protected override IEnumerable <T> PreOrderTraversal()
{
if (Head != null)
{
var stack = new Stack <BinarySearchTreeNode <T> >();
BinarySearchTreeNode <T> current = Head;
bool goLeftNext = true;
stack.Push(current);
yield return(current.Value);
while (stack.Count > 0)
{
if (goLeftNext)
{
while (current.Left != null)
{
stack.Push(current);
current = current.Left;
yield return(current.Value);
}
}
if (current.Right != null)
{
current = current.Right;
goLeftNext = true;
yield return(current.Value);
}
else
{
current = stack.Pop();
goLeftNext = false;
}
}
}
}
public override sealed void Add(T value)
{
if (Head == null)
{
Head = new BinarySearchTreeNode <T>(value);
}
else
{
BinarySearchTreeNode <T> current = Head;
while (true)
{
if (value.CompareTo(current.Value) < 0)
{
if (current.Left == null)
{
current.Left = new BinarySearchTreeNode <T>(value);
break;
}
current = current.Left;
}
else
{
if (current.Right == null)
{
current.Right = new BinarySearchTreeNode <T>(value);
break;
}
current = current.Right;
}
}
}
Count++;
}
public override sealed bool Remove(T value)
{
BinarySearchTreeNode <T> parent;
BinarySearchTreeNode <T> current = FindWithParent(value, out parent);
if (current == null)
{
return(false);
}
Count--;
if (current.Right == null)
{
if (parent == null)
{
Head = current.Left;
}
else
{
int compareResult = parent.CompareTo(current.Value);
if (compareResult > 0)
{
parent.Left = current.Left;
}
else if (compareResult < 0)
{
parent.Right = current.Left;
}
}
}
else if (current.Right.Left == null)
{
current.Right.Left = current.Left;
if (parent == null)
{
Head = current.Right;
}
else
{
int compareResult = parent.CompareTo(current.Value);
if (compareResult > 0)
{
parent.Left = current.Right;
}
else if (compareResult < 0)
{
parent.Right = current.Right;
}
}
}
else
{
BinarySearchTreeNode <T> leftmost = current.Right.Left;
BinarySearchTreeNode <T> leftmostParent = current.Right;
while (leftmost.Left != null)
{
leftmostParent = leftmost;
leftmost = leftmost.Left;
}
leftmostParent.Left = leftmost.Right;
leftmost.Left = current.Left;
leftmost.Right = current.Right;
if (parent == null)
{
Head = leftmost;
}
else
{
int compareResult = parent.CompareTo(current.Value);
if (compareResult > 0)
{
parent.Left = leftmost;
}
else if (compareResult < 0)
{
parent.Right = leftmost;
}
}
}
return(true);
}
public override sealed void Clear()
{
Head = null;
Count = 0;
}