Rep-string

Given a series of ones and zeroes in a string, define a repeated string or rep-string as a string which is created by repeating a substring of the first N characters of the string two or more times, truncated on the right to the length of the input string.

For example, the string '10011001100' is a rep-string as the leftmost four characters of '1001' are repeated three times and truncated on the right to give the original string.

The task is to:

Write a function/subroutine/method/... that takes a string and returns an indication of if it is a rep-string and the repeated string. (Either the string that is repeated, or the number of repeated characters would suffice).
Use the function to indicate the repeating substring if any, in the following

'1001110011'
'1110111011'
'0010010010'
'1010101010'
'1111111111'
'0100101101'
'0100100'
'101'
'1'

Show your output on this page.

Perl 6

<lang perl6>for <1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 1> {

   .say;
   if /^ (.+) $0+ (.*$) <?{ $0.substr(0,$1.chars) eq $1 }> / {
       say ' ' x $0.chars, "$0\n";
   }
   else {
       say " (no repeat)\n";
   }

}</lang>

Output:

1001110011
     10011

1110111011
    1110

0010010010
   001

1010101010
    1010

1111111111
     11111

0100101101
 (no repeat)

0100100
   010

101
 (no repeat)

1
 (no repeat)

Python

Python: Procedural

<lang python>def is_repeated(text):

   'check if the first part of the string is repeated throughout the string'
   len_text = len(text)
   for rep_len in range(len_text // 2,  0, -1):
       reps = (len_text + rep_len) // rep_len
       if (text[:rep_len] * reps).startswith(text):
           return rep_len  # equivalent to boolean True as will not be zero
   return 0     # equivalent to boolean False

matchstr = """\ 1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 1 """ for line in matchstr.split():

   ln = is_repeated(line)
   print('%r has a repetition length of %i i.e. %s' 
          % (line, ln, repr(line[:ln]) if ln else '*not* a repeated string'))</lang>

Output:

'1001110011' has a repetition length of 5 i.e. '10011'
'1110111011' has a repetition length of 4 i.e. '1110'
'0010010010' has a repetition length of 3 i.e. '001'
'1010101010' has a repetition length of 4 i.e. '1010'
'1111111111' has a repetition length of 5 i.e. '11111'
'0100101101' has a repetition length of 0 i.e. *not* a repeated string
'0100100' has a repetition length of 3 i.e. '010'
'101' has a repetition length of 0 i.e. *not* a repeated string
'1' has a repetition length of 0 i.e. *not* a repeated string

Python: Regexp

This version, inspired by the Perl 6 entry uses the regexp substitute where what the match is substituted with is returned by a function. <lang python>import re

matchstr = """\ 1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 1"""

def _checker(matchobj):

   g0, (g1, g2, g3, g4) = matchobj.group(0), matchobj.groups()
   if not g4 and g1 and g1.startswith(g3):
       return '%r repeats %r' % (g0, g1)
   return '%r is not a repeated string' % (g0,)

def checkit(txt):

   print(re.sub(r'(.+)(\1+)(.*)|(.*)', _checker, txt))

checkit(matchstr)</lang>

Output:

'1001110011' repeats '10011'
'1110111011' repeats '1110'
'0010010010' repeats '001'
'1010101010' repeats '1010'
'1111111111' repeats '11111'
'0100101101' is not a repeated string
'0100100' repeats '010'
'101' is not a repeated string
'1' is not a repeated string

REXX

<lang rexx>/* REXX ***************************************************************

11.05.2013 Walter Pachl
- - - - /

Call repstring '1001110011' Call repstring '1110111011' Call repstring '0010010010' Call repstring '1010101010' Call repstring '1111111111' Call repstring '0100101101' Call repstring '0100100' Call repstring '101' Call repstring '1' Exit

repstring: Parse Arg s sq='s' n=length(s) Do l=length(s)%2 to 1 By -1

 If substr(s,l+1,l)=left(s,l) Then Leave
 End

If l>0 Then Do

 rep_str=left(s,l)
 Do i=1 By 1
   If substr(s,i*l+1,l)<>rep_str Then
     Leave
   End
 If left(copies(rep_str,n),length(s))=s Then
   Say sq 'has a repetition length of' length(rep_str),
                                                'i.e.' 'rep_str'
 Else
   Say sq 'is not a repeated string'
 End

Else

 Say sq 'is not a repeated string'

Return</lang> Output:

'1001110011' has a repetition length of 5 i.e. '10011'
'1110111011' has a repetition length of 4 i.e. '1110'
'0010010010' has a repetition length of 3 i.e. '001'
'1010101010' has a repetition length of 4 i.e. '1010'
'1111111111' has a repetition length of 5 i.e. '11111'
'0100101101' is not a repeated string
'0100100' has a repetition length of 3 i.e. '010'
'101' is not a repeated string
'1' is not a repeated string