ABC134D - Preparing Boxes

問題

回答

defmodule Main do
  def main do
    :stdio
    |> IO.read(:all)
    |> solve()
    |> IO.puts()
  end

  defp split_lines(lines) do
    lines
    |> String.trim()
    |> String.split("\n")
  end

  defp split_words(words) do
    String.split(words, " ")
  end

  defp renew_table(objects, table_name) do
    if :ets.info(table_name) != :undefined do
      :ets.delete(table_name)
    end

    :ets.new(table_name, [:set, :protected, :named_table])
    :ets.insert(table_name, objects)
  end

  defp lookup(table_name, key) do
    case :ets.lookup(table_name, key) do
      [{_, value}] -> value
      _ -> 0
    end
  end

  def solve(input) do
    [[n], a] =
      input
      |> split_lines()
      |> Enum.map(fn line ->
        line
        |> split_words()
        |> Enum.map(&String.to_integer/1)
      end)

    a
    |> Enum.with_index()
    |> Enum.map(fn {a_i, i} -> {i + 1, a_i} end)
    |> renew_table(:a)

    renew_table([], :b)

    n..1
    |> Enum.each(fn i ->
      other =
        2..div(n, i)
        |> Enum.count(fn j -> lookup(:b, i * j) == 1 end)

      if rem(other, 2) != lookup(:a, i) do
        :ets.insert(:b, {i, 1})
      end
    end)

    ans =
      :b
      |> :ets.tab2list()
      |> Enum.filter(fn {_, b_i} -> b_i == 1 end)
      |> Enum.map(&elem(&1, 0))

    ~s"#{length(ans)}\n#{Enum.join(ans, " ")}"
  end
end

"""
3
1 0 0
"""
|> Main.solve()
|> then(&(&1 == ~s"1
1"))

"""
5
0 0 0 0 0
"""
|> Main.solve()
|> then(&(&1 == ~s"0
"))