// Delete element already found at path.
private void Delete(TreePath <TKey, TValue> path)
{
int leafIndex = path.TopNodeIndex;
Leaf <TKey, TValue> leaf = (Leaf <TKey, TValue>)path.TopNode;
leaf.Remove(leafIndex);
--Count;
if (leafIndex == 0)
{
if (leaf.KeyCount != 0)
{
path.SetPivot(path.TopNode.GetKey(0));
}
else
{
Debug.Assert(leaf.RightLeaf == null, "only the rightmost leaf should ever be emptied");
// Leaf is empty. Prune it unless it is the only leaf in the tree.
Leaf <TKey, TValue> leftLeaf = (Leaf <TKey, TValue>)path.GetLeftNode();
if (leftLeaf != null)
{
leftLeaf.RightLeaf = leaf.RightLeaf;
Demote(path);
}
return;
}
}
// Leaf underflow?
if (leaf.KeyCount < leaf.KeyCapacity / 2)
{
Leaf <TKey, TValue> rightLeaf = leaf.RightLeaf;
if (rightLeaf != null)
{
if (leaf.KeyCount + rightLeaf.KeyCount > leaf.KeyCapacity)
{
// Balance leaves by shifting pairs from right leaf.
int shifts = leaf.KeyCapacity - (leaf.KeyCount + rightLeaf.KeyCount - 1) / 2;
leaf.Add(rightLeaf, 0, shifts);
rightLeaf.Remove(0, shifts);
path.TraverseRight();
path.SetPivot(path.TopNode.GetKey(0));
}
else
{
// Coalesce right leaf to current leaf and prune right leaf.
leaf.Add(rightLeaf, 0, rightLeaf.KeyCount);
leaf.RightLeaf = rightLeaf.RightLeaf;
path.TraverseRight();
Demote(path);
}
}
}
}
// Insert element at preseeked path.
private void Insert(TreePath <TKey, TValue> path, TKey key, TValue value)
{
Leaf <TKey, TValue> leaf = (Leaf <TKey, TValue>)path.TopNode;
int leafIndex = path.TopNodeIndex;
if (leaf.NotFull)
{
leaf.Insert(leafIndex, key, value);
++Count;
return;
}
// Leaf overflow. Right split a new leaf.
Leaf <TKey, TValue> newLeaf = new Leaf <TKey, TValue>(leaf);
if (newLeaf.RightLeaf == null && leafIndex == leaf.KeyCount)
{
// Densify sequential loads.
newLeaf.Add(key, value);
}
else
{
int halfway = leaf.KeyCount / 2 + 1;
if (leafIndex < halfway)
{
// Left-side insert: Copy right side to the split leaf.
newLeaf.Add(leaf, halfway - 1, leaf.KeyCount);
leaf.Truncate(halfway - 1);
leaf.Insert(leafIndex, key, value);
}
else
{
// Right-side insert: Copy split leaf parts and new key.
newLeaf.Add(leaf, halfway, leafIndex);
newLeaf.Add(key, value);
newLeaf.Add(leaf, leafIndex, leaf.KeyCount);
leaf.Truncate(halfway);
}
}
// Promote anchor of split leaf.
++Count;
Promote(path, newLeaf.GetKey(0), (Node <TKey>)newLeaf);
}
