étude 6-3 and appending to a list

[miguelcobain]

In Chapter 6 there is an interlude referring to the problem of adding to the tail of a list.
To work around it the solution presented is to add to that tail and reverse afterwards.

I think a better solution would be to use the ++ operator ti add to the tail.
Solution to étude 6-3:

defmodule Teeth do

  def alert(depths) do
    alert(depths, 1, [])
  end

  def alert([], _, result) do
    result
  end

  def alert([tooth | teeth], number, result) do
    cond do
      Stats.maximum(tooth) >= 4 -> alert(teeth, number + 1, result ++ [number])
      true -> alert(teeth, number + 1, result)
    end
  end

  def pocket_depths do
    [[0], [2,2,1,2,2,1], [3,1,2,3,2,3],
    [3,1,3,2,1,2], [3,2,3,2,2,1], [2,3,1,2,1,1],
    [3,1,3,2,3,2], [3,3,2,1,3,1], [4,3,3,2,3,3],
    [3,1,1,3,2,2], [4,3,4,3,2,3], [2,3,1,3,2,2],
    [1,2,1,1,3,2], [1,2,2,3,2,3], [1,3,2,1,3,3], [0],
    [3,2,3,1,1,2], [2,2,1,1,3,2], [2,1,1,1,1,2],
    [3,3,2,1,1,3], [3,1,3,2,3,2], [3,3,1,2,3,3],
    [1,2,2,3,3,3], [2,2,3,2,3,3], [2,2,2,4,3,4],
    [3,4,3,3,3,4], [1,1,2,3,1,2], [2,2,3,2,1,3],
    [3,4,2,4,4,3], [3,3,2,1,2,3], [2,2,2,2,3,3],
    [3,2,3,2,3,2]]
  end

end