Rep-string

Rep-string is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

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: Proceedural

<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