internal BSTNode(BSTNode <T> parent, T value)
{
Parent = parent;
Value = value;
}
//worst O(n) for unbalanced tree
private BSTNode <T> delete(BSTNode <T> node, T value)
{
while (true)
{
if (node != null)
{
var compareResult = node.Value.CompareTo(value);
//node is less than the search value so move right to find the deletion node
if (compareResult < 0)
{
node = node.Right ?? throw new Exception("Item do not exist");
continue;
}
//node is less than the search value so move left to find the deletion node
if (compareResult > 0)
{
node = node.Left ?? throw new Exception("Item do not exist");
continue;
}
}
if (node == null)
{
return(null);
}
//node is a leaf node
if (node.IsLeaf)
{
deleteLeaf(node);
return(node);
}
//case one - right tree is null (move sub tree up)
if (node.Left != null && node.Right == null)
{
deleteLeftNode(node);
return(node);
}
//case two - left tree is null (move sub tree up)
if (node.Right != null && node.Left == null)
{
deleteRightNode(node);
return(node);
}
//case three - two child trees
//replace the node value with maximum element of left subtree (left max node)
//and then delete the left max node
var maxLeftNode = FindMax(node.Left);
node.Value = maxLeftNode.Value;
//delete left max node
node = node.Left;
value = maxLeftNode.Value;
}
}
