delete BST

delete.ex

	@doc """
	Removes a node with 'node_value' from the given 'tree'. Returns :leaf if the
	node does not exist.
	"""
	@spec delete_node(%{}, any) :: %{} | nil

	def delete_node(tree, node_value) do 
		if exists?(tree, node_value) do 
			delete tree, node_value
		else
			nil
		end
	end

	defp delete(tree, node_value) do
		cond do 
			tree.value == node_value -> del(tree)
			tree.value <  node_value -> 
				%{left: tree.left, 
										value: tree.value, 
										right: delete(tree.right, node_value)}
			tree.value > node_value ->
				%{left: delete(tree.left,node_value),
										value: tree.value, 
										right: tree.right}
		end
	end

	defp del(%{left: :leaf,  value: _, right: right}), do: right
	defp del(%{left: left, value: _, right: :leaf}),   do: left
	defp del(%{left: left, value: _, right: right}) do 
		%{left: left, value: min(right), right: delete(right, min(right))}
	end

	defp min(%{left: :leaf,  value: val, right: _}), do: val
	defp min(%{left: left, value: _,   right: _}), do: min left