invert.exs

defmodule BinaryTree do
  defstruct [:left, :right, :value]

  def invert(%__module__{left: left, right: right} = root) do
    %{root| left: invert(right), right: invert(left)}
  end
  def invert(nil), do: nil

  def test do
    three = %BinaryTree{value: 3}
    one = %BinaryTree{value: 1}
    six = %BinaryTree{value: 6}
    nine = %BinaryTree{value: 9}
    seven = %BinaryTree{value: 7, left: six, right: nine}
    two = %BinaryTree{value: 2, left: one, right: three}
    four = %BinaryTree{value: 4, left: two, right: seven}

    2 = four.left.value
    1 = four.left.left.value

    inverted = invert(four)

    7 = inverted.left.value
    9 = inverted.left.left.value

    :ok
  end
end