Untitled notebook

Section

defmodule Solution1 do
  @map %{
    ?2 => ["a", "b", "c"],
    ?3 => ["d", "e", "f"],
    ?4 => ["g", "h", "i"],
    ?5 => ["j", "k", "l"],
    ?6 => ["m", "n", "o"],
    ?7 => ["p", "q", "r", "s"],
    ?8 => ["t", "u", "v"],
    ?9 => ["w", "x", "y", "z"]
  }
  @spec letter_combinations(digits :: String.t()) :: [String.t()]
  def letter_combinations(""), do: []

  def letter_combinations(digits) do
    digits
    |> String.to_charlist()
    |> Stream.map(&@map[&1])
    # |>
    # [["w", "x", "y", "z"],["w", "x", "y", "z"]]
    |> Enum.reduce(&evaluate(&2, &1))
  end

  defp evaluate(a, b), do: for(x <- a, y <- b, do: x <> y)
end

Solution1.letter_combinations("2")

defmodule Solution do
  @spec letter_combinations(digits :: String.t()) :: [String.t()]
  @map %{
    "2" => ["a", "b", "c"],
    "3" => ["d", "e", "f"],
    "4" => ["g", "h", "i"],
    "5" => ["j", "k", "l"],
    "6" => ["m", "n", "o"],
    "7" => ["p", "q", "r", "s"],
    "8" => ["t", "u", "v"],
    "9" => ["w", "x", "y", "z"]
  }

  def letter_combinations(digits) do
    digits
    |> String.split("", trim: true)
    |> Enum.map(fn x ->
      @map[x]
    end)
    |> evaluate
  end

  defp evaluate([]), do: []
  defp evaluate([a]), do: a
  defp evaluate([a, b]), do: for(x <- a, y <- b, do: x <> y)
  defp evaluate([a, b, c]), do: for(x <- a, y <- b, z <- c, do: x <> y <> z)
  defp evaluate([a, b, c, d]), do: for(x <- a, y <- b, z <- c, q <- d, do: x <> y <> z <> q)
end