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This means it might contain formatting issues, incorrect code, conceptual problems, or other severe issues.

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{{task}} 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 ''truncated on the right to the length of the input string, and in which the substring appears repeated at least twice in the original''.

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.

Note that the requirement for having the repeat occur two or more times means that the repeating unit is ''never'' longer than half the length of the input string.

• 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).
• There may be multiple sub-strings that make a string a rep-string - in that case an indication of all, or the longest, or the shortest would suffice.
• Use the function to indicate the repeating substring if any, in the following:
```
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1

```

```with Ada.Command_Line, Ada.Text_IO, Ada.Strings.Fixed;

procedure Rep_String is

function Find_Largest_Rep_String(S:String) return String is
L: Natural := S'Length;
begin
for I in reverse 1 .. L/2 loop
declare
T: String := S(S'First .. S'First + I-1); -- the first I characters of S
U: String := (1+(L/I)) * T; -- repeat T so often that U'Length >= L
begin -- compare first L characers of U with S
if U(U'First .. U'First + S'Length -1) = S then
return T; -- T is a rep-string
end if;
end;
end loop;
return ""; -- no rep string;
end Find_Largest_Rep_String;

Y: String := Find_Largest_Rep_String(X);

begin
if Y="" then
Ada.Text_IO.Put_Line("No rep-string for """ & X & """");
else
Ada.Text_IO.Put_Line("Longest rep-string for """& X &""": """& Y &"""");
end if;
end Rep_String;
```

{{out}}

```> ./rep_string 1001110011
Longest rep-string for "1001110011": "10011"
> ./rep_string 1110111011
Longest rep-string for "1110111011": "1110"
> ./rep_string 0010010010
Longest rep-string for "0010010010": "001"
> ./rep_string 1010101010
Longest rep-string for "1010101010": "1010"
> ./rep_string 1111111111
Longest rep-string for "1111111111": "11111"
> ./rep_string 0100101101
No rep-string for "0100101101"
> ./rep_string 0100100
Longest rep-string for "0100100": "010"
> ./rep_string 101
No rep-string for "101"
> ./rep_string 11
Longest rep-string for "11": "1"
> ./rep_string 00
Longest rep-string for "00": "0"
> ./rep_string 1
No rep-string for "1"
```

## ALGOL 68

{{works with|ALGOL 68G|Any - tested with release 2.8.win32}}

```# procedure to find the longest rep-string in a given string               #
# the input string is not validated to contain only "0" and "1" characters #
PROC longest rep string = ( STRING input )STRING:
BEGIN

STRING result           := "";

# ensure the string we are working on has a lower-bound of 1           #
STRING str               = input[ AT 1 ];

# work backwards from half the input string looking for a rep-string   #
FOR string length FROM UPB str OVER 2 BY -1 TO 1
WHILE
STRING left substring  = str[ 1 : string length ];
# if the left substgring repeated a sufficient number of times     #
# (truncated on the right) is equal to the original string, then   #
# we have found the longest rep-string                             #
STRING repeated string = ( left substring
* ( ( UPB str OVER string length ) + 1 )
)[ 1 : UPB str ];
IF str = repeated string
THEN
# found a rep-string                                           #
result := left substring;
FALSE
ELSE
# not a rep-string, keep looking                               #
TRUE
FI
DO
SKIP
OD;

result
END; # longest rep string #

# test the longest rep string procedure                                    #
main:
(

[]STRING tests = ( "1001110011"
, "1110111011"
, "0010010010"
, "1010101010"
, "1111111111"
, "0100101101"
, "0100100"
, "101"
, "11"
, "00"
, "1"
);

FOR test number FROM LWB tests TO UPB tests
DO
STRING rep string = longest rep string( tests[ test number ] );
print( ( tests[ test number ]
, ": "
, IF rep string = ""
THEN "no rep string"
ELSE "longest rep string: """ + rep string + """"
FI
, newline
)
)
OD
)
```

{{out}}

```1001110011: longest rep string: "10011"
1110111011: longest rep string: "1110"
0010010010: longest rep string: "001"
1010101010: longest rep string: "1010"
1111111111: longest rep string: "11111"
0100101101: no rep string
0100100: longest rep string: "010"
101: no rep string
11: longest rep string: "1"
00: longest rep string: "0"
1: no rep string
```

## AppleScript

```-- REP-CYCLES ----------------------------------------------------------------

-- repCycles :: String -> [String]
on repCycles(xs)
set n to length of xs

script isCycle
on |λ|(cs)
xs = takeCycle(n, cs)
end |λ|
end script

filter(isCycle, tail(inits(take(quot(n, 2), xs))))
end repCycles

-- cycleReport :: String -> [String]
on cycleReport(xs)
set reps to repCycles(xs)

if isNull(reps) then
{xs, "(n/a)"}
else
{xs, |last|(reps)}
end if
end cycleReport

-- TEST ----------------------------------------------------------------------
on run
set samples to {"1001110011", "1110111011", "0010010010", ¬
"1010101010", "1111111111", "0100101101", "0100100", ¬
"101", "11", "00", "1"}

unlines(cons("Longest cycle:" & linefeed, ¬
map(curry(intercalate)'s |λ|(" -> "), ¬
map(cycleReport, samples))))

end run

-- GENERIC FUNCTIONS ---------------------------------------------------------

-- concat :: [[a]] -> [a] | [String] -> String
on concat(xs)
if length of xs > 0 and class of (item 1 of xs) is string then
set acc to ""
else
set acc to {}
end if
repeat with i from 1 to length of xs
set acc to acc & item i of xs
end repeat
acc
end concat

-- cons :: a -> [a] -> [a]
on cons(x, xs)
{x} & xs
end cons

-- curry :: (Script|Handler) -> Script
on curry(f)
script
on |λ|(a)
script
on |λ|(b)
|λ|(a, b) of mReturn(f)
end |λ|
end script
end |λ|
end script
end curry

-- filter :: (a -> Bool) -> [a] -> [a]
on filter(f, xs)
tell mReturn(f)
set lst to {}
set lng to length of xs
repeat with i from 1 to lng
set v to item i of xs
if |λ|(v, i, xs) then set end of lst to v
end repeat
return lst
end tell
end filter

-- foldl :: (a -> b -> a) -> a -> [b] -> a
on foldl(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from 1 to lng
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldl

-- inits :: [a] -> [[a]]
-- inits :: String -> [String]
on inits(xs)
script elemInit
on |λ|(_, i, xs)
items 1 thru i of xs
end |λ|
end script

script charInit
on |λ|(_, i, xs)
text 1 thru i of xs
end |λ|
end script

if class of xs is string then
{""} & map(charInit, xs)
else
{{}} & map(elemInit, xs)
end if
end inits

-- intercalate :: Text -> [Text] -> Text
on intercalate(strText, lstText)
set {dlm, my text item delimiters} to {my text item delimiters, strText}
set strJoined to lstText as text
set my text item delimiters to dlm
return strJoined
end intercalate

-- last :: [a] -> a
on |last|(xs)
if length of xs > 0 then
item -1 of xs
else
missing value
end if
end |last|

-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map

-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn

-- isNull :: [a] -> Bool
on isNull(xs)
xs = {}
end isNull

-- min :: Ord a => a -> a -> a
on min(x, y)
if y < x then
y
else
x
end if
end min

-- quot :: Integral a => a -> a -> a
on quot(n, m)
n div m
end quot

-- replicate :: Int -> a -> [a]
on replicate(n, a)
set out to {}
if n < 1 then return out
set dbl to {a}

repeat while (n > 1)
if (n mod 2) > 0 then set out to out & dbl
set n to (n div 2)
set dbl to (dbl & dbl)
end repeat
return out & dbl
end replicate

-- tail :: [a] -> [a]
on tail(xs)
if length of xs > 1 then
items 2 thru -1 of xs
else
{}
end if
end tail

-- take :: Int -> [a] -> [a]
on take(n, xs)
if class of xs is string then
if n > 0 then
text 1 thru min(n, length of xs) of xs
else
""
end if
else
if n > 0 then
items 1 thru min(n, length of xs) of xs
else
{}
end if
end if
end take

-- takeCycle :: Int -> [a] -> [a]
on takeCycle(n, xs)
set lng to length of xs
if lng ≥ n then
set cycle to xs
else
set cycle to concat(replicate((n div lng) + 1, xs))
end if

if class of xs is string then
items 1 thru n of cycle as string
else
items 1 thru n of cycle
end if
end takeCycle

-- unlines :: [String] -> String
on unlines(xs)
intercalate(linefeed, xs)
end unlines
```

