How to generate this permutation?-CodePudding

This is the numeric permutation I would like to generate --> 1,12,21,123,132,213,... 987654321. I've made so many attempts but honestly I don't know where to start. I've tried using for loops, lists and permutations but it didn't work. So I've tried this:

from itertools import permutations
list = [1,2,3,4,5,6,7,8,9]
for x in list:
    permutations(list,x)
    list2 = list(permutations(list))
    print(list2)

The problem is not how to generate the permutation but to manage the increment of the digits.

Best regards and thank you all!

CodePudding user response：

Note that itertools.permutations returns permutations of all the same length (controlled by the r parameter, or the length of the iterable if r is None.) Based on that, the key is to recognize that what you are actually looking for is the union of multiple sets of permutations.

Here's one way we could get that:

from itertools import permutations
digits = [1,2,3,4,5,6,7,8,9]
result = []
for result_size in range(1, len(digits)   1):
    digits_slice = digits[:result_size]
    result.extend(permutations(digits_slice))
print(result)
# [(1,), (1, 2), (2, 1), (1, 2, 3), (1, 3, 2), (2, 1, 3), (2, 3, 1), (3, 1, 2), (3, 2, 1), (1, 2, 3, 4), (1, 2, 4, 3), ...]

Note: You should never use list as a variable name, because it shadows the built-in list type. I renamed list to digits to avoid this problem.

If you want the items in the result list to be ints instead of tuples, you can add:

result = [int(''.join(str(i) for i in tup)) for tup in result]
print(result)
# [1, 12, 21, 123, 132, 213, 231, 312, 321, 1234, 1243, ...]

CodePudding user response：

Try not to shadow python keywords. You could try something like this:

from itertools import permutations
lst = [str(i) for i in range(10)]

for i in range(1,len(lst) 1):
    sub_list = lst[0:i]
    g = ("".join(perm) for perm in permutations(sub_list))
    # print(list(g))

Feel free to uncomment the print statement.