Thanks in advance. I have a string:
A = 'asdfghjklmn'
How can I get a substring having a maximum length which is a multiple of three?
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You must elaborate what "multiple of three" means. Some examples would be useful.Adam Matan– Adam Matan2009-10-14 16:56:09 +00:00Commented Oct 14, 2009 at 16:56
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the question is rather vague. Are you looking for a substring that's as long as possible while satisfying the restraint or simply any substring which is a multiple of 3?AlbertoPL– AlbertoPL2009-10-14 16:57:03 +00:00Commented Oct 14, 2009 at 16:57
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5 Answers
You can use slice notation and integer arithmetic.
>>> a = 'asdfghjklmn'
>>> a[:len(a)//3*3]
'asdfghjkl'
>>> len(a)
11
>>> len(a[:len(a)//3*3])
9
In general, n//k*k will yield the largest multiple of k less than or equal to n.
It seems like you're looking for something like this:
>>> A = 'asdfghjklmn'
>>> mult, _ = divmod(len(A), 3)
>>> A[:mult*3]
'asdfghjkl'
here resulting string will have length which is multiple of three and it will be the longest possible substring of A with such length.
Comments
Yet another example:
>>> A = '12345678'
>>> A[:len(A) - len(A)%3]
'123456'
>>>
answered Oct 14, 2009 at 17:06
Nick Dandoulakis
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Comments
Is this what you want?
A = 'asdfghjklmn'
A[0:(len(A)/3)*3]
'asdfghjkl'
1 Comment
Oren S
does not run on python3: Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: slice indices must be integers or None or have an index method. You should have used floor division (just as Stephan202 did). See python.org/dev/peps/pep-0238
With the foreword that it will never be as efficient as the ones that actually use math to find the longest multiple-of-3-substring, here's a way to do it using regular expressions:
>>> re.findall("^(?:.{3})*", "asdfghjklmn")[0]
'asdfghjkl'
Changing the 3 quantifier will allow you to get different multiples.
