2016 Update

Task/Tree-traversal/Elixir/tree-traversal.elixir

@@ -0,0 +1,56 @@
+defmodule Tree_Traversal do
+  defp tnode, do: {}
+  defp tnode(v), do: {:node, v, {}, {}}
+  defp tnode(v,l,r), do: {:node, v, l, r}
+
+  defp preorder(_,{}), do: :ok
+  defp preorder(f,{:node,v,l,r}) do
+    f.(v)
+    preorder(f,l)
+    preorder(f,r)
+  end
+
+  defp inorder(_,{}), do: :ok
+  defp inorder(f,{:node,v,l,r}) do
+    inorder(f,l)
+    f.(v)
+    inorder(f,r)
+  end
+
+  defp postorder(_,{}), do: :ok
+  defp postorder(f,{:node,v,l,r}) do
+    postorder(f,l)
+    postorder(f,r)
+    f.(v)
+  end
+
+  defp levelorder(_, []), do: []
+  defp levelorder(f, [{}|t]), do: levelorder(f, t)
+  defp levelorder(f, [{:node,v,l,r}|t]) do
+    f.(v)
+    levelorder(f, t++[l,r])
+  end
+  defp levelorder(f, x), do: levelorder(f, [x])
+
+  def main do
+    tree = tnode(1,
+                 tnode(2,
+                       tnode(4, tnode(7), tnode()),
+                       tnode(5, tnode(), tnode())),
+                 tnode(3,
+                       tnode(6, tnode(8), tnode(9)),
+                       tnode()))
+    f = fn x -> IO.write "#{x} " end
+    IO.write "preorder:   "
+    preorder(f, tree)
+    IO.write "\ninorder:    "
+    inorder(f, tree)
+    IO.write "\npostorder:  "
+    postorder(f, tree)
+    IO.write "\nlevelorder: "
+    levelorder(f, tree)
+    IO.puts ""
+  end
+end
+
+Tree_Traversal.main