How to compute very large numbers without a list

Question

I am trying to complete a coding challenge which requires me to count all of the digits between 1 and X, where can reach up to 400,000,000,000,000,000

My approach was to iterate over a list and add the amount of digits to my result in the end, like so:

def page_digits(pages):
    list_of_pages = list(range(1, pages + 1))
    res = 0
    for num in list_of_pages:
        res += len((str(num)))
    return res

but obviously creating a list of every digit between 1 and that big number requires a lot of storage and running this returns 'MemoryError Line 2'

How else could I go about this? or Avoid the problem

Answer 1

您没有理由需要将范围转换为列表。

>>> def page_digits(pages):
...     res = 0
...     for num in range(1, pages + 1):
...         res += len(str(num))
...     return res
...
>>> page_digits(100000)
488895

调用list构造函数会强制将范围中的每个元素单独存储在内存中，但常规range对象非常节省内存（它只包含您在构造时传递给它的参数），同时仍然是可迭代的。

您可能需要将范围转换为列表的唯一原因是更改其中的各个元素（您不能对范围执行此操作）。