public bool Delete(T valueToDelete)
{
if (_root == null)
{
// empty tree: the value is not in there
return(false);
}
var current = _root;
BinaryNode <T> parent = null;
int comparisonResult = _comparer.Compare(current.Value, valueToDelete);
// 1.: search for the value
while (comparisonResult != 0)
{
if (comparisonResult > 0)
{
// continue the search in the left subtree
parent = current;
current = current.Left;
}
else if (comparisonResult < 0)
{
// continue the search in the right subtree
parent = current;
current = current.Right;
}
comparisonResult = _comparer.Compare(current.Value, valueToDelete);
}
if (current == null)
{
// we didn't find the item to delete
return(false);
}
// 2.: delete the item
// 2.1.: the item has no right child
// => left child can replace it
if (current.Right == null)
{
// if there is no parent, we are about to delete the root
if (parent == null)
{
_root = current.Left;
}
else
{
comparisonResult = _comparer.Compare(parent.Value, current.Value);
if (comparisonResult > 0)
{
// the left child should go in parent's left subtree
parent.Left = current.Left;
}
else if (comparisonResult < 0)
{
// the left child should go in the parent's right subtree
parent.Right = current.Left;
}
}
}
// 2.2.: the item's right child has no left child
// => right child can replace it
else if (current.Right.Left == null)
{
// if there is no parent, we are about to delete the root
if (parent == null)
{
_root = current.Right;
}
else
{
comparisonResult = _comparer.Compare(parent.Value, current.Value);
if (comparisonResult > 0)
{
// the right child should go in the parent's left subtree
parent.Left = current.Right;
}
else if (comparisonResult < 0)
{
// the right child should go in the parent's right subtree
parent.Right = current.Right;
}
}
}
// 2.3.: the item's right child has a left child
// => we search for its leftmost child to replace the item
else
{
var leftmost = current.Right.Left;
BinaryNode <T> lmParent = current.Right;
while (leftmost.Left != null)
{
lmParent = leftmost;
leftmost = leftmost.Left;
}
// right subtree of leftmost will go in its parent's left subtree
lmParent.Left = leftmost.Right;
// replace current with leftmost
leftmost.Left = current.Left;
leftmost.Right = current.Right;
if (parent == null)
{
_root = leftmost;
}
else
{
comparisonResult = _comparer.Compare(parent.Value, leftmost.Value);
if (comparisonResult > 0)
{
// leftmost will go in parent's left subtree
parent.Left = leftmost;
}
else if (comparisonResult < 0)
{
// leftmost will go in parent's right subtree
parent.Right = leftmost;
}
}
}
return(true);
}
public BinarySearchTree()
{
_root = null;
_comparer = Comparer <T> .Default;
}
