在已知字符串中出现N次的情况下，查找在字符串中重复哪个术语

Question

There is any way to do the following, without using brute force or something like that?

str = "abbcccddddefefef"
N = 3
repeated_term = func(str,N)

print(repeated_term )
> ['c','ef']


N = 2
term = func(str,N)

print(term)   
> ['b', 'dd', 'fe']    # Thanks to @blhsing for the correction!

and so on...

Answer 1

You can install the PyPi regex module , which supports variable-width lookbehind patterns, to use a regex that finds sequences that are repeated exactly N - 1 times:

import regex
def func(s, N):
    return regex.findall(r'(?=(.+?)(?:\1){%d}(?!\1))(?<!\1)' % (N - 1), s)

so that:

func("abbcccddddefefef", 3)

returns:

['c', 'ef']

and that:

func("abbcccddddefefef", 2)

returns:

['b', 'dd', 'fe']

Note that your expected output for N=2 is incorrect because 'dd' and 'fe' both also occur exactly 2 times.