def subarray_sum arr, sum
  if arr.size == 1 && arr.first == sum
    return [0]
  end

  i = 0
  j = 1
  current_sum = arr[i]

  while j < arr.length
    current_sum += arr[j]
    j += 1

    while current_sum > sum && i < j-1
      current_sum -= arr[i]
      i += 1
    end

    if current_sum == sum
      return (i...j).to_a
    end
  end

  'No subarray found'
end