WhichIsFaster?

solution.exs

defmodule Solution do
  def recur(x, acc \\ 0)
  def recur(0, acc), do: acc
  def recur(target, acc) do
    if (rem(target, 3) == 0 or rem(target, 5) == 0) do
      recur(target - 1, acc + target)
    else
      recur(target - 1, acc)
    end
  end

  def unfold(target) do
    Stream.unfold(target, fn(0) -> nil; x -> {x, x - 1} end)
    |> Stream.filter(fn(x) -> rem(x, 3) == 0 or rem(x, 5) == 0 end)
    |> Enum.reduce(&Kernel.+/2)
  end

  def enum(target) do
    1..target
    |> Enum.to_list
    |> Enum.filter(&(rem(&1, 3) == 0 or rem(&1, 5) == 0))
    |> Enum.sum
  end
end

:timer.tc(fn -> Solution.recur(999) end)
:timer.tc(fn -> Solution.unfold(999) end)
:timer.tc(fn -> Solution.enum(999) end)

# {167, 233168}
# {876, 233168}
# {828, 233168}