2109 - Adding Spaces to a String

Mix.install([])

ExUnit.start(auto_run: false)

Solution

https://leetcode.com/problems/adding-spaces-to-a-string

defmodule Solution do
  @spec add_spaces(s :: String.t(), spaces :: [integer]) :: String.t()
  def add_spaces(s, spaces) do
    do_add_spaces(s, [], 0, spaces)
  end

  defp do_add_spaces(graphems, graphems_with_spaces, _current_index, _spaces = []) do
    :binary.list_to_bin(Enum.reverse(graphems_with_spaces) ++ graphems)
  end

  defp do_add_spaces(graphems, graphems_with_spaces, current_index, spaces) do
    {next_graphem, graphems_rest} = String.next_grapheme(graphems)
    [next_space | spaces_rest] = spaces

    if next_space == current_index do
      do_add_spaces(
        graphems_rest,
        [next_graphem, " " | graphems_with_spaces],
        current_index + 1,
        spaces_rest
      )
    else
      do_add_spaces(
        graphems_rest,
        [next_graphem | graphems_with_spaces],
        current_index + 1,
        spaces
      )
    end
  end
end

defmodule TestFindSchedule do
  use ExUnit.Case, async: false

  test "1" do
    assert Solution.add_spaces("LeetcodeHelpsMeLearn", [8, 13, 15]) ==
             "Leetcode Helps Me Learn"
  end
end

ExUnit.run()