defmodule BinaryStringGroups do
  def count(string) do
    string
    |> split()
    |> reduce()
  end

  defp split(string) do
    String.graphemes(string)
  end

  defp reduce(list) do
    [last: last_char, count: last_count, result: final_result] = Enum.reduce(list, [], fn
      ("1", []) -> [last: "1", count: 1, result: []]
      ("0", []) -> [last: "0", count: 1, result: []]
      ("1", [last: "1", count: count, result: result]) -> [last: "1", count: count + 1, result: result]
      ("1", [last: "0", count: count, result: result]) -> [last: "1", count: 1, result: [{"0", count} | result]]
      ("0", [last: "1", count: count, result: result]) -> [last: "0", count: 1, result: [{"1", count} | result]]
      ("0", [last: "0", count: count, result: result]) -> [last: "0", count: count + 1, result: result]
    end)

    [{last_char, last_count} | final_result]
  end
end

out = BinaryStringGroups.count("11010111011")
      |> Enum.max_by(fn ({_char, count}) -> count end)

IO.inspect out