private void Split(TwoFourTreeNode node)
{
var parent = node.Parent;
Debug.Assert(node.IsKeyFull);
var midKey = node.Items[1];
var newNode = node.Split();
if (node == _root)
{
Debug.Assert(parent == null);
var newRoot = new TwoFourTreeNode(midKey, node, newNode);
_root = newRoot;
}
else
{
Debug.Assert(parent != null);
var nodeIndex = node.GetChildIndex();
Debug.Assert(parent.Children[nodeIndex] == node);
parent.InsertItemChild(nodeIndex, midKey, newNode);
}
}
private void AdjustNodeWhenRemove(TwoFourTreeNode node)
{
var parent = node.Parent;
Debug.Assert(parent != null);
var childIndex = node.GetChildIndex();
var leftSiblingIndex = childIndex - 1;
var rightSiblingIndex = childIndex + 1;
// If a sibling on either side of this node is a 3-node or a 4-node (thus having more than 1 key)
if (rightSiblingIndex <= parent.KeyNum && !parent.Children[rightSiblingIndex].IsKeyMin)
{
var sibling = parent.Children[rightSiblingIndex];
var pair = sibling.RemoveFirstItemChild();
node.AppendItemChild(parent.Items[childIndex], pair.Node);
parent.Items[childIndex] = pair.Item;
}
else if (leftSiblingIndex >= 0 && !parent.Children[leftSiblingIndex].IsKeyMin)
{
var sibling = parent.Children[leftSiblingIndex];
var pair = sibling.RemoveLastItemChild();
node.PushFrontItemChild(parent.Items[leftSiblingIndex], pair.Node);
parent.Items[leftSiblingIndex] = pair.Item;
}
// If all adjacent siblings are 2-nodes
else if (rightSiblingIndex <= parent.KeyNum && parent.Children[rightSiblingIndex].IsKeyMin)
{
node.MergeWithRight(rightSiblingIndex, parent.Children[rightSiblingIndex]);
if (parent.KeyNum == 0)
{
if (parent == _root)
{
_root.Invalidate();
_root = node;
_root.Parent = null;
}
else
{
AdjustNodeWhenRemove(parent);
}
}
}
else if (leftSiblingIndex >= 0 && parent.Children[leftSiblingIndex].IsKeyMin)
{
var sibling = parent.Children[leftSiblingIndex];
sibling.MergeWithRight(childIndex, node);
if (parent.KeyNum == 0)
{
if (parent == _root)
{
_root.Invalidate();
_root = sibling;
_root.Parent = null;
}
else
{
AdjustNodeWhenRemove(parent);
}
}
}
else
{
throw new Exception("cannot reach here!");
}
}
