// pop the current tail.
private DLinkedListNode popTail()
{
DLinkedListNode res = tail.previous;
this.removeNode(res);
return(res);
}
public void put(int key, int value)
{
DLinkedListNode node = cache[key];
if (node == null)
{
DLinkedListNode newNode = new DLinkedListNode();
newNode.key = key;
newNode.value = value;
this.cache.Add(key, newNode);
this.addNode(newNode);
++count;
if (count > capacity)
{
// pop the tail
DLinkedListNode tail = this.popTail();
this.cache.Remove(tail.key);
--count;
}
}
else
{
// update the value.
node.value = value;
this.moveToHead(node);
}
}
/**
* Always add the new node right after head;
*/
private void addNode(DLinkedListNode node)
{
node.previous = head;
node.next = head.next;
head.next.previous = node;
head.next = node;
}
/**
* Remove an existing node from the linked list.
*/
private void removeNode(DLinkedListNode node)
{
DLinkedListNode previous = node.previous;
DLinkedListNode next = node.next;
previous.next = next;
next.previous = previous;
}
public int get(int key)
{
DLinkedListNode node = cache[key];
if (node == null)
{
return(-1); // should raise exception here.
}
// move the accessed node to the head;
this.moveToHead(node);
return(node.value);
}
public LRUCache(int capacity)
{
this.count = 0;
this.capacity = capacity;
head = new DLinkedListNode();
head.previous = null;
tail = new DLinkedListNode();
tail.next = null;
head.next = tail;
tail.previous = head;
}
/**
* Move certain node in between to the head.
*/
private void moveToHead(DLinkedListNode node)
{
this.removeNode(node);
this.addNode(node);
}