private RedBlackNode <T> DeleteRebalanceLeft(RedBlackNode <T> root, ref bool done)
{
// Rotation to reduce the red sibling case to the easier to handle black sibling case
RedBlackNode <T> parent = root;
RedBlackNode <T> sibling = root.Right;
if (IsNodeRed(sibling))
{
root = root.RotateLeft();
sibling = parent.Right;
}
if (sibling != null)
{
if (!IsNodeRed(sibling.Left) && !IsNodeRed(sibling.Right))
{
if (IsNodeRed(parent))
{
done = true;
}
parent.SetColour(Colour.Black);
sibling.SetColour(Colour.Red);
}
else
{
bool parentIsRed = parent.IsRed;
bool sameRoot = root == parent;
if (IsNodeRed(sibling.Right))
{
parent = parent.RotateLeft();
}
else
{
parent.Right = parent.Right.RotateRight();
parent = parent.RotateLeft();
}
parent.SetIsRed(parentIsRed);
parent.Left.SetColour(Colour.Black);
parent.Right.SetColour(Colour.Black);
if (sameRoot)
{
root = parent;
}
else
{
root.Left = parent;
}
done = true;
}
}
return(root);
}
/// <summary>
/// Rotates the tree rooted at this node in a clockwise manner and recolours the root and pivot nodes accordingly.
/// </summary>
/// <returns>The new root of the tree</returns>
internal RedBlackNode <T> RotateRight()
{
RedBlackNode <T> pivot = this.Left;
this.Left = pivot.Right;
pivot.Right = this;
//fix heights
pivot.ResetHeight();
this.ResetHeight();
pivot.Right.SetColour(Colour.Red);
pivot.SetColour(Colour.Black);
return(pivot);
}
/// <summary>
/// Moves a black root node down to it's two children and colours the root red
/// </summary>
/// <param name="root"></param>
private static void MoveBlackDown(RedBlackNode <T> root)
{
root.SetColour(Colour.Red);
root.Left.SetColour(Colour.Black);
root.Right.SetColour(Colour.Black);
}