public void Clear()
{
this.Map = new Dictionary <string, LRUNode <T> >();
Head = null;
Tail = null;
CurrentSize = 0;
}
public LRUCache(int maxSize)
{
MaxSize = maxSize;
Head = null;
Tail = null;
CurrentSize = 0;
Map = new Dictionary <string, LRUNode <T> >();
}
public void DeleteElement(string Key)
{
if (Map.ContainsKey(Key) == false)
{
return; // no key exists to delete.
}
var node = Map[Key];
if (CurrentSize == 1) // only element left.
{
Head = Tail = null;
node = null;
}
else if (node == Head) // head node.
{
Head = node.Next;
node.Next = null;
node.Previous = null; // ideally not required as it should already be null.
Head.Previous = null;
}
else if (node == Tail) // last node.
{
Tail = node.Previous;
node.Previous = null;
node.Next = null;
Tail.Next = null;
}
else // intermediate node.
{
node.Previous.Next = node.Next;
node.Next.Previous = node.Previous;
node.Previous = null;
node.Next = null;
}
CurrentSize--;
Map.Remove(Key);
node = null;
}
public T GetElement(string Key)
{
if (Map.ContainsKey(Key) == false)
{
return(default(T)); // Key is not present.
}
var node = Map[Key];
if (Head == node) // the node is the recent node, so no changes.
{
// no pointer re-arrangements required.
}
else if (Tail == node) // last node in Doubly LL.
{
Tail = node.Previous;
Tail.Next = null;
node.Previous = null;
node.Next = Head;
Head = node;
}
else
{
// Intermediate node.
node.Previous.Next = node.Next;
node.Next.Previous = node.Previous;
node.Next = Head;
node.Previous = null;
Head.Previous = node;
Head = node;
}
return(node.Value);
}
public void AddElement(string Key, T value)
{
// New element
if (Map.ContainsKey(Key) == false)
{
var node = new LRUNode <T>(Key, value);
Map.Add(Key, node); // add the element.
if (CurrentSize == 0) // first element
{
Head = node;
Tail = node;
CurrentSize++;
}
else if (CurrentSize < MaxSize)
{
node.Next = Head;
node.Previous = null;
Head.Previous = node;
Head = node;
CurrentSize++;
}
else // new element and the cache is full. So we will have to evict the cache.
{
Map.Remove(Tail.Key); // Remove the element from the cache.
Tail = Tail.Previous;
Tail.Next.Previous = null;
Tail.Next = null;
Tail.Next = null;
node.Next = Head;
node.Previous = null;
Head.Previous = node;
Head = node;
}
}
else // Key already exists in the cache, so we need to update.
{
var node = Map[Key];
node.Value = value; // update the value.
if (Head == node) // the node is the recent node, so no changes.
{
// no pointer re-arrangements required.
}
else if (Tail == node) // last node in Doubly LL.
{
Tail = node.Previous;
Tail.Next = null;
node.Previous = null;
node.Next = Head;
Head = node;
}
else
{
// Intermediate node.
node.Previous.Next = node.Next;
node.Next.Previous = node.Previous;
node.Next = Head;
node.Previous = null;
Head.Previous = node;
Head = node;
}
}
}