Grindr Interview Question

combine_interval.exs

defmodule CombineInterval do
  def merge_interval([]), do: []

  def merge_interval([h | t]), do: merge_interval(t, [h])

  def merge_interval([], acc), do: Enum.reverse(acc)

  def merge_interval([h | t], acc = [acc_h | acc_t]) do
    {start, _leng} = h
    {acc_h_start, acc_h_leng} = acc_h

    cond do
      end_pos(acc_h) < start -> merge_interval(t, [h | acc])
      acc_h_start <= start and end_pos(h) <= end_pos(acc_h) -> merge_interval(t, acc)
      acc_h_start <= start and end_pos(h) > end_pos(acc_h) ->
        leng_diff = end_pos(h) - end_pos(acc_h)
        merge_interval(t, [{acc_h_start, acc_h_leng + leng_diff} | acc_t])
    end
  end

  defp end_pos({start, leng}), do: start + leng
end

data = [{1, 3}, {2, 4}, {6, 1}, {10, 4}]
# result [{1, 6}, {10, 4}]
# assume data has been sorted
# execute with `elixir combine_interval.exs`

CombineInterval.merge_interval(data)
|> IO.inspect(label: "result")