Question

I’m trying to make an easy script in Python which takes a number and saves in a variable, sorting the digits in ascending and descending orders and saving both in separate variables. Implementing Kaprekar’s constant.

It’s probably a pretty noobish question. But I’m new to this and I couldn’t find anything on Google that could help me. A site I found tried to explain a way using lists, but it didn’t work out very well.

Answer 1

Sort the digits in ascending and descending orders:

ascending = "".join(sorted(str(number)))

descending = "".join(sorted(str(number), reverse=True))

Like this:

>>> number = 5896
>>> ascending = "".join(sorted(str(number)))
>>>
>>> descending = "".join(sorted(str(number), reverse=True))
>>> ascending
'5689'
>>> descending
'9865'

And if you need them to be numbers again (not just strings), call int() on them:

>>> int(ascending)
5689
>>> int(descending)
9865

---

2020-01-30

>>> def kaprekar(number):
...     diff = None
...     while diff != 0:
...         ascending = "".join(sorted(str(number)))
...         descending = "".join(sorted(str(number), reverse=True))
...         print(ascending, descending)
...         next_number = int(descending) - int(ascending)
...         diff = number - next_number
...         number = next_number
...
>>> kaprekar(2777)
2777 7772
4599 9954
3555 5553
1899 9981
0288 8820
2358 8532
1467 7641