Question

For two days I have been researching for this and have not found anything so I decided to write my own string repetition detector. Basically the function

def findRepetitions (string):

would receive a string and search for any repetitions; returns a list of strings reduced to their simplest form.

For a sample, it’d be:

findRepetitions ("trololololo") --> ["olo"]
findRepetitions ("bookkeeper") ---> ["o", "k", "e"]
findRepetitions ("Hello, Molly") -> ["l", "l"]
findRepetitions ("abcdefgh") -----> []
findRepetitions ("102102102") ----> ["102"]

In the third example, the function returns [“l”, “l”] instead of [“ll”], because I want to search for repetitions only in the neighboring characters.

I know that this may be hard, but I’ve been literally thinking over this for a long time and cannot find any smart solution to this.

Answer 1

Your examples are inconsistent. For example, olo does not repeat, like the l in Hello, Molly, in `trololololo; there’s an l between instances. Sequential repeats in trololololo are lolo, lo, olol, and ol. Are you asking for a ‘greedy’ algorithm? So, given trololololo, it would return olol?

In any case, here’s a bit of code.

from collections import Counter

def find_repetition(p):
    """ Returns a lookup dictionary for repetitions. """ 
    lookup = Counter()
    while len(p) != 0:
        for i in xrange(len(p)):
            lookup[p[0:i]] += 1
        p = p[1:]
    return lookup

def repeats(p):
    a = find_repetition(p)
    rs = [i for i in a if a[i] > 1][1:]
    return [r for r in rs if r*2 in p]

If you want it to be ‘greedy’ like I described, you have to add in another function that takes the results from repeats and chomps away at your string when it finds a match.

For now, the results look like this:

test = "trololololo", "bookkeeper", "Hello, Molly", "abcdefgh", "102102102"

>>> for i in test:
>>>     repeats(i)

['lolo', 'lo', 'olol', 'ol']
['e', 'o', 'k']
['l']
[]
['210', '021', '102']

warning

find_repetition is not very quick, since it basically generates all length combinations of the string and throws them into a Counter object.