Next Biggest Number Same Digits

Question

I don't see anything wrong with my code but I can't seem to return -1 when the input cannot produce a next bigger number, i.e. input of 531 which is descending.

import itertools as it
def next_bigger(n):
    if sorted("531", reverse = True) == list("531"):
        return -1
    s = tuple(str(n))
    for x in it.dropwhile(lambda x: x <= s, it.permutations(sorted(s))):
        return int(''.join(x))
    return s

Can someone please help?

Have you tried anything to achieve what you want so far? It's much better for you to have a go and show your efforts; questions that don't do this are usually poorly received here. — Aurora0001, Oct 10 '16 at 15:53
`if True:` will _always_ be True. What condition do you really want to check? — John Gordon, Oct 10 '16 at 16:02

score 2 · Answer 1 · answered Oct 10 '16 at 16:02

2

You can simply use an if statement at the beginning of your function to test whether the number is already in reverse sorted order. If it is sorted return -1 straight away:

>>> sorted("531", reverse = True) == list("531")
True

answered Oct 10 '16 at 16:02

Chris_Rands

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at what line would i place this conditional statement? – Mr. Jibz Oct 10 '16 at 16:06
@Mr.Jibz the first line after you define the function – Chris_Rands Oct 10 '16 at 16:10
when i do that (which is in edited code above), output reads "-1 should equal 21," 21 being the first test output with an input of 12. – Mr. Jibz Oct 10 '16 at 16:13
Well it needs to be `if sorted(str(n), reverse = True) == list(str(n)):`. you can't pass `531` every time of course – Chris_Rands Oct 10 '16 at 16:16
Don't use his literal example of "531". Use the actual input to the function. – John Gordon Oct 10 '16 at 16:17
makes sense, yes. now my problem is run time, ugh. – Mr. Jibz Oct 10 '16 at 16:29
"Process was terminated. It took longer than 8000ms to complete" – Mr. Jibz Oct 10 '16 at 16:29
Why are you calling `permutations()`? – John Gordon Oct 10 '16 at 16:54
my logic was that it would generate permutations of the same digits in order, which returning the first permutation that is greater than the input – Mr. Jibz Oct 10 '16 at 17:20
@Mr.Jibz Brute force approach is not the best, see http://stackoverflow.com/questions/9368205/given-a-number-find-the-next-higher-number-which-has-the-exact-same-set-of-digi and http://codereview.stackexchange.com/questions/115609/next-bigger-number-with-the-same-digits – Chris_Rands Oct 10 '16 at 18:11
Would it work to start by permuting only a few rightmost digits instead of the whole number? – John Gordon Oct 10 '16 at 18:20

Next Biggest Number Same Digits

1 Answers1