converting list into a BST

ListIntoBST/listIntoBST.exs

@@ -0,0 +1,45 @@
+# Solution for: https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/
+# Definition for singly-linked list.
+#
+# defmodule ListNode do
+#   @type t :: %__MODULE__{
+#           val: integer,
+#           next: ListNode.t() | nil
+#         }
+#   defstruct val: 0, next: nil
+# end
+
+# Definition for a binary tree node.
+#
+# defmodule TreeNode do
+#   @type t :: %__MODULE__{
+#           val: integer,
+#           left: TreeNode.t() | nil,
+#           right: TreeNode.t() | nil
+#         }
+#   defstruct val: 0, left: nil, right: nil
+# end
+
+defmodule Solution do
+
+  defp parse_list(nil), do: []
+
+  defp parse_list(head) do
+    [head.val] ++ parse_list(head.next)
+  end
+
+  defp get_BST(list, left, right) do
+    if left <= right do
+      mid = div(left + right, 2)
+      %TreeNode{val: Enum.at(list, mid), left: get_BST(list, left, mid - 1), right: get_BST(list, mid + 1, right)}
+    else
+      nil
+    end
+  end
+
+  @spec sorted_list_to_bst(head :: ListNode.t | nil) :: TreeNode.t | nil
+  def sorted_list_to_bst(head) do
+    list = parse_list(head)
+    get_BST(list, 0, Enum.count(list) - 1)
+  end
+end