{{Out}}

```Longest cycle:

1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 1010
1111111111 -> 11111
0100101101 -> (n/a)
0100100 -> 010
101 -> (n/a)
11 -> 1
00 -> 0
1 -> (n/a)
```

## AutoHotkey

{{works with|AutoHotkey 1.1}}

```In := ["1001110011", "1110111011", "0010010010", "1010101010"
, "1111111111", "0100101101", "0100100", "101", "11", "00", "1"]
for k, v in In
Out .= RepString(v) "`t" v "`n"
MsgBox, % Out

RepString(s) {
Loop, % StrLen(s) // 2 {
i := A_Index
Loop, Parse, s
{
pos := Mod(A_Index, i)
if (A_LoopField != SubStr(s, !pos ? i : pos, 1))
continue, 2
}
return SubStr(s, 1, i)
}
return "N/A"
}
```

{{Out}}

```10011	1001110011
1110	1110111011
001	0010010010
10	1010101010
1	1111111111
N/A	0100101101
010	0100100
N/A	101
1	11
0	00
N/A	1
```

## BaCon

```all\$ = "1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 00 1"

FOR word\$ IN all\$
FOR x = LEN(word\$)/2 DOWNTO 1

ex\$ = EXPLODE\$(word\$, x)

FOR st\$ IN UNIQ\$(ex\$)
IF NOT(REGEX(HEAD\$(ex\$, 1), "^" & st\$)) THEN CONTINUE 2
NEXT

PRINT "Repeating string: ", word\$, " -> ", HEAD\$(ex\$, 1)
CONTINUE 2
NEXT

PRINT "Not a repeating string: ", word\$
NEXT
```

{{out}}

```
Repeating string: 1001110011 -> 10011
Repeating string: 1110111011 -> 1110
Repeating string: 0010010010 -> 001
Repeating string: 1010101010 -> 1010
Repeating string: 1111111111 -> 11111
Not a repeating string: 0100101101
Repeating string: 0100100 -> 010
Not a repeating string: 101
Repeating string: 11 -> 1
Repeating string: 00 -> 0
Not a repeating string: 1

```

## Bracmat

```( ( rep-string
=   reps L x y
.   ( reps
=   x y z
.   !arg:(?x.?y)
& ( @(!y:!x ?z)&reps\$(!x.!z)
| @(!x:!y ?)
)
)
& (   :?L
& @( !arg
:   %?x
!x
( ?y
& reps\$(!x.!y)
& !x !L:?L
& ~
)
)
|   !L:
& out\$(str\$(!arg " is not a rep-string"))
| out\$(!arg ":" !L)
)
)
& rep-string\$1001110011
& rep-string\$1110111011
& rep-string\$0010010010
& rep-string\$1010101010
& rep-string\$1111111111
& rep-string\$0100101101
& rep-string\$0100100
& rep-string\$101
& rep-string\$11
& rep-string\$00
& rep-string\$1
);
```

{{Out}}

```1001110011 : 10011
1110111011 : 1110
0010010010 : 001
1010101010 : 1010 10
1111111111 : 11111 1111 111 11 1
0100101101 is not a rep-string
0100100 : 010
101 is not a rep-string
11 : 1
00 : 0
1 is not a rep-string
```

## C

### Longest substring

```
#include <stdio.h>
#include <string.h>

int repstr(char *str)
{
if (!str) return 0;

size_t sl = strlen(str) / 2;
while (sl > 0) {
if (strstr(str, str + sl) == str)
return sl;
--sl;
}

return 0;
}

int main(void)
{
char *strs[] = { "1001110011", "1110111011", "0010010010", "1111111111",
"0100101101", "0100100", "101", "11", "00", "1" };

size_t strslen = sizeof(strs) / sizeof(strs[0]);
size_t i;
for (i = 0; i < strslen; ++i) {
int n = repstr(strs[i]);
if (n)
printf("\"%s\" = rep-string \"%.*s\"\n", strs[i], n, strs[i]);
else
printf("\"%s\" = not a rep-string\n", strs[i]);
}

return 0;
}

```

{{out}}

```
"1001110011" = rep-string "10011"
"1110111011" = rep-string "1110"
"0010010010" = rep-string "001"
"1111111111" = rep-string "11111"
"0100101101" = not a rep-string
"0100100" = rep-string "010"
"101" = not a rep-string
"11" = rep-string "1"
"00" = rep-string "0"
"1" = not a rep-string

```

### shortest substring

```
// strstr : Returns a pointer to the first occurrence of str2 in str1, or a null pointer if str2 is not part of str1.
// size_t is an unsigned integer typ
// lokks for the shortest substring
int repstr(char *str)
{
if (!str) return 0; // if empty input

size_t sl = 1;
size_t sl_max = strlen(str) ;

while (sl < sl_max) {
if (strstr(str, str + sl) == str) // How it works ???? It checks the whole string str
return sl;
++sl;
}

return 0;
}

```

## C++

```#include <string>
#include <vector>
#include <boost/regex.hpp>

bool is_repstring( const std::string & teststring , std::string & repunit ) {
std::string regex( "^(.+)\\1+(.*)\$" ) ;
boost::regex e ( regex ) ;
boost::smatch what ;
if ( boost::regex_match( teststring , what , e , boost::match_extra ) ) {
std::string firstbracket( what[1 ] ) ;
std::string secondbracket( what[ 2 ] ) ;
if ( firstbracket.length( ) >= secondbracket.length( ) &&
firstbracket.find( secondbracket ) != std::string::npos ) {
repunit = firstbracket  ;
}
}
return !repunit.empty( ) ;
}

int main( ) {
std::vector<std::string> teststrings { "1001110011" , "1110111011" , "0010010010" ,
"1010101010" , "1111111111" , "0100101101" , "0100100" , "101" , "11" , "00" , "1" } ;
std::string theRep ;
for ( std::string myString : teststrings ) {
if ( is_repstring( myString , theRep ) ) {
std::cout << myString << " is a rep string! Here is a repeating string:\n" ;
std::cout << theRep << " " ;
}
else {
std::cout << myString << " is no rep string!" ;
}
theRep.clear( ) ;
std::cout << std::endl ;
}
return 0 ;
}
```

{{out}}

```1001110011 is a rep string! Here is a repeating string:
10011
1110111011 is a rep string! Here is a repeating string:
1110
0010010010 is a rep string! Here is a repeating string:
001
1010101010 is a rep string! Here is a repeating string:
1010
1111111111 is a rep string! Here is a repeating string:
11111
0100101101 is no rep string!
0100100 is a rep string! Here is a repeating string:
010
101 is no rep string!
11 is a rep string! Here is a repeating string:
1
00 is a rep string! Here is a repeating string:
0
1 is no rep string!
```

## Common Lisp

```
(defun rep-stringv (a-str &optional (max-rotation (floor (/ (length a-str) 2))))
;; Exit condition if no repetition found.
(cond ((< max-rotation 1) "Not a repeating string")
;; Two checks:
;; 1. Truncated string must be equal to rotation by repetion size.
;; 2. Remaining chars (rest-str) are identical to starting chars (beg-str)
((let* ((trunc (* max-rotation (truncate (length a-str) max-rotation)))
(truncated-str (subseq a-str 0 trunc))
(rest-str (subseq a-str trunc))
(beg-str (subseq a-str 0 (rem (length a-str) max-rotation))))
(and (string= beg-str rest-str)
(string= (alexandria:rotate (copy-seq truncated-str) max-rotation)
truncated-str)))
;; If both checks pass, return the repeting string.
(subseq a-str 0 max-rotation))
;; Recurse function reducing length of rotation.
(t (rep-stringv a-str (1- max-rotation)))))

```

{{out}}

```
(setf test-strings '("1001110011"
"1110111011"
"0010010010"
"1010101010"
"1111111111"
"0100101101"
"0100100"
"101"
"11"
"00"
"1"
))

(loop for item in test-strings
collecting (cons item (rep-stringv item)))

