defmodule FrogRiverOne do
  def frog_river_one(x, a) do
    a
    |> Enum.with_index()
    |> Enum.reduce_while(MapSet.new(), fn {leaf, k}, seen ->
      seen =
        if leaf <= x and not MapSet.member?(seen, leaf) do
          MapSet.put(seen, leaf)
        else
          seen
        end

      if MapSet.size(seen) == x, do: {:halt, k}, else: {:cont, seen}
    end)
    |> case do
      k when is_integer(k) -> k
      _ -> -1
    end
  end
end