CodeWars/5kyu/best_travel/solution.rb

def choose_best_sum(t, k, ls)
  def choose_best_sum_rec(max_total_distance, n, distances)
    if n == 0 && max_total_distance >= 0 then
      return 0
    elsif max_total_distance < 0 || distances.size < 1 then
      return nil
    end

    found = Array.new(2)

    travelled = distances.pop
    including_last = choose_best_sum_rec(max_total_distance - travelled, n - 1, distances)
    if including_last != nil then
      found[0] = including_last + travelled
    end

    found[1] = choose_best_sum_rec(max_total_distance, n, distances)
    distances.push(travelled)

    return found.select { |x| x != nil }.max
  end

  choose_best_sum_rec(t, k, ls.sort)
end