/// <summary>
/// 插入元素到头部
/// <para/>
/// * 默认为节点没有添加到列表，并且待添加的节点 <see cref="LRUSpecializedLinkedListNode{TValue}.Previous"/> 和 <see cref="LRUSpecializedLinkedListNode{TValue}.Next"/> 都为 null
/// </summary>
/// <param name="node"></param>
/// <returns></returns>
public LRUSpecializedLinkedListNode <TValue>?InsertAtHead(LRUSpecializedLinkedListNode <TValue> node)
{
if (_count > 1)
{
_head !.Previous = node;
node.Next = _head;
_head = node;
if (_count >= _capacity)
{
return(RemoveTail());
}
_count++;
}
else if (_count == 1)
{
_count = 2;
_tail = _head;
_head = node;
_head.Next = _tail;
_tail !.Previous = _head;
}
else
{
_count = 1;
_head = node;
}
return(null);
}
/// <summary>
/// 移除节点
/// <para/>
/// * 默认为节点已经通过 <see cref="InsertAtHead(LRUSpecializedLinkedListNode{TValue})"/> 添加到列表
/// </summary>
/// <param name="node"></param>
public void Remove(LRUSpecializedLinkedListNode <TValue> node)
{
if (node.Previous is not null) //移除的不是首节点
{
node.Previous.Next = node.Next;
if (node.Next is not null) //移除的不是尾节点
{
node.Next.Previous = node.Previous;
}
else //移除的是尾节点
{
_tail = node.Previous;
_tail.Next = null;
}
}
else //移除的是首节点
{
_head = node.Next;
if (_head is not null)
{
_head.Previous = null;
}
}
if (--_count == 1)
{
_tail = null;
}
}
/// <summary>
/// 移动元素到头部
/// <para/>
/// * 默认为节点已经通过 <see cref="InsertAtHead(LRUSpecializedLinkedListNode{TValue})"/> 添加到列表
/// </summary>
/// <param name="node"></param>
public void MoveToHead(LRUSpecializedLinkedListNode <TValue> node)
{
if (node == _head)
{
return;
}
if (node == _tail)
{
_tail = _tail.Previous;
_tail !.Next = null;
_head !.Previous = node;
node.Next = _head;
node.Previous = null;
_head = node;
return;
}
node.Previous !.Next = node.Next;
node.Next !.Previous = node.Previous;
_head !.Previous = node;
node.Next = _head;
node.Previous = null;
_head = node;
}
private LRUSpecializedLinkedListNode <TValue>?RemoveTail()
{
var removedNode = _tail;
_tail = _tail !.Previous;
_tail !.Next = null;
return(removedNode);
}