/// <summary>
/// Attempts to remove the specified data element from the BST.
/// </summary>
/// <param name="data">The data to remove from the BST.</param>
/// <returns>True if the element is found in the tree, and removed; false if the element is not
/// found in the tree.</returns>
public bool Remove(T data)
{
// first make sure there exist some items in this tree
if (root == null)
{
return(false); // no items to remove
}
// Now, try to find data in the tree
BinaryTreeNode <T> current = root, parent = null;
int result = comparer.Compare(current.Value, data);
while (result != 0)
{
if (result > 0)
{
// current.Value > data, if data exists it's in the left subtree
parent = current;
current = current.Left;
}
else if (result < 0)
{
// current.Value < data, if data exists it's in the right subtree
parent = current;
current = current.Right;
}
// If current == null, then we didn't find the item to remove
if (current == null)
{
return(false);
}
else
{
result = comparer.Compare(current.Value, data);
}
}
// At this point, we've found the node to remove
count--;
// We now need to "rethread" the tree
// CASE 1: If current has no right child, then current's left child becomes
// the node pointed to by the parent
if (current.Right == null)
{
if (parent == null)
{
root = current.Left;
}
else
{
result = comparer.Compare(parent.Value, current.Value);
if (result > 0)
{
// parent.Value > current.Value, so make current's left child a left child of parent
parent.Left = current.Left;
}
else if (result < 0)
{
// parent.Value < current.Value, so make current's left child a right child of parent
parent.Right = current.Left;
}
}
}
// CASE 2: If current's right child has no left child, then current's right child
// replaces current in the tree
else if (current.Right.Left == null)
{
current.Right.Left = current.Left;
if (parent == null)
{
root = current.Right;
}
else
{
result = comparer.Compare(parent.Value, current.Value);
if (result > 0)
{
// parent.Value > current.Value, so make current's right child a left child of parent
parent.Left = current.Right;
}
else if (result < 0)
{
// parent.Value < current.Value, so make current's right child a right child of parent
parent.Right = current.Right;
}
}
}
// CASE 3: If current's right child has a left child, replace current with current's
// right child's left-most descendent
else
{
// We first need to find the right node's left-most child
BinaryTreeNode <T> leftmost = current.Right.Left, lmParent = current.Right;
while (leftmost.Left != null)
{
lmParent = leftmost;
leftmost = leftmost.Left;
}
// the parent's left subtree becomes the leftmost's right subtree
lmParent.Left = leftmost.Right;
// assign leftmost's left and right to current's left and right children
leftmost.Left = current.Left;
leftmost.Right = current.Right;
if (parent == null)
{
root = leftmost;
}
else
{
result = comparer.Compare(parent.Value, current.Value);
if (result > 0)
{
// parent.Value > current.Value, so make leftmost a left child of parent
parent.Left = leftmost;
}
else if (result < 0)
{
// parent.Value < current.Value, so make leftmost a right child of parent
parent.Right = leftmost;
}
}
}
// Clear out the values from current
current.Left = current.Right = null;
current = null;
return(true);
}
/// <summary>
/// Removes the contents of the BST
/// </summary>
public void Clear()
{
root = null;
count = 0;
}
