type Node struct {
  Key int
  Value int
  pre *Node
  next *Node
}

type LRUCache struct {
  limit int
  HashMap map[int]*Node
  head *Node
  end *Node
}

func Constructor(capacity int) LRUCache{
  lruCache := LRUCache{limit:capacity}
  lruCache.HashMap = make(map[int]*Node, capacity)
  return lruCache
}

func (l *LRUCache) Get(key int) int {
  if v,ok:= l.HashMap[key];ok {
    l.refreshNode(v)
    return v.Value
  }else {
    return -1
  }
}

func (l *LRUCache) Put(key int, value int) {
  if v,ok := l.HashMap[key];!ok{
    if len(l.HashMap) >= l.limit{
      oldKey := l.removeNode(l.head)
      delete(l.HashMap, oldKey)
    }
    node := Node{Key:key, Value:value}
    l.addNode(&node)
    l.HashMap[key] = &node
  }else {
    v.Value = value
    l.refreshNode(v)
  }
}

func (l *LRUCache) refreshNode(node *Node){
  if node == l.end {
    return
  }
  l.removeNode(node)
  l.addNode(node)
}

func (l *LRUCache) removeNode(node *Node) int{
  if node == l.end {
    l.end = l.end.pre
  }else if node == l.head {
    l.head = l.head.next
  }else {
    node.pre.next = node.next
    node.next.pre = node.pre
  }
  return node.Key
}

func (l *LRUCache) addNode(node *Node){
  if l.end != nil {
    l.end.next = node
    node.pre = l.end
    node.next = nil
  }
  l.end = node
  if l.head == nil {
    l.head = node
  }
}