【Q249】使用 js 实现一个 lru cache

[mrrs878]

可以借助Map实现

class LRUCache {
  constructor(limit) {
    this.limit = limit;
    this.cache = new Map();
  }

  get(key) {
    if (!this.cache.has(key)) return undefined;
    const value = this.cache.get(key);
    this.cache.delete(key);
    this.cache.set(key, value);
    return value;
  }

  put(key, value) {
    if (this.cache.has(key)) this.cache.delete(key);
    else if (this.cache.size >= this.limit) {
      this.cache.delete(this.cache.keys().next().value);
    }
    this.cache.set(key, value);
  }
}

// ["LRUCache","put","put","get","put","get","put","get","get","get"]
// [[2],[1,1],[2,2],[1],[3,3],[2],[4,4],[1],[3],[4]]
const lruCache = new LRUCache(2);
lruCache.put(1, 1);
lruCache.put(2, 2);
const res1 = lruCache.get(1);
lruCache.put(3, 3);
const res2 = lruCache.get(2);
lruCache.put(4, 4);
const res3 = lruCache.get(1);
const res4 = lruCache.get(3);
const res5 = lruCache.get(4);

console.log(res1, res2, res3, res4, res5);
// 1 undefined undefined 3 4

[haotie1990]

LRU (最近最少使用) 缓存机制

• 使用Map做数据保存
• 自建双向链表做元素使用频率保存及空间大小控制

[4may-mcx]

数组存key + map

class LRUCache {
  _stack = [];
  _map = {};

  constructor(len = 10) {
    this._len = len;
  }

  put(key, value) {
    if (this._stack.includes(key)) {
      this.update(key, value);
      return;
    }
    // 如果超过缓存的大小，那就删除数组中的最后一个值
    if (this._stack.length >= this._len) {
      const delKey = this._stack[this._len - 1];
      this.delete(delKey);
    }
    this.set(key, value);
  }

  set(key, value) {
    this._stack.unshift(key);
    this._map[key] = value;
  }

  get(key) {
    if (this._map[key]) {
      this.update(key);
      return this._map[key];
    }
    return -1;
  }

  update(key, value) {
    const index = this._stack.indexOf(key);
    this._stack.splice(index, 1);
    this._stack.unshift(key);
    if (value) {
      this._map[key] = value;
    }
  }

  delete(key) {
    delete this._map[key];
    this._stack.pop();
  }
}

export default LRUCache;

[iamphc]

function Node(key, val){
  this.prev=null
  this.next=null
  this.key=key
  this.val=val
}
function DoubleList(){
  this._node=new Node(null, null)
  this.size=0
  // 插入到头部
  this.addFirst=(node)=>{
    // 找到头节点
    while(this._node){
      this._node=this._node.prev
    }
    // 处理头节点
    this._node.prev=node
    node.next=this._node
    // 找到尾节点
    while(this._node){
      this._node=this._node.next
    }
    // 处理尾节点
    this._node.prev.next=null
    this._node.prev=null
    this.size++
  }
  // 移除一个节点
  this.remove=(node)=>{
    if(!this.size) return -1
    const prev=node.prev
    const next=node.next
    if(prev) {
      node.prev.next=node.next
    }
    if(next){
      node.next.prev=node.prev
    }
    this.size--
  }
  // 移除最后一个节点，并返回该节点
  this.removeLast=()=>{
    if(!this.size) return -1
    while(this._node){
      this._node=this._node.next
    }
    this.remove(this._node)
    return this._node
  }
}
function LRUcache(limit) {
  this._limit=limit
  this._doubleList=new DoubleList()
  this._map=new Map()
  // 获取key对应的节点，并将节点提前
  this.get=(key)=>{
    if(!this._map.has(key)) return -1
    const node=this._map.get(key)
    this._doubleList.addFirst(node)
    return node
  }
  // 插入节点，并将节点提前
  this.put=(key, val)=>{
    const node=new Node(key,val)
    if(this._map.has(key)){
      this._doubleList.remove(this._map.get(key))
    }
    if(this._doubleList.size===this._limit){
      const lastNode=this._doubleList.removeLast()
      this._map.delete(lastNode.key)
    }
    this._doubleList.addFirst(node)
    this._map.set(key,node)
  }
}