bug report for radix sort

[InnoFang]

Description

if the test case for radix_sort.py is [104, 203, 308, 401], the result would be [401, 203, 104, 308]

It's wrong!

The reason is that if the digit_number is always 0 in one loop, it will exit the loop. In other words, If the same digit of all numbers is 0, then the result may be wrong. The similar example like:
Input: [2018, 33017, 24016]
Output: [24016, 33017, 2018]
Wrong again!!

Suggestion

Do not use is_done as a loop variable because the value of is_done is related to digit_number.

I think that by finding the maximum value of the array and assigning it to max_digit, using another variable digit with an initial value of 1 as the loop variable, each loop digit is multiplied by 10, and exit the loops when the digit greater than max_digit, which can guarantee the correct number of loops.

And the complexity will be O(nk + n) . n is the size of input list and k is the digit length of the number.

[InnoFang]

This issue had been solved, see #397