[Sync Iteration] elixir/sublist/1

solutions/elixir/sublist/1/lib/sublist.ex

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+defmodule Sublist do
+  @doc """
+  Returns whether the first list is a sublist or a superlist of the second list
+  and if not whether it is equal or unequal to the second list.
+  """
+  def compare(a, a), do: :equal
+  def compare(a, b) do
+    cond do
+      sublist?(a, b) -> :sublist
+      sublist?(b, a) -> :superlist
+      true -> :unequal
+    end
+  end
+
+  defp sublist?(a, a), do: true
+  defp sublist?(a, b) when length(a) > length(b), do: false
+  defp sublist?(a, [_ | b_tail] = b) do
+    if List.starts_with?(b, a), do: true, else: sublist?(a, b_tail)
+  end
+end