/// <summary>
/// move the item to the front
/// </summary>
/// <param name="key"></param>
private void Touch(int key)
{
LRUCacheItem item = _dict[key];
if (item == _head)
{
//do nothing
}
else
{
LRUCacheItem prev = item.previous;
LRUCacheItem nex = item.next;
prev.next = nex;
//adjust tail if necessary
if (nex == null)
{
_tail = prev;
}
else
{
nex.previous = prev;
}
//adjust head of linked list
item.next = _head;
item.previous = null;
_head.previous = item;
_head = item;
}
}
public void Put(int key, int value)
{
if (_dict.ContainsKey(key))
{
//Set instead of insert
_dict[key].value = value;
Touch(key);
return;
}
//make adjustment if reached capacity
if (_currentCount >= _capacity)
{
//Reached Capacity
//find the least recent used(LRU) item
int tailkey = _tail.key;
//remove it from Doubly Linked List
LRUCacheItem prev = _tail.previous;
if (prev != null)
{
prev.next = null;
_tail = prev;
}
else
{
//to handle 1 capacity
_tail = null;
}
//remove it from dictionary as well
_dict.Remove(tailkey);
_currentCount--;
}
//add to the Doubly linked list
LRUCacheItem item = new LRUCacheItem();
item.key = key;
item.value = value;
item.next = null; //by default
item.previous = null; //by default
_dict.Add(key, item);
if (_head == null)
{
//very very first item
_head = item;
_tail = item;
}
else
{
//add to the front
item.next = _head;
_head.previous = item;
_head = item;
}
_currentCount++;
}