private RBNode <T> RR(RBNode <T> root)
{
RBNode <T> right = root.Right;
root.Right = right.Left;
right.Left = root;
return(right);
}
private void Print(RBNode <T> root)
{
if (root.IsNotNull())
{
Print(root.Left);
Console.Write(root.Item + " ");
Print(root.Right);
}
}
private RBNode <T> LL(RBNode <T> root)
{
RBNode <T> left = root.Left;
root.Left = left.Right;
left.Right = root;
return(left);
}
private RBNode <T> LR(RBNode <T> root)
{
RBNode <T> left = root.Left;
RBNode <T> right = left.Right;
root.Left = right.Right;
right.Right = root;
left.Right = right.Left;
right.Left = left;
return(right);
}
private void ReplaceChildOfNodeOrRoot(RBNode <T> parent, RBNode <T> child, RBNode <T> newChild)
{
if (parent.IsNotNull())
{
if (parent.Left == child)
{
parent.Left = newChild;
}
else
{
parent.Right = newChild;
}
}
else
{
_head = newChild;
}
}
public bool Add(T value)
{
// for an empty tree, just create a new root node.
if (IsEmpty)
{
_head = new RBNode <T>(value);
_head.IsRed = false;
return(true);
}
p = 0;
RBNode <T> parent = null, current = _head;
while (current.IsNotNull())
{
path[p++] = current;
if (current.Item.CompareTo(value) == 0)
{
// item exists.
return(false);
}
parent = current;
current = (value.CompareTo(parent.Item) < 0) ? parent.Left : parent.Right;
}
// all the new nodes should be RED.
current = new RBNode <T>(value);
current.IsRed = true;
if (value.CompareTo(parent.Item) < 0)
{
parent.Left = current;
}
else
{
parent.Right = current;
}
if (!parent.IsRed)
{
return(true);
}
path[p] = current; // get the complete path.
while ((p -= 2) >= 0) // check grand parent node.
{
RBNode <T> grandParent = path[p];
parent = path[p + 1];
if (!parent.IsRed)
{
break;
}
RBNode <T> uncle = (grandParent.Left == parent) ? grandParent.Right : grandParent.Left;
current = path[p + 2];
if (IsRed(uncle))
{
parent.IsRed = false;
uncle.IsRed = false;
if (p > 0)
{
grandParent.IsRed = true;
}
}
else
{
// if uncle is null or black.
RBNode <T> newRoot;
if (grandParent.Left == parent)
{
newRoot = (parent.Left == current) ? LL(grandParent) : LR(grandParent);
}
else
{
newRoot = (parent.Right == current) ? RR(grandParent) : RL(grandParent);
}
grandParent.IsRed = true;
newRoot.IsRed = false;
ReplaceChildOfNodeOrRoot((p > 0) ? path[p - 1] : null, grandParent, newRoot);
return(true);
}
}
return(true);
}
public RBNode(T item, RBNode <T> leftChild, RBNode <T> rightChild)
{
Item = item;
Left = leftChild;
Right = rightChild;
}
private bool IsNullOrBlack(RBNode <T> node)
{
return(node.IsNull() || !node.IsRed);
}
private bool IsBlack(RBNode <T> node)
{
return(node.IsNotNull() && !node.IsRed);
}
private bool IsRed(RBNode <T> uncle)
{
return(uncle.IsNotNull() && uncle.IsRed);
}
private void RemoveNode(RBNode <T> node)
{
RBNode <T> tmp = null; // after the below step, tmp points to the actual node to be deleted;
if (node.Degree == 2)
{
tmp = node.Left;
path[++p] = tmp;
while (tmp.Right != null)
{
tmp = tmp.Right;
path[++p] = tmp;
}
node.Item = tmp.Item;
}
else
{
tmp = node;
}
RBNode <T> newTmp = tmp.Left;
if (newTmp.IsNull())
{
newTmp = tmp.Right;
}
if (p > 0)
{
RBNode <T> parent = path[p - 1];
if (parent.Left == tmp)
{
parent.Left = newTmp;
}
else
{
parent.Right = newTmp;
}
// if the deleted is black and its single child is red.
if (!tmp.IsRed && IsRed(newTmp))
{
newTmp.IsRed = false;
return;
}
}
else
{
// if delete the root node.
_head = newTmp;
if (_head.IsNotNull())
{
_head.IsRed = false;
}
return;
}
path[p] = newTmp;
if (IsRed(tmp))
{
// if the deleted is red, directly return.
return;
}
// the deleted and its child are both BLACK.
while (p > 0)
{
RBNode <T> current = path[p];
RBNode <T> parent = path[p - 1];
bool currentIsLeft = (parent.Left == current);
RBNode <T> sibling = currentIsLeft ? parent.Right : parent.Left;
if (IsRed(sibling))
{
RBNode <T> newRoot;
if (currentIsLeft)
{
newRoot = RR(parent);
}
else
{
newRoot = LL(parent);
}
ReplaceChildOfNodeOrRoot(p > 1 ? path[p - 2] : null, parent, newRoot);
sibling.IsRed = false;
parent.IsRed = true;
path[p - 1] = newRoot;
path[p] = parent;
path[++p] = current;
}
else
{
// black sibling && black sibling-left && black sibling-right
if (IsNullOrBlack(sibling.Left) && IsNullOrBlack(sibling.Right))
{
if (parent.IsRed)
{
parent.IsRed = false;
sibling.IsRed = true;
if (current.IsNotNull())
{
// TODO: not needed?
current.IsRed = false;
}
break;
}
else
{
// current must be black?
parent.IsRed = IsRed(current);
if (current.IsNotNull())
{
current.IsRed = false;
}
sibling.IsRed = true;
p--; // continue to backtrack.
}
}
else
{
RBNode <T> newRoot;
if (currentIsLeft)
{
if (IsRed(sibling.Right))
{
newRoot = RR(parent);
sibling.Right.IsRed = false;
}
else
{
newRoot = RL(parent);
}
}
else
{
if (IsRed(sibling.Left))
{
newRoot = LL(parent);
sibling.Left.IsRed = false;
}
else
{
newRoot = LR(parent);
}
}
if (current.IsNotNull())
{
current.IsRed = false;
}
newRoot.IsRed = parent.IsRed;
parent.IsRed = false;
ReplaceChildOfNodeOrRoot(p > 1 ? path[p - 2] : null, parent, newRoot);
break;
}
}
}
}