Elixir Challenge

gistfile1.exs

defmodule Challenge do
 def resolve(stocks,target) do
    map = build_map(stocks, target)
    
    count_matching(stocks, map)
  end
  
  defp build_map(stocks, target) do
    Enum.reduce(stocks, %{}, fn stock, acc ->
      Map.put(acc, (stock - target) * -1, true)
    end)
  end

  defp count_matching(stocks, map) do
    Enum.filter(stocks, fn stock -> Map.get(map, stock) end)
    |> Enum.uniq()
    |> Enum.count()
  end
end 

stocks = [5, 6, 9, 13, 11, 6, 6, 3, 3]
target = 12

IO.puts Challenge.resolve(stocks, target)