pascals_triangle

elixir/pascals-triangle/lib/pascals_triangle.ex

@@ -0,0 +1,19 @@
+defmodule PascalsTriangle do
+  @doc """
+  Calculates the rows of a pascal triangle
+  with the given height
+  """
+  @spec rows(integer) :: [[integer]]
+  def rows(num) do
+    1..num
+    |> Enum.reduce([[]], fn _, triangle -> [next(hd(triangle)) | triangle] end)
+    |> Enum.take(num)
+    |> Enum.reverse
+  end
+
+  defp next(from, acc \\ [])
+  defp next([], _acc), do: [1]
+  defp next([1], _acc), do: [1, 1]
+  defp next([one, two | []], acc), do: [1 | Enum.reverse([1, one + two | acc])]
+  defp next([one, two | rest], acc), do: next([two | rest], [one + two | acc])
+end