      this.addToHead(newNode);
      this.map.set(key, newNode);
    }
  }

  moveToHead(node) {
    if (node === this.head) {
      return;
    }
    if (node.prev) {
      node.prev.next = node.next;
    }
    if (node.next) {
      node.next.prev = node.prev;
    }
    if (node === this.tail) {
      this.tail = node.prev;
    }
    node.prev = null;
    node.next = this.head;
    if (this.head) {
      this.head.prev = node;
    }
    this.head = node;
  }

  removeTail() {
    if (!this.tail) {
      return;
    }
    this.map.delete(this.tail.key);
    if (this.tail.prev) {
      this.tail.prev.next = null;
    } else {
      this.head = null;
    }
    this.tail = this.tail.prev;
  }

  addToHead(node) {
    node.next = this.head;
    if (this.head) {
      this.head.prev = node;
    }
    this.head = node;
    if (!this.tail) {
      this.tail = node;
    }
  }
}

const cache = new LRUCache(5);
cache.put("key1", "value1");
cache.put("key2", "value2");
cache.put("key3", "value3");
cache.put("key4", "value4");
cache.put("key5", "value5");

console.log(cache.get("key3")); // 输出：value3
console.log(cache.get("key1")); // 输出：value1

cache.put("key6", "value6"); // 删除最旧的条目

console.log(cache.get("key2")); // 输出：-1，已被删除
console.log(cache.get("key6")); // 输出：value6