private void MoveUpByFrequency(LFUCacheItem item)
{
if (item == _head)
{
return;
}
if (item.previous == null)
{
return;
}
LFUCacheItem oldprev = item.previous;
LFUCacheItem oldnex = item.next;
LFUCacheItem temp = oldprev;
while ((temp != null) && (temp.freq <= item.freq))
{
temp = temp.previous;
}
if (temp == oldprev)
{
return;
}
oldprev.next = oldnex;
if (oldnex != null)
{
oldnex.previous = oldprev;
}
else
{
_tail = oldprev;
}
if (temp == null)
{
//item would be inserted at the very front
//////////////////////////////////////////
item.next = _head;
_head.previous = item;
_head = item;
item.previous = null;
}
else
{
//item will be inserted after temp
//////////////////////////////////////////
LFUCacheItem tempoldnext = temp.next;
item.next = tempoldnext;
tempoldnext.previous = item;
temp.next = item;
item.previous = temp;
}
}
private void Touch(int key)
{
LFUCacheItem item = _dict[key];
item.freq += 1;
if (item == _head)
{
//do nothing
}
else
{
MoveUpByFrequency(item);
}
}
public void Put(int key, int value)
{
if (_capacity <= 0)
{
return;
}
if (_dict.ContainsKey(key))
{
//Set instead of insert
_dict[key].value = value;
//update freq etc
Touch(key);
return;
}
if (_currentCount < _capacity)
{
//add to the Doubly linked list
LFUCacheItem newitem = new LFUCacheItem();
newitem.key = key;
newitem.value = value;
newitem.freq = 1;
newitem.next = null; //by default
newitem.previous = null; //by default
_dict.Add(key, newitem);
if (_head == null)
{
//very very first item
_head = newitem;
_tail = newitem;
}
else
{
//add to the back
_tail.next = newitem;
newitem.next = null;
newitem.previous = _tail;
_tail = newitem;
}
_currentCount++;
MoveUpByFrequency(newitem);
}
else
{
//Reached Capacity
//find the least recent used item
int tailkey = _tail.key;
//remove it from Doubly Linked List
LFUCacheItem prev = _tail.previous;
if (_capacity > 1)
{
prev.next = null;
_tail = prev;
}
else
{
//to handle 1 capacity
_tail = null;
_head = null;
}
//remove it from dict
_dict.Remove(tailkey);
_currentCount--;
//try again
Put(key, value);
}
}
