protected N DoDelete(AvlTreeTraversal <N, P> deletionPointLocator)
{
N currentNode = deletionPointLocator.CurrentNode;
Descent direction = deletionPointLocator.Descend();
if (direction == Descent.NotFound)
{
return(null);
}
else if (direction == Descent.Found)
{
if (currentNode.Left.IsNil)
{
return(currentNode.Right);
}
else if (currentNode.Right.IsNil)
{
return(currentNode.Left);
}
else // has both children
{
(P payload, N residue) = DeleteMin(currentNode.Right);
return(Rebalance(payload, currentNode.Left, residue));
}
}
else
{
N left;
N right;
if (direction == Descent.Left)
{
left = DoDelete(deletionPointLocator);
if (left == null)
{
return(null); // propagate the 'deletion point not found' result up the stack
}
right = currentNode.Right;
}
else
{
right = DoDelete(deletionPointLocator);
if (right == null)
{
return(null);
}
left = currentNode.Left;
}
return(Rebalance(currentNode.Payload, left, right));
}
}
protected N DoInsertOrUpdate(
P payloadToInsert, Func <P, P> payloadUpdate, AvlTreeTraversal <N, P> nodeLocator)
{
N currentNode = nodeLocator.CurrentNode; // memorize the current node before descending
Descent direction = nodeLocator.Descend(); // descend: insertionLeafLocator.CurrentNode changes
if (direction == Descent.NotFound)
{
return(null);
}
P value;
N left;
N right;
if (direction == Descent.Found)
{
if (currentNode.IsNil) // insertion case
{
value = payloadToInsert;
left = NilNode;
right = NilNode;
}
else // payload replacement case
{
value = payloadUpdate(currentNode.Payload);
left = currentNode.Left;
right = currentNode.Right;
}
}
else
{
value = currentNode.Payload; // preserve payload
N rebuiltSubtree = DoInsertOrUpdate(payloadToInsert, payloadUpdate, nodeLocator);
if (rebuiltSubtree == null)
{
return(null); // propagate the 'insertion/update point not found' result up the stack
}
if (direction == Descent.Left)
{
left = rebuiltSubtree;
right = currentNode.Right;
}
else // direction == Descent.Right
{
left = currentNode.Left;
right = rebuiltSubtree;
}
}
return(Rebalance(value, left, right));
}