/// <summary>
/// Gets the sibling of the given node
/// </summary>
/// <returns>The sibling</returns>
/// <param name="node">Node</param>
protected RedBlackTreeNode <K, V> GetSibling(RedBlackTreeNode <K, V> node)
{
if (node.IsRightChild())
{
return((RedBlackTreeNode <K, V>)node.Parent.Left);
}
return((RedBlackTreeNode <K, V>)node.Parent.Right);
}
protected void FixAfterInsertion(RedBlackTreeNode <K, V> node)
{
if (node == null || node.Parent == null || node.Parent.Parent == null)
{
return;
}
//There are 2 probable issues to fix after insertion
//And all of them must have 2 red nodes (child, parent) AKA red red problem
//Legend:
//(N) = New Node (P) = Parent (S) = Sibling (Uncle) (G) = Grandparent
var sibling = GetSibling((RedBlackTreeNode <K, V>)node.Parent);
bool parentIsRed = ((RedBlackTreeNode <K, V>)node.Parent).Color == NodeColor.Red;
NodeColor siblingColor = sibling != null ? sibling.Color : NodeColor.Black;
//Case 1: (N) == Red && (P) == Red && (S) == Red
//In this case we recolor and go upwards
if (parentIsRed && sibling != null && sibling.Color == NodeColor.Red)
{
((RedBlackTreeNode <K, V>)node.Parent.Parent).Color = NodeColor.Red;
((RedBlackTreeNode <K, V>)node.Parent).Color = NodeColor.Black;
sibling.Color = NodeColor.Black;
FixAfterInsertion((RedBlackTreeNode <K, V>)node.Parent.Parent);
}
//Case 2: (N) == Red && (P) == Red && (S) == Black (null siblings are black too)
//It's a bit tricky to explain in comments
//For more info about the cases: https://brilliant.org/wiki/red-black-tree/
else if (parentIsRed && siblingColor == NodeColor.Black)
{
var grandparent = node.Parent.Parent;
((RedBlackTreeNode <K, V>)node.Parent.Parent).Color = NodeColor.Red;
//Case 2.1
if (node.Parent.IsLeftChild() && node.IsLeftChild())
{
((RedBlackTreeNode <K, V>)node.Parent).Color = NodeColor.Black;
RotateRight(grandparent);
}
//Case 2.2
else if (node.Parent.IsLeftChild() && node.IsRightChild())
{
node.Color = NodeColor.Black;
RotateLeft(node.Parent);
RotateRight(grandparent);
}
//Case 2.3
else if (node.Parent.IsRightChild() && node.IsRightChild())
{
((RedBlackTreeNode <K, V>)node.Parent).Color = NodeColor.Black;
RotateLeft(grandparent);
}
//Case 2.4
else if (node.Parent.IsRightChild() && node.IsLeftChild())
{
node.Color = NodeColor.Black;
RotateRight(node.Parent);
RotateLeft(grandparent);
}
}
}