```
```
(("1001110011" . "10011") ("1110111011" . "1110") ("0010010010" . "001")
("1010101010" . "1010") ("1111111111" . "11111")
("0100101101" . "Not a repeating string") ("0100100" . "010")
("101" . "Not a repeating string") ("11" . "1") ("00" . "0")
("1" . "Not a repeating string"))

```

## D

Two different algorithms. The second is from the Perl 6 entry.

```import std.stdio, std.string, std.conv, std.range, std.algorithm,
std.ascii, std.typecons;

Nullable!(size_t, 0) repString1(in string s) pure nothrow @safe @nogc
in {
//assert(s.all!isASCII);
assert(s.representation.all!isASCII);
} body {
immutable sr = s.representation;
foreach_reverse (immutable n; 1 .. sr.length / 2 + 1)
if (sr.take(n).cycle.take(sr.length).equal(sr))
return typeof(return)(n);
return typeof(return)();
}

Nullable!(size_t, 0) repString2(in string s) pure @safe /*@nogc*/
in {
assert(s.countchars("01") == s.length);
} body {
immutable bits = s.to!ulong(2);

foreach_reverse (immutable left; 1 .. s.length / 2 + 1) {
immutable right = s.length - left;
if ((bits ^ (bits >> left)) == ((bits >> right) << right))
return typeof(return)(left);
}
return typeof(return)();
}

void main() {
immutable words = "1001110011 1110111011 0010010010 1010101010
1111111111 0100101101 0100100 101 11 00 1".split;

foreach (immutable w; words) {
immutable r1 = w.repString1;
//assert(r1 == w.repString2);
immutable r2 = w.repString2;
assert((r1.isNull && r2.isNull) || r1 == r2);
if (r1.isNull)
writeln(w, " (no repeat)");
else
writefln("%(%s %)", w.chunks(r1));
}
}
```

{{out}}

```10011 10011
1110 1110 11
001 001 001 0
1010 1010 10
11111 11111
0100101101 (no repeat)
010 010 0
101 (no repeat)
1 1
0 0
1 (no repeat)
```

## Dyalect

{{trans|Go}}

```func rep(s) {
var x = s.len() / 2
while x > 0 {
if s.startsWith(s.sub(x)) {
return x
}
x -= 1
}
return 0
}

const m = [
"1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"
]

for s in m {
if (rep(s) is n) && n > 0 {
print("\(s)  \(n) rep-string \(s.sub(n))")
} else {
print("\(s)  not a rep-string")
}
}
```

{{out}}

```1001110011  5 rep-string 10011
1110111011  4 rep-string 111011
0010010010  3 rep-string 0010010
1010101010  4 rep-string 101010
1111111111  5 rep-string 11111
0100101101  not a rep-string
0100100  3 rep-string 0100
101  not a rep-string
11  1 rep-string 1
00  1 rep-string 0
1  not a rep-string
```

## EchoLisp

```
(lib 'list) ;; list-rotate

;; a list is a rep-list if equal? to itself after a rotation of lam units
;; lam <= list length / 2
;; truncate to a multiple of lam before rotating
;; try cycles in decreasing lam order (longest wins)

(define (cyclic? cyclic)
(define len (length cyclic))
(define trunc null)

(if (> len 1)
(for ((lam (in-range (quotient len 2) 0 -1)))
(set! trunc (take cyclic (- len (modulo len lam))))
#:break (equal? trunc  (list-rotate trunc lam)) => (list->string (take cyclic lam))
'no-rep )
'too-short-no-rep))

```

{{out}}

```
(define strings '["1001110011" "1110111011" "0010010010" "1010101010"
"1111111111" "0100101101" "0100100" "101" "11" "00" "1"])

(for-each (lambda (s)
(writeln s (cyclic? (string->list s)))) strings))

"1001110011"     "10011"
"1110111011"     "1110"
"0010010010"     "001"
"1010101010"     "1010"
"1111111111"     "11111"
"0100101101"     no-rep
"0100100"     "010"
"101"     no-rep
"11"     "1"
"00"     "0"
"1"     too-short-no-rep

```

## Elixir

```defmodule Rep_string do
def find(""), do: IO.puts "String was empty (no repetition)"
def find(str) do
IO.puts str
rep_pos = Enum.find(div(String.length(str),2)..1, fn pos ->
String.starts_with?(str, String.slice(str, pos..-1))
end)
if rep_pos && rep_pos>0 do
IO.puts String.duplicate(" ", rep_pos) <> String.slice(str, 0, rep_pos)
else
IO.puts "(no repetition)"
end
IO.puts ""
end
end

strs = ~w(1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1)

Enum.each(strs, fn str -> Rep_string.find(str) end)
```

{{out}}

```
1001110011
10011

1110111011
1110

0010010010
001

1010101010
1010

1111111111
11111

0100101101
(no repetition)

0100100
010

101
(no repetition)

11
1

00
0

1
(no repetition)

```

```let isPrefix p (s : string) = s.StartsWith(p)
let getPrefix n (s : string) = s.Substring(0,n)

let repPrefixOf str =
let rec isRepeatedPrefix p s =
if isPrefix p s then isRepeatedPrefix p (s.Substring (p.Length))
else isPrefix s p

let rec getLongestRepeatedPrefix n =
if n = 0 then None
elif isRepeatedPrefix (getPrefix n str) str then Some(getPrefix n str)
else getLongestRepeatedPrefix (n-1)

getLongestRepeatedPrefix (str.Length/2)

[<EntryPoint>]
let main argv =
printfn "Testing for rep-string (and showing the longest repeated prefix in case):"
[
"1001110011"
"1110111011"
"0010010010"
"1010101010"
"1111111111"
"0100101101"
"0100100"
"101"
"11"
"00"
"1"
] |>
List.map (fun s ->
match repPrefixOf s with | None -> s + ": NO" | Some(p) -> s + ": YES ("+ p + ")")
|> List.iter (printfn "%s")
0
```

{{out}}

```Testing for rep-string (and showing the longest repeated prefix in case):
1001110011: YES (10011)
1110111011: YES (1110)
0010010010: YES (001)
1010101010: YES (1010)
1111111111: YES (11111)
0100101101: NO
0100100: YES (010)
101: NO
11: YES (1)
00: YES (0)
1: NO
```

## Factor

```USING: formatting grouping kernel math math.ranges qw sequences ;
IN: rosetta-code.rep-string

: (find-rep-string) ( str -- str )
dup dup length 2/ [1,b]
[ <groups> [ head? ] monotonic? ] with find nip dup
[ head ] [ 2drop "N/A" ] if ;

: find-rep-string ( str -- str )
dup length 1 <= [ drop "N/A" ] [ (find-rep-string) ] if ;

qw{ 1001110011 1110111011 0010010010 1010101010 1111111111
0100101101 0100100 101 11 00 1 }
"Shortest cycle:\n\n" printf
[ dup find-rep-string "%-10s -> %s\n" printf ] each
```

{{out}}

```
Shortest cycle:

1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 10
1111111111 -> 1
0100101101 -> N/A
0100100    -> 010
101        -> N/A
11         -> 1
00         -> 0
1          -> N/A

```

## Forth

{{trans|Python}} {{works with|GNU Forth}}

```: rep-string ( caddr1 u1 -- caddr2 u2 ) \ u2=0: not a rep-string
2dup dup >r  r@ 2/ /string
begin  2over 2over string-prefix? 0=  over r@ <  and  while  -1 /string  repeat
r> swap - >r  2drop  r> ;

: test ( caddr u -- )
2dup type ."  has "
rep-string ?dup 0= if drop ." no " else type ."  as " then
." repeating substring" cr ;
: tests
s" 1001110011" test
s" 1110111011" test
s" 0010010010" test
s" 1010101010" test
s" 1111111111" test
s" 0100101101" test
s" 0100100" test
s" 101" test
s" 11" test
s" 00" test
s" 1" test ;
```

{{out}}

```cr tests
1001110011 has 10011 as repeating substring
1110111011 has 1110 as repeating substring
0010010010 has 001 as repeating substring
1010101010 has 1010 as repeating substring
1111111111 has 11111 as repeating substring
0100101101 has no repeating substring
0100100 has 010 as repeating substring
101 has no repeating substring
11 has 1 as repeating substring
00 has 0 as repeating substring
1 has no repeating substring
ok
```

