一句话：淘汰不活跃的值，如果都不活跃先淘汰前面的

class LRUCache {
  capacity: number // 容量
  cache: Map<any, any>
  order: any[]
  constructor(capacity: number) {
    this.capacity = capacity
    this.cache = new Map()
    this.order = []
  }
  get(key: any) {
    if (this.cache.has(key)) {
      const value = this.cache.get(key)
      this.updateOrder(key)
      return value
    } else {
      return null
    }
  }

  set(key: any, value: any) {
    if (this.cache.has(key)) {
      // 说明值存过了
      this.cache.set(key)
      this.updateOrder(key)
    } else {
      this.cache.set(key)
      this.order.push(key)
      // 如果超出容量
      if (this.order.length > this.capacity) {
        const oldKey = this.order.shift()
        this.cache.delete(oldKey)
      }
    }
  }

  updateOrder(key: any) {
    const index = this.order.indexOf(key)
    this.order.splice(index, 1)
    this.order.push(key)
  }
}
const lru = new LRUCache(3)