difference-of-squares

elixir/difference-of-squares/lib/squares.ex

@@ -0,0 +1,29 @@
+defmodule Squares do
+  @moduledoc """
+  Calculate sum of squares, square of sum, difference between two sums from 1 to a given end number.
+  """
+
+  @doc """
+  Calculate sum of squares from 1 to a given end number.
+  """
+  @spec sum_of_squares(pos_integer) :: pos_integer
+  def sum_of_squares(number) do
+    div(number * (number + 1) * (2 * number + 1), 6)
+  end
+
+  @doc """
+  Calculate square of sum from 1 to a given end number.
+  """
+  @spec square_of_sum(pos_integer) :: pos_integer
+  def square_of_sum(number) do
+    div(number * (number + 1), 2) ** 2
+  end
+
+  @doc """
+  Calculate difference between sum of squares and square of sum from 1 to a given end number.
+  """
+  @spec difference(pos_integer) :: pos_integer
+  def difference(number) do
+    abs(square_of_sum(number) - sum_of_squares(number))
+  end
+end