## Go

{{trans|Python}}

```package main

import (
"fmt"
"strings"
)

func rep(s string) int {
for x := len(s) / 2; x > 0; x-- {
if strings.HasPrefix(s, s[x:]) {
return x
}
}
return 0
}

const m = `
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1`

func main() {
for _, s := range strings.Fields(m) {
if n := rep(s); n > 0 {
fmt.Printf("%q  %d rep-string %q\n", s, n, s[:n])
} else {
fmt.Printf("%q  not a rep-string\n", s)
}
}
}
```

{{out}}

```
"1001110011"  5 rep-string "10011"
"1110111011"  4 rep-string "1110"
"0010010010"  3 rep-string "001"
"1010101010"  4 rep-string "1010"
"1111111111"  5 rep-string "11111"
"0100101101"  not a rep-string
"0100100"  3 rep-string "010"
"101"  not a rep-string
"11"  1 rep-string "1"
"00"  1 rep-string "0"
"1"  not a rep-string

```

```import Data.List (maximumBy, inits)

repstring :: String -> Maybe String
-- empty strings are not rep strings
repstring [] = Nothing
-- strings with only one character are not rep strings
repstring (_:[]) = Nothing
repstring xs
| any (`notElem` "01") xs = Nothing
| otherwise = longest xs
where
-- length of the original string
lxs = length xs
-- half that length
lq2 = lxs `quot` 2
-- make a string of same length using repetitions of a part
-- of the original string, and also return the substring used
subrepeat x = (x, take lxs \$ concat \$ repeat x)
-- check if a repeated string matches the original string
sndValid (_, ys) = ys == xs
-- make all possible strings out of repetitions of parts of
-- the original string, which have max. length lq2
possible = map subrepeat . take lq2 . tail . inits
-- filter only valid possibilities, and return the substrings
-- used for building them
valid = map fst . filter sndValid . possible
-- see which string is longer
compLength a b = compare (length a) (length b)
-- get the longest substring that, repeated, builds a string
-- that matches the original string
longest ys = case valid ys of
[] -> Nothing
zs -> Just \$ maximumBy compLength zs

main :: IO ()
main = do
mapM_ processIO examples
where
examples = ["1001110011", "1110111011", "0010010010",
"1010101010", "1111111111", "0100101101", "0100100",
"101", "11", "00", "1"]
process = maybe "Not a rep string" id . repstring
processIO xs = do
putStr (xs ++ ": ")
putStrLn \$ process xs
```

{{Out}}

```1001110011: 10011
1110111011: 1110
0010010010: 001
1010101010: 1010
1111111111: 11111
0100101101: Not a rep string
0100100: 010
101: Not a rep string
11: 1
00: 0
1: Not a rep string
```

Or, alternatively:

```import Data.List (inits, intercalate, transpose)
import Data.Bool (bool)

-- REP-CYCLES ---------------------------------------------
repCycles :: String -> [String]
repCycles cs =
let n = length cs
in filter ((cs ==) . take n . cycle) (tail \$ inits (take (quot n 2) cs))

-- TEST ---------------------------------------------------
main :: IO ()
main =
putStrLn \$
fTable
"Longest cycles:\n"
id
((flip bool "n/a" . last) <*> null)
repCycles
[ "1001110011"
, "1110111011"
, "0010010010"
, "1010101010"
, "1111111111"
, "0100101101"
, "0100100"
, "101"
, "11"
, "00"
, "1"
]

-- GENERIC ------------------------------------------------
fTable :: String -> (a -> String) -> (b -> String) -> (a -> b) -> [a] -> String
fTable s xShow fxShow f xs =
let rjust n c = drop . length <*> (replicate n c ++)
w = maximum (length . xShow <\$> xs)
in unlines \$
s : fmap (((++) . rjust w ' ' . xShow) <*> ((" -> " ++) . fxShow . f)) xs
```

{{Out}}

```Longest cycles:

1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 1010
1111111111 -> 11111
0100101101 -> n/a
0100100 -> 010
101 -> n/a
11 -> 1
00 -> 0
1 -> n/a
```

The following works in both languages.

```procedure main(A)
every write(s := !A,": ",(repString(s) | "Not a rep string!")\1)
end

procedure repString(s)
rs := s[1+:*s/2]
while (*rs > 0) & (s ~== lrepl(rs,*s,rs)) do rs := rs[1:-1]
return (*rs > 0, rs)
end

procedure lrepl(s1,n,s2)   # The standard left() procedure won't work.
while *s1 < n do s1 ||:= s2
return s1[1+:n]
end
```

{{Out}}

```
->rs 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 1
1110111011: 1110
0010010010: 001
1010101010: 1010
1111111111: 11111
0100101101: Not a rep string!
0100100: 010
101: Not a rep string!
11: 1
1: Not a rep string!
->

```

## J

Here's a test:

```:@i.@<.@-:@#
rep=: \$@] \$ \$

isRepStr=: +./@((] -: rep)"0 1~ replengths)
```

Example use:

```   isRepStr '1001110011'
1
Tests=: noun define
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1
)
isRepStr;._2 Tests     NB. run all tests
1 1 1 1 1 0 1 0 1 1 0
```

We could also report the lengths of the repeated prefix, though this seems more arbitrary:

```nRepStr=: 0 -.~ (([ * ] -: rep)"0 1~ replengths)
```

With the above examples:

```   ":@nRepStr;._2 Tests
5
4
3
2 4
1 2 3 4 5

3

1
1
```

Here, the "non-str-rep" cases are indicated by an empty list of prefix lengths.

## Java

```public class RepString {

static final String[] input = {"1001110011", "1110111011", "0010010010",
"1010101010", "1111111111", "0100101101", "0100100", "101", "11",
"00", "1", "0100101"};

public static void main(String[] args) {
for (String s : input)
System.out.printf("%s : %s%n", s, repString(s));
}

static String repString(String s) {
int len = s.length();
outer:
for (int part = len / 2; part > 0; part--) {
int tail = len % part;
if (tail > 0 && !s.substring(0, tail).equals(s.substring(len - tail)))
continue;
for (int j = 0; j < len / part - 1; j++) {
int a = j * part;
int b = (j + 1) * part;
int c = (j + 2) * part;
if (!s.substring(a, b).equals(s.substring(b, c)))
continue outer;
}
return s.substring(0, part);
}
return "none";
}
}
```

{{Out}}

```1001110011 : 10011
1110111011 : 1110
0010010010 : 001
1010101010 : 1010
1111111111 : 11111
0100101101 : none
0100100 : 010
101 : none
11 : 1
00 : 0
1 : none
0100101 : none
```

