public void Add(string hashID, string redirectUrl)
{
if (string.IsNullOrEmpty(hashID) || string.IsNullOrWhiteSpace(hashID))
{
throw new ArgumentException("HashID cannot be null, empty or white spaces");
}
if (string.IsNullOrEmpty(redirectUrl) || string.IsNullOrWhiteSpace(redirectUrl))
{
throw new ArgumentException("Redirect URL cannot be null, empty or white spaces");
}
if (nodeMap.ContainsKey(hashID))
{
// Update existing node's value.
LRUNode existingNode = nodeMap[hashID];
doubledLinkedList.RemoveNode(existingNode);
existingNode.RedirectUrl = redirectUrl;
doubledLinkedList.AddToFront(existingNode);
}
else
{
// LRU cache is full, removing least recently used node
// from map and list.
if (count == capacity)
{
LRUNode removedNode = doubledLinkedList.RemoveLRUNode();
nodeMap.Remove(removedNode.HashID);
count--;
}
LRUNode newNode = new LRUNode(hashID, redirectUrl);
doubledLinkedList.AddToFront(newNode);
nodeMap[hashID] = newNode;
count++;
}
}
public LRUDoubleLinkedList()
{
Head = new LRUNode();
Tail = new LRUNode();
Head.Next = Tail;
Tail.Previous = Head;
}
public LRUNode RemoveLRUNode()
{
LRUNode target = Tail.Previous;
if (target == null)
{
throw new InvalidOperationException("Cannot remove node when list is empty.");
}
RemoveNode(target);
return(target);
}
public void RemoveNode(LRUNode node)
{
if (node == null)
{
throw new ArgumentException("Cannot remove null node.");
}
node.Previous.Next = node.Next;
node.Next.Previous = node.Previous;
node.Next = null;
node.Previous = null;
}
public void AddToFront(LRUNode node)
{
if (node == null)
{
throw new ArgumentException("New node cannot be null.");
}
node.Next = Head.Next;
Head.Next.Previous = node;
node.Previous = Head;
Head.Next = node;
}
public string Get(string hashID)
{
if (!nodeMap.ContainsKey(hashID))
{
return(null);
}
if (string.IsNullOrEmpty(hashID) || string.IsNullOrWhiteSpace(hashID))
{
throw new ArgumentException("HashID cannot be null, empty or white spaces");
}
LRUNode existingNode = nodeMap[hashID];
// Move node to front of list when read.
doubledLinkedList.RemoveNode(existingNode);
doubledLinkedList.AddToFront(existingNode);
return(existingNode.RedirectUrl);
}
