private void InsertAfterOnCurrentLevel(SkipListNode <K, V> prevNode, SkipListNode <K, V> newNode)
{
var successorNode = prevNode.Next;
prevNode.Next = newNode;
newNode.Prev = prevNode;
newNode.Next = successorNode;
successorNode.Prev = newNode;
}
private SkipListNode <K, V> FindHighestNodeLessThanAtCurrentLevel(SkipListNode <K, V> startNode, K key)
{
var currentNode = startNode;
//currentnodekey<=key
while (_comparer.Compare(currentNode.Next.Entry.Key, key) <= 0)
{
currentNode = currentNode.Next;
}
return(currentNode);
}
private void CreateNewLevel()
{
var negInfNode = CreateNegInfNode();
var posInfNode = CreatePosInfNode();
if (_head != null && _tail != null)
{
_head.Up = negInfNode;
_tail.Up = posInfNode;
negInfNode.Down = _head;
posInfNode.Down = _tail;
}
_head = negInfNode;
_tail = posInfNode;
_head.Next = _tail;
_tail.Prev = _head;
}
public override V Put(K key, V value)
{
var node = Find(key);
if (_comparer.Compare(key, node.Entry.Key) == 0)
{
var old = node.Entry.Value;
node.Entry.Value = value;
return(old);
}
var prevNewNode = new SkipListNode <K, V>(key, value);
InsertAfterOnCurrentLevel(node, prevNewNode);
var i = 1;
while (_random.NextDouble() < 0.5)
{
if (i > _height)
{
CreateNewLevel();
_height++;
}
while (node.Up == null)
{
node = node.Prev;
}
node = node.Up;
var newNode = new SkipListNode <K, V>(key, default(V)); //value only needs to be stored on lowest level
InsertAfterOnCurrentLevel(node, newNode);
prevNewNode.Up = newNode;
newNode.Down = prevNewNode;
prevNewNode = newNode;
i++;
}
n++;
return(value);
}