## JavaScript

### ES6

```(() => {
'use strict';

const main = () => {

// REP-CYCLES -------------------------------------

// repCycles :: String -> [String]
const repCycles = s => {
const n = s.length;
return filter(
x => s === take(n, cycle(x)).join(''),
tail(inits(take(quot(n, 2), s)))
);
};

// TEST -------------------------------------------
console.log(fTable(
'Longest cycles:\n',
str,
xs => 0 < xs.length ? concat(last(xs)) : '(none)',
repCycles,
[
'1001110011',
'1110111011',
'0010010010',
'1010101010',
'1111111111',
'0100101101',
'0100100',
'101',
'11',
'00',
'1'
]
));
};

// GENERIC FUNCTIONS ----------------------------------

// concat :: [[a]] -> [a]
// concat :: [String] -> String
const concat = xs =>
0 < xs.length ? (() => {
const unit = 'string' !== typeof xs[0] ? (
[]
) : '';
return unit.concat.apply(unit, xs);
})() : [];

// cycle :: [a] -> Generator [a]
function* cycle(xs) {
const lng = xs.length;
let i = 0;
while (true) {
yield(xs[i])
i = (1 + i) % lng;
}
}

// filter :: (a -> Bool) -> [a] -> [a]
const filter = (f, xs) => xs.filter(f);

// fTable :: String -> (a -> String) ->
//                     (b -> String) -> (a -> b) -> [a] -> String
const fTable = (s, xShow, fxShow, f, xs) => {
// Heading -> x display function ->
//           fx display function ->
//    f -> values -> tabular string
const
ys = xs.map(xShow),
w = Math.max(...ys.map(length));
return s + '\n' + zipWith(
(a, b) => a.padStart(w, ' ') + ' -> ' + b,
ys,
xs.map(x => fxShow(f(x)))
).join('\n');
};

// inits([1, 2, 3]) -> [[], [1], [1, 2], [1, 2, 3]
// inits('abc') -> ["", "a", "ab", "abc"]

// inits :: [a] -> [[a]]
// inits :: String -> [String]
const inits = xs => [
[]
]
.concat(('string' === typeof xs ? xs.split('') : xs)
.map((_, i, lst) => lst.slice(0, 1 + i)));

// last :: [a] -> a
const last = xs =>
0 < xs.length ? xs.slice(-1)[0] : undefined;

// Returns Infinity over objects without finite length.
// This enables zip and zipWith to choose the shorter
// argument when one is non-finite, like cycle, repeat etc

// length :: [a] -> Int
const length = xs =>
(Array.isArray(xs) || 'string' === typeof xs) ? (
xs.length
) : Infinity;

// quot :: Int -> Int -> Int
const quot = (n, m) => Math.floor(n / m);

// str :: a -> String
const str = x => x.toString();

// tail :: [a] -> [a]
const tail = xs => 0 < xs.length ? xs.slice(1) : [];

// take :: Int -> [a] -> [a]
// take :: Int -> String -> String
const take = (n, xs) =>
'GeneratorFunction' !== xs.constructor.constructor.name ? (
xs.slice(0, n)
) : [].concat.apply([], Array.from({
length: n
}, () => {
const x = xs.next();
return x.done ? [] : [x.value];
}));

// unlines :: [String] -> String
const unlines = xs => xs.join('\n');

// Use of `take` and `length` here allows zipping with non-finite lists
// i.e. generators like cycle, repeat, iterate.

// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
const zipWith = (f, xs, ys) => {
const
lng = Math.min(length(xs), length(ys)),
as = take(lng, xs),
bs = take(lng, ys);
return Array.from({
length: lng
}, (_, i) => f(as[i], bs[i], i));
};

// MAIN ---
return main();
})();
```

{{Out}}

```Longest cycles:

1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 1010
1111111111 -> 11111
0100101101 -> (none)
0100100 -> 010
101 -> (none)
11 -> 1
00 -> 0
1 -> (none)
```

## jq

For each test string, a JSON object giving details about the prefixes that satisfy the requirement is presented; if the string is not a rep-string, the empty array ([]) is shown.

```def is_rep_string:
# if self is a rep-string then return [n, prefix]
# where n is the number of full occurrences of prefix
def _check(prefix; n; sofar):
length as \$length
| if length <= (sofar|length) then [n, prefix]
else (sofar+prefix) as \$sofar
| if  startswith(\$sofar) then _check(prefix; n+1; \$sofar)
elif (\$sofar|length) > \$length and
startswith(\$sofar[0:\$length]) then [n, prefix]
else [0, prefix]
end
end
;

[range (1; length/2 + 1) as \$i
| .[0:\$i] as \$prefix
| _check(\$prefix; 1; \$prefix)
| select( .[0] > 1 ) ]
;

```

'''Example''':

```def test:
(
"1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"
) | { (.) : is_rep_string }
;

test
```

{{Out}}

``` \$ jq -n -c -f rep-string.jq
{"1001110011":[[2,"10011"]]}
{"1110111011":[[2,"1110"]]}
{"0010010010":[[3,"001"]]}
{"1010101010":[[5,"10"],[2,"1010"]]}
{"1111111111":[[10,"1"],[5,"11"],[3,"111"],[2,"1111"],[2,"11111"]]}
{"0100101101":[]}
{"0100100":[[2,"010"]]}
{"101":[]}
{"11":[[2,"1"]]}
{"00":[[2,"0"]]}
{"1":[]}
```

## Julia

repstring returns a list of all of the substrings of its input that are the repeating units of a rep-string. If the input is not a valid rep-string, it returns an empty list. Julia indexes strings, including those that contain multi-byte characters, at the byte level. Because of this characteristic, repstring indexes its input using the chr2ind built-in.

```function repstring(r::AbstractString)
n = length(r)
replst = String[]
for m in 1:n÷2
s = r[1:chr2ind(r, m)]
if (s ^ cld(n, m))[1:chr2ind(r, n)] != r continue end
push!(replst, s)
end
return replst
end

tests = ["1001110011", "1110111011", "0010010010", "1010101010", "1111111111",
"0100101101", "0100100", "101", "11", "00", "1",
"\u2200\u2203\u2200\u2203\u2200\u2203\u2200\u2203"]

for r in tests
replst = repstring(r)
if isempty(replst)
println("\$r is not a rep-string.")
else
println("\$r is a rep-string of ", join(replst, ", "), ".")
end
end
```

{{out}}

```               1001110011 is a rep-string of 10011.
1110111011 is a rep-string of 1110.
0010010010 is a rep-string of 001.
1010101010 is a rep-string of 10, 1010.
1111111111 is a rep-string of 1, 11, 111, 1111, 11111.
0100101101 is not a rep-string.
0100100 is a rep-string of 010.
101 is not a rep-string.
11 is a rep-string of 1.
00 is a rep-string of 0.
1 is not a rep-string.
∀∃∀∃∀∃∀∃ is a rep-string of ∀∃, ∀∃∀∃.
```

## Kotlin

```// version 1.0.6

fun repString(s: String): MutableList<String> {
val reps = mutableListOf<String>()
if (s.length < 2) return reps
for (c in s) if (c != '0' && c != '1') throw IllegalArgumentException("Not a binary string")
for (len in 1..s.length / 2) {
val t = s.take(len)
val n = s.length / len
val r = s.length % len
val u = t.repeat(n) + t.take(r)
}
return reps
}

fun main(args: Array<String>) {
val strings = listOf(
"1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"
)
println("The (longest) rep-strings are:\n")
for (s in strings) {
val reps = repString(s)
val size = reps.size
println("\${s.padStart(10)} -> \${if (size > 0) reps[size - 1] else "Not a rep-string"}")
}
}
```

{{out}}

```
The (longest) rep-strings are:

1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 1010
1111111111 -> 11111
0100101101 -> Not a rep-string
0100100 -> 010
101 -> Not a rep-string
11 -> 1
00 -> 0
1 -> Not a rep-string

```

## LFE

The heavy lifting:

```
(defun get-reps (text)
(lists:filtermap
(lambda (x)
(case (get-rep text (lists:split x text))
('() 'false)
(x `#(true ,x))))
(lists:seq 1 (div (length text) 2))))

(defun get-rep
(case (string:str text tail)
(_ '()))))

```

Displaying the results:

```
(defun report
((`#(,text ()))
(io:format "~p has no repeating characters.~n" `(,text)))
((data)
(lists:map
#'report/1
(lists:zip data (lists:map #'get-reps/1 data)))
'ok))

```

Running the code:

```
> (set data '("1001110011"
"1110111011"
"0010010010"
"1010101010"
"1111111111"
"0100101101"
"0100100"
"101"
"11"
"00"
"1"))
> (report data)
"1001110011" repeats "10011" every 5 character(s).
"1110111011" repeats "1110" every 4 character(s).
"0010010010" repeats "001" every 3 character(s).
"1010101010" repeats "10" every 2 character(s).
"1111111111" repeats "1" every 1 character(s).
"0100101101" has no repeating characters.
"0100100" repeats "010" every 3 character(s).
"101" has no repeating characters.
"11" repeats "1" every 1 character(s).
"00" repeats "0" every 1 character(s).
"1" has no repeating characters.
ok

```

## Maple

The built-in `Period` command in the `StringTools` package computes the length of the longest repeated prefix.

```repstr? := proc( s :: string )
local   per := StringTools:-Period( s );
if 2 * per <= length( s ) then
true, s[ 1 .. per ]
else
false, ""
end if
end proc:
```

