Add Maximum Array Rotation in Elixir

archive/e/elixir/maximum-array-rotation.ex

@@ -0,0 +1,29 @@
+defmodule MaximumArrayRotation do
+  @doc """
+  Returns the maximum weighted sum across all rotations of a list, where weighted sum
+  is the sum of all the elements multiplied by their indices 
+  """
+  @spec maximum_array_rotation(arr :: list(integer())) :: integer()
+  def maximum_array_rotation(arr) do
+    sum = Enum.sum(arr)
+    len = length(arr)
+
+    initial =
+      Enum.with_index(arr)
+      |> Enum.map(fn {n, i} -> n * i end)
+      |> Enum.sum()
+
+    Enum.scan(arr, initial, &(&2 + &1 * len - sum)) |> Enum.max()
+  end
+
+  @spec parse_list(str :: String.t()) :: list(integer())
+  def parse_list(""), do: []
+  def parse_list(str), do: String.split(str, ", ") |> Enum.map(&String.to_integer/1)
+end
+
+with [arg] <- System.argv(),
+     [_ | _] = arr <- MaximumArrayRotation.parse_list(arg) do
+  MaximumArrayRotation.maximum_array_rotation(arr) |> IO.puts()
+else
+  _ -> IO.puts("Usage: please provide a list of integers (e.g. \"8, 3, 1, 2\")")
+end