private DLinkedNode PopTail()
{
DLinkedNode res = tail.Prev;
RemoveNode(res);
return(res);
}
public void Put(int key, int value)
{
DLinkedNode node = cache.ContainsKey(key) ? cache[key] : null;
if (node == null)
{
var newNode = new DLinkedNode
{
Key = key,
Value = value
};
cache.Add(key, newNode);
AddNode(newNode);
++size;
if (size <= capacity)
{
return;
}
// pop the tail
var popTail = PopTail();
cache.Remove(popTail.Key);
--size;
}
else
{
// update the value.
node.Value = value;
MoveToHead(node);
}
}
private static void RemoveNode(DLinkedNode node)
{
DLinkedNode prev = node.Prev;
DLinkedNode next = node.Next;
prev.Next = next;
next.Prev = prev;
}
private void AddNode(DLinkedNode node)
{
// add new one, next to head
node.Prev = head;
node.Next = head.Next;
head.Next.Prev = node;
head.Next = node;
}
public int Get(int key)
{
DLinkedNode node = cache[key];
if (node == null)
{
return(-1);
}
// move the accessed node to the head;
MoveToHead(node);
return(node.Value);
}
public LRUCache(int capacity)
{
this.size = 0;
this.capacity = capacity;
head = new DLinkedNode();
// head.prev = null;
tail = new DLinkedNode();
// tail.next = null;
head.Next = tail;
tail.Prev = head;
}
private void MoveToHead(DLinkedNode node)
{
RemoveNode(node);
AddNode(node);
}