For the given set of test strings, we can generate the following output.

```
> Test := ["1001110011", "1110111011", "0010010010", "1010101010", "1111111111", \
"0100101101", "0100100", "101", "11", "00", "1"]:
> for s in Test do
>   printf( "%*s\t%5s   %s\n", 3 + max(map(length,Test)), s, repstr?( s ) )
> end do:
1001110011    true   10011
1110111011    true   1110
0010010010    true   001
1010101010    true   10
1111111111    true   1
0100101101   false
0100100    true   010
101   false
11    true   1
00    true   0
1   false

```

## Mathematica

Mathematica is based on pattern-based matching, so this is very easily implemented:

```RepStringQ[strin_String]:=StringCases[strin,StartOfString~~Repeated[x__,{2,\[Infinity]}]~~y___~~EndOfString/;StringMatchQ[x,StartOfString~~y~~___]:>x, Overlaps -> All]
```

Trying it out for the test-strings: str={"1001110011","1110111011","0010010010","1010101010","1111111111","0100101101","0100100","101","11","00","1"}; {#,RepStringQ[#]}&/@str//Grid

```
{{out}}

```txt
1001110011	{10011}
1110111011	{1110}
0010010010	{001}
1010101010	{1010,10,10}
1111111111	{11111,1111,111,11,11,1,1}
0100101101	{}
0100100		{010}
101		{}
11		{1}
00		{0}
1		{}
```

It outputs all the possibilities for a rep-string, if there is no rep-string it will show an empty list {}.

## NetRexx

{{trans|REXX}}

```/* NetRexx */
options replace format comments java crossref symbols nobinary

/* REXX ***************************************************************
* 11.05.2013 Walter Pachl
**********************************************************************/
runSample(arg)
return

/**
* Test for rep-strings
* @param s_str a string to check for rep-strings
* @return Rexx string: boolean indication of reps, length, repeated value
*/
method repstring(s_str) public static
s_str_n = s_str.length()
rep_str = ''
Loop lx = s_str.length() % 2 to 1 By -1
If s_str.substr(lx + 1, lx) = s_str.left(lx) Then Leave lx
End lx
If lx > 0 Then Do label reps
rep_str = s_str.left(lx)
Loop ix = 1 By 1
If s_str.substr(ix * lx + 1, lx) <> rep_str Then
Leave ix
End ix
If rep_str.copies(s_str_n).left(s_str.length()) <> s_str Then
rep_str = ''
End reps
Return (rep_str.length() > 0) rep_str.length() rep_str

-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
method runSample(arg) public static
parse arg samples
if samples = '' then -
samples = -
'1001110011' -
'1110111011' -
'0010010010' -
'1010101010' -
'1111111111' -
'0100101101' -
'0100100' -
'101' -
'11' -
'00' -
'1'

loop w_ = 1 to samples.words()
in_str = samples.word(w_)
parse repstring(in_str) is_rep_str rep_str_len rep_str

sq = ''''in_str''''
tstrlen = sq.length().max(20)
sq=sq.right(tstrlen)
if is_rep_str then
Say sq 'has a repetition length of' rep_str_len "i.e. '"rep_str"'"
else
Say sq 'is not a repeated string'
end w_
return

```

{{out}}

```
'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
'11' has a repetition length of 1 i.e. '1'
'00' has a repetition length of 1 i.e. '0'
'1' is not a repeated string

```

## NGS

{{trans|Python}}

```tests = [
'1001110011'
'1110111011'
'0010010010'
'1010101010'
'1111111111'
'0100101101'
'0100100'
'101'
'11'
'00'
'1'
]

F is_repeated(s:Str) (s.len()/2..0).first(F(x) s.starts_with(s[x..null]))

{
tests.each(F(test) {
local r = is_repeated(test)
echo("\${test} \${if r "has repetition of length \${r} (i.e. \${test[0..r]})" "is not a rep-string"}")
})
}
```

{{out}}

```1001110011 has repetition of length 5 (i.e. 10011)
1110111011 has repetition of length 4 (i.e. 1110)
0010010010 has repetition of length 3 (i.e. 001)
1010101010 has repetition of length 4 (i.e. 1010)
1111111111 has repetition of length 5 (i.e. 11111)
0100101101 is not a rep-string
0100100 has repetition of length 3 (i.e. 010)
101 is not a rep-string
11 has repetition of length 1 (i.e. 1)
00 has repetition of length 1 (i.e. 0)
1 is not a rep-string
```

## Nim

{{trans|Python}}

```import strutils

proc isRepeated(text): int =
for x in countdown(text.len div 2, 0):
if text.startsWith(text[x..text.high]): return x

const matchstr = """1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1"""

for line in matchstr.split():
let ln = isRepeated(line)
echo "'", line, "' has a repetition length of ", ln, " i.e ",
(if ln > 0: "'" & line[0 .. <ln] & "'" else: "*not* a rep-string")
```

{{Out}}

```'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 rep-string
'0100100' has a repetition length of 3 i.e '010'
'101' has a repetition length of 0 i.e *not* a rep-string
'11' has a repetition length of 1 i.e '1'
'00' has a repetition length of 1 i.e '0'
'1' has a repetition length of 0 i.e *not* a rep-string
```

## Objeck

```class RepString {
function : Main(args : String[]) ~ Nil {
strings := ["1001110011", "1110111011", "0010010010", "1111111111",
"0100101101", "0100100", "101", "11", "00", "1"];
each(i : strings) {
string := strings[i];
repstring := RepString(string);
if(repstring->Size() > 0) {
"\"{\$string}\" = rep-string \"{\$repstring}\""->PrintLine();
}
else {
"\"{\$string}\" = not a rep-string"->PrintLine();
};
};
}

function : RepString(string : String) ~ String {
offset := string->Size() / 2;

while(offset > 0) {
left := string->SubString(offset);
right := string->SubString(left->Size(),left->Size());
if(left->Equals(right)) {
if(ValidateMatch(left, string)) {
return left;
}
else {
return "";
};
};

offset--;
};

return "";
}

function : ValidateMatch(left : String, string : String) ~ Bool {
parts := string->Size() / left->Size();
tail := string->Size() % left->Size() <> 0;

for(i := 1; i < parts; i+=1;) {
offset := i * left->Size();
right := string->SubString(offset, left->Size());
if(<>left->Equals(right)) {
return false;
};
};

if(tail) {
offset := parts * left->Size();
right := string->SubString(offset, string->Size() - offset);
each(i : right) {
if(left->Get(i) <> right->Get(i)) {
return false;
};
};
};

return true;
}
}
```

Output:

```
"1001110011" = rep-string "10011"
"1110111011" = rep-string "1110"
"0010010010" = rep-string "001"
"1111111111" = rep-string "11111"
"0100101101" = not a rep-string
"0100100" = rep-string "010"
"101" = not a rep-string
"11" = rep-string "1"
"00" = rep-string "0"
"1" = not a rep-string

```

## Oforth

Returns null if no rep string.

```: repString(s)
| sz i |
s size dup ->sz 2 / 1 -1 step: i [
s left(sz i - ) s right(sz i -) == ifTrue: [ s left(i) return ]
]
null ;
```

{{Out}}

```
["1001110011", "1110111011", "0010010010", "1010101010", "1111111111", "0100101101", "0100100", "101", "11", "00", "1"]
map(#repString) .
[10011, 1110, 001, 1010, 11111, null, 010, null, 1, 0, null] ok

```

## PARI/GP

```rep(v)=for(i=1,#v\2,for(j=i+1,#v,if(v[j]!=v[j-i],next(2)));return(i));0;
v=["1001110011","1110111011","0010010010","1010101010","1111111111","0100101101","0100100","101","11","00","1"];
for(i=1,#v,print(v[i]" "rep(Vec(v[i]))))
```

{{out}}

```1001110011 5
1110111011 4
0010010010 3
1010101010 2
1111111111 1
0100101101 0
0100100 3
101 0
11 1
00 1
1 0
```

## Perl

```foreach (qw(1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 00 1)) {
print "\$_\n";
if (/^(.+)\1+(.*\$)(?(?{ substr(\$1, 0, length \$2) eq \$2 })|(?!))/) {
print ' ' x length \$1, "\$1\n\n";
} else {
print " (no repeat)\n\n";
}
}
```

{{out}}

```1001110011
10011

1110111011
1110

0010010010
001

1010101010
1010

1111111111
11111

0100101101
(no repeat)

0100100
010

101
(no repeat)

11
1

00
0

1
(no repeat)
```

## Perl 6

``` {
if /^ (.+) \$0+: (.*\$) <?{ \$0.substr(0,\$1.chars) eq \$1 }> / {
my \$rep = \$0.chars;
say .substr(0,\$rep), .substr(\$rep,\$rep).trans('01' => '𝟘𝟙'), .substr(\$rep*2);
}
else {
say "\$_ (no repeat)";
}
}
```

{{out}}

```10011𝟙𝟘𝟘𝟙𝟙
1110𝟙𝟙𝟙𝟘11
001𝟘𝟘𝟙0010
1010𝟙𝟘𝟙𝟘10
11111𝟙𝟙𝟙𝟙𝟙
0100101101 (no repeat)
010𝟘𝟙𝟘0
101 (no repeat)
1𝟙
0𝟘
1 (no repeat)
```

Here's a technique that relies on the fact that XORing the shifted binary number should set all the lower bits to 0 if there are repeats. (The cool thing is that shift will automatically throw away the bits on the right that you want thrown away.) This produces the same output as above.

