public static T Build <T>(IEnumerable <T> items, IAccessors <T> ops) where T : notnull
{
var iter = items.GetEnumerator();
if (!iter.MoveNext())
{
throw new Exception("Cannot build a Red/Black tree from an empty collection");
}
// Use the first item as the root
var root = iter.Current;
ops.Colour(root, EColour.Black);
// Insert all items into the tree
for (; iter.MoveNext();)
{
root = Insert(root, iter.Current, ops);
Check(root, ops);
}
return(root);
}
public static T Insert <T>([DisallowNull] T root, [DisallowNull] T item, IAccessors <T> ops) where T : notnull
{
using var stack_inst = StackPool <T> .Instance.Alloc();
var stack = stack_inst.Value;
// Insert 'item'. Record the path down the tree in 'stack'
stack.Push(root);
for (; ;)
{
var side = ops.Compare(item, stack.Top !) < 0 ? Left : Right;
if (ops.Child(side, stack.Top) is T child)
{
stack.Push(child);
}
else
{
ops.Child(side, stack.Top, item);
stack.Push(item);
break;
}
}
// Climb back to the root node, fixing colours as we go
for (; stack.Count > 2;)
{
// Get the leaf and its parent
var node = stack.Pop();
var parent = stack.Pop();
// If either 'node' or 'parent' is black, no more changes are needed
if (ops.Colour(node) == EColour.Black || ops.Colour(parent) == EColour.Black)
{
break;
}
var gparent = stack.Pop();
var parent_side = Side(parent, gparent, ops);
// Red Uncle
if (ops.Child(-parent_side, gparent) is T uncle && ops.Colour(uncle) == EColour.Red)
{
// Recolour
ops.Colour(gparent, EColour.Red);
ops.Colour(parent, EColour.Black);
ops.Colour(uncle, EColour.Black);
stack.Push(gparent);
continue;
}
// Black Uncle
// If 'node_side' is not equal to 'parent_side', swap 'node' and 'parent' to transform case 2 -> case 3
var node_side = Side(node, parent, ops);
if (node_side != parent_side)
{
Rotate(-node_side, parent, gparent, ops);
}
// Case 3 -> swap 'parent' and 'gparent' and recolour
ops.Colour(gparent, EColour.Red);
gparent = Rotate <T>(-parent_side, gparent, stack.Top, ops);
ops.Colour(gparent, EColour.Black);
// If we rotate the root element, update 'root'
if (stack.Count == 0)
{
root = gparent;
}
}
// Return the root, ensuring it's black
ops.Child(0, default, root);