```sub repstr(Str \$s) {
my \$bits = :2(\$s);
for reverse 1 .. \$s.chars div 2 -> \$left {
my \$right = \$s.chars - \$left;
return \$left if \$bits +^ (\$bits +> \$left) == \$bits +> \$right +< \$right;
}
}

for '1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 00 1'.words {
if repstr \$_ -> \$rep {
say .substr(0,\$rep), .substr(\$rep,\$rep).trans('01' => '𝟘𝟙'), .substr(\$rep*2);
}
else {
say "\$_ (no repeat)";
}
}
```

## Phix

{{trans|Julia}} Shows all possible repeated sub-strings, as Julia, but in the output style of Perl/Elixir

```function list_reps(string r)
sequence replist = {}
integer n = length(r)
for m=1 to floor(n/2) do
string s = r[1..m]
if join(repeat(s,floor(n/m)+1),"")[1..n]=r then
replist = append(replist,s)
end if
end for
return replist
end function

constant tests = {"1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"}

for i=1 to length(tests) do
printf(1,"%s\n",{tests[i]})
sequence replist = list_reps(tests[i])
if length(replist)=0 then
printf(1,"not a rep-string.\n")
else
for j=1 to length(replist) do
string rj = replist[j],
end for
end if
printf(1,"\n")
end for
```

{{out}}

```
1001110011
10011

1110111011
1110

0010010010
001

1010101010
10
1010

1111111111
1
11
111
1111
11111

0100101101
not a rep-string.

0100100
010

101
not a rep-string.

11
1

00
0

1
not a rep-string.

```

## PicoLisp

```(de repString (Str)
(let Lst (chop Str)
(for (N (/ (length Lst) 2)  (gt0 N)  (dec N))
(T
(use (Lst X)
(let H (cut N 'Lst)
(loop
(setq X (cut N 'Lst))
(NIL Lst T) ) ) )
N ) ) ) )
```

Test:

```(test 5 (repString "1001110011"))
(test 4 (repString "1110111011"))
(test 3 (repString "0010010010"))
(test 4 (repString "1010101010"))
(test 5 (repString "1111111111"))
(test NIL (repString "0100101101"))
(test 3 (repString "0100100"))
(test NIL (repString "101"))
(test 1 (repString "11"))
(test 1 (repString "00"))
(test NIL (repString "1"))
(test NIL (repString "0100101"))
```

## PL/I

{{Incorrect|PL/I|"0100101101" is not a rep-string.}}

```rep: procedure options (main); /* 5 May 2015 */
declare s bit (10) varying;
declare (i, k) fixed binary;

main_loop:
do s = '1001110011'b, '1110111011'b, '0010010010'b, '1010101010'b,
'1111111111'b, '0100101101'b, '0100100'b, '101'b, '11'b, '00'b, '1'b;
k = length(s);
do i = k/2 to 1 by -1;
if substr(s, 1, i) = substr(s, i+1, i) then
do;
put skip edit (s, ' is a rep-string containing ', substr(s, 1, i) ) (a);
iterate main_loop;
end;
end;
put skip edit (s, ' is not a rep-string') (a);
end;

end rep;
```

{{Out}}

```
1001110011 is a rep-string containing 10011
1110111011 is a rep-string containing 1110
0010010010 is a rep-string containing 001
1010101010 is a rep-string containing 1010
1111111111 is a rep-string containing 11111
0100101101 is a rep-string containing 010
0100100 is a rep-string containing 010
101 is not a rep-string
11 is a rep-string containing 1
00 is a rep-string containing 0
1 is not a rep-string

```

## Prolog

Using SWI-Prolog 7 library(func), for some functional syntax.

```:- use_module(library(func)).

%% Implementation logic:

test_for_repstring(String, (String, Result, Reps)) :-
( setof(Rep, repstring(String, Rep), Reps)
-> Result = 'no repstring'
;  Result = 'repstrings', Reps = []
).

repstring(Codes, R) :-
RepLength = between(1) of (_//2) of length \$ Codes,
length(R, RepLength),
phrase( (rep(R), prefix(~,R)),
Codes).

rep(X) --> X, X.
rep(X) --> X, rep(X).

%% Demonstration output:

test_strings([`1001110011`, `1110111011`, `0010010010`, `1010101010`,
`1111111111`, `0100101101`, `0100100`, `101`, `11`, `00`, `1`]).

report_repstring((S,Result,Reps)):-
format('~s -- ~w: ', [S, Result]),
foreach(member(R, Reps), format('~s, ', [R])), nl.

report_repstrings :-
Results = maplist(test_for_repstring) \$ test_strings(~),
maplist(report_repstring, Results).
```

Output

```?-  report_repstrings.
1001110011 -- repstrings: 10011,
1110111011 -- repstrings: 1110,
0010010010 -- repstrings: 001,
1010101010 -- repstrings: 10, 1010,
1111111111 -- repstrings: 1, 11, 111, 1111, 11111,
0100101101 -- no repstring:
0100100 -- repstrings: 010,
101 -- no repstring:
11 -- repstrings: 1,
00 -- repstrings: 0,
1 -- no repstring:
true.
```

## PureBasic

```a\$="1001110011"+#CRLF\$+"1110111011"+#CRLF\$+"0010010010"+#CRLF\$+"1010101010"+#CRLF\$+"1111111111"+#CRLF\$+
"0100101101"+#CRLF\$+"0100100"   +#CRLF\$+"101"       +#CRLF\$+"11"        +#CRLF\$+"00"        +#CRLF\$+
"1"         +#CRLF\$

OpenConsole()

Procedure isRepStr(s1\$,s2\$)
If Int(Len(s1\$)/Len(s2\$))>=2 : ProcedureReturn isRepStr(s1\$,s2\$+s2\$)                         : EndIf
If Len(s1\$)>Len(s2\$)         : ProcedureReturn isRepStr(s1\$,s2\$+Left(s2\$,Len(s1\$)%Len(s2\$))) : EndIf
If s1\$=s2\$                   : ProcedureReturn #True : Else : ProcedureReturn #False         : EndIf
EndProcedure

For k=1 To CountString(a\$,#CRLF\$)
s1\$=StringField(a\$,k,#CRLF\$) : s2\$=Left(s1\$,Len(s1\$)/2)
While Len(s2\$)
r=isRepStr(s1\$,s2\$)
If Not r : s2\$=Left(s2\$,Len(s2\$)-1) : Else : Break : EndIf
Wend
If Len(s2\$) And r : PrintN(LSet(s1\$,15,Chr(32))+#TAB\$+"longest sequence: "+s2\$) : EndIf
If Not Len(s2\$)   : PrintN(LSet(s1\$,15,Chr(32))+#TAB\$+"found nothing.")         : EndIf
Next
Input()
```

{{out}}

```1001110011      longest sequence: 10011
1110111011      longest sequence: 1110
0010010010      longest sequence: 001
1010101010      longest sequence: 1010
1111111111      longest sequence: 11111
0100101101      found nothing.
0100100         longest sequence: 010
101             found nothing.
11              longest sequence: 1
00              longest sequence: 0
1               found nothing.
```

## Python

### Python: Procedural

```def is_repeated(text):
'check if the first part of the string is repeated throughout the string'
for x in range(len(text)//2, 0, -1):
if text.startswith(text[x:]): return x
return 0

matchstr = """\
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
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 rep-string'))
```

{{out}}

```'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 rep-string
'0100100' has a repetition length of 3 i.e. '010'
'101' has a repetition length of 0 i.e. *not* a rep-string
'11' has a repetition length of 1 i.e. '1'
'00' has a repetition length of 1 i.e. '0'
'1' has a repetition length of 0 i.e. *not* a rep-string
```

### Python: Functional

This returns all the possible repeated substrings

``` def reps(text):
return [text[:x] for x in range(1, 1 + len(text) // 2)
if text.startswith(text[x:])]

>>> matchstr = """\
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1
"""
>>> print('\n'.join('%r has reps %r' % (line, reps(line)) for line in matchstr.split()))
'1001110011' has reps ['10011']
'1110111011' has reps ['1110']
'0010010010' has reps ['001']
'1010101010' has reps ['10', '1010']
'1111111111' has reps ['1', '11', '111', '1111', '11111']
'0100101101' has reps []
'0100100' has reps ['010']
'101' has reps []
'11' has reps ['1']
'00' has reps ['0']
'1' has reps []
>>>
```

And we could also express this in terms of '''itertools.cycle''' {{Trans|Haskell}} {{Works with|Python|3.7}}

```'''Rep-strings'''

from itertools import (accumulate, chain, cycle, islice)

# repCycles :: String -> [String]
def repCycles(s):
'''Repeated sequences of characters in s.'''
n = len(s)
cs = list(s)

return [
x for x in
tail(inits(take(n // 2)(s)))
if cs == take(n)(cycle(x))
]

# TEST ----------------------------------------------------
# main :: IO ()
def main():
'''Tests - longest cycle (if any) in each string.'''
print(
fTable('Longest cycles:\n')(repr)(
lambda xs: ''.join(xs[-1]) if xs else '(none)'
)(repCycles)([
'1001110011',
'1110111011',
'0010010010',
'1010101010',
'1111111111',
'0100101101',
'0100100',
'101',
'11',
'00',
'1',
])
)

# GENERIC -------------------------------------------------

# inits :: [a] -> [[a]]
def inits(xs):
'''all initial segments of xs, shortest first.'''
return accumulate(chain([[]], xs), lambda a, x: a + [x])

# tail :: [a] -> [a]
# tail :: Gen [a] -> [a]
def tail(xs):
'''The elements following the head of a
(non-empty) list or generator stream.'''
if isinstance(xs, list):
return xs[1:]
else:
list(islice(xs, 1))  # First item dropped.
return xs

# take :: Int -> [a] -> [a]
# take :: Int -> String -> String
def take(n):
'''The prefix of xs of length n,
or xs itself if n > length xs.'''
return lambda xs: (
xs[0:n]
if isinstance(xs, (list, tuple))
else list(islice(xs, n))
)

# OUTPUT FORMATTING ---------------------------------------

# fTable :: String -> (a -> String) ->
#                     (b -> String) -> (a -> b) -> [a] -> String
def fTable(s):
'''Heading -> x display function ->
fx display function ->
f -> value list -> tabular string.
'''
def go(xShow, fxShow, f, xs):
ys = [xShow(x) for x in xs]
w = max(map(len, ys))
return s + '\n' + '\n'.join(map(
lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)),
xs, ys
))
return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
xShow, fxShow, f, xs
)

# MAIN ---
if __name__ == '__main__':
main()
```

{{Out}}

```Longest cycles:

'1001110011' -> 10011
'1110111011' -> 1110
'0010010010' -> 001
'1010101010' -> 1010
'1111111111' -> 11111
'0100101101' -> (none)
'0100100' -> 010
'101' -> (none)
'11' -> 1
'00' -> 0
'1' -> (none)
```

### 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.

```import re

matchstr = """\
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
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 rep-string' % (g0,)

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

checkit(matchstr)
```

{{out}}

```'1001110011' repeats '10011'
'1110111011' repeats '1110'
'0010010010' repeats '001'
'1010101010' repeats '1010'
'1111111111' repeats '11111'
'0100101101' is not a rep-string
'0100100' repeats '010'
'101' is not a rep-string
'11' repeats '1'
'00' repeats '0'
'1' is not a rep-string
```

### Python: find

See [https://stackoverflow.com/questions/29481088/how-can-i-tell-if-a-string-repeats-itself-in-python/29489919#29489919 David Zhang's solution] to the same question posed on Stack Overflow.

## Racket

```#lang racket

(define (rep-string str)
(define len (string-length str))
(for/or ([n (in-range 1 len)])
(and (let loop ([from n])
(or (>= from len)
(let ([m (min (- len from) n)])
(and (equal? (substring str from (+ from m))
(substring str 0 m))
(loop (+ n from))))))
(<= n (quotient len 2))
(substring str 0 n))))

(for ([str '("1001110011"
"1110111011"
"0010010010"
"1010101010"
"1111111111"
"0100101101"
"0100100"
"101"
"11"
"00"
"1")])
(printf "~a => ~a\n" str (or (rep-string str) "not a rep-string")))
```

{{Out}}

```1001110011 => 10011
1110111011 => 1110
0010010010 => 001
1010101010 => 10
1111111111 => 1
0100101101 => not a rep-string
0100100 => 010
101 => not a rep-string
11 => 1
00 => 0
1 => not a rep-string
```

## REXX

### version 1

```/* REXX ***************************************************************
* 11.05.2013 Walter Pachl
* 14.05.2013 Walter Pachl extend to show additional rep-strings
**********************************************************************/
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 '11'
Call repstring '00'
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 Do
Call show_rep rep_str              /* show result                */
Do i=length(rep_str)-1 To 1 By -1  /* look for shorter rep_str-s */
rep_str=left(s,i)
If left(copies(rep_str,n),length(s))=s Then
Call show_rep rep_str
End
End
Else
Call show_norep
End
Else
Call show_norep
Return

show_rep:
Parse Arg rs
Say right(sq,12) 'has a repetition length of' length(rs) 'i.e.' ''''rs''''
Return
show_norep:
Say right(sq,12) 'is not a repeated string'
Return
```

{{Out}}

```'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'
'1010101010' has a repetition length of 2 i.e. '10'
'1111111111' has a repetition length of 5 i.e. '11111'
'1111111111' has a repetition length of 4 i.e. '1111'
'1111111111' has a repetition length of 3 i.e. '111'
'1111111111' has a repetition length of 2 i.e. '11'
'1111111111' has a repetition length of 1 i.e. '1'
'0100101101' is not a repeated string
'0100100' has a repetition length of 3 i.e. '010'
'101' is not a repeated string
'11' has a repetition length of 1 i.e. '1'
'00' has a repetition length of 1 i.e. '0'
'1' is not a repeated string
```

### version 2

A check was added to validate if the strings are binary strings. The binary strings can be of any length.

```/*REXX pgm determines  if  a string is a repString, it returns minimum length repString.*/
parse arg s                                      /*get optional strings from the C.L.   */
if s=''  then s=1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 00 1 45
/* [↑]  S  not specified?  Use defaults*/
do k=1  for words(s);   _=word(s,k);   w=length(_)       /*process binary strings. */
say right(_,max(25,w))  repString(_)                     /*show repString & result.*/
end   /*k*/                                 /* [↑]  the  "result"  may be negatory.*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
repString: procedure;  parse arg x;              L=length(x);         @rep='  rep string='
if \datatype(x,'B')  then return "  ***error***  string isn't a binary string."
h=L%2
do j=1  for L-1  while  j<=h;        \$=left(x,j);     \$\$=copies(\$,L)
if left(\$\$,L)==x  then  return @rep    left(\$,15)     "[length"     j']'
end   /*j*/                    /* [↑]  we have found a good repString.*/
return               '      (no repetitions)'    /*failure to find repString.*/
```

'''output''' when using the default binary strings for input:

```
1001110011   rep string= 10011           [length 5]
1110111011   rep string= 1110            [length 4]
0010010010   rep string= 001             [length 3]
1010101010   rep string= 10              [length 2]
1111111111   rep string= 1               [length 1]
0100101101       (no repetitions)
0100100   rep string= 010             [length 3]
101       (no repetitions)
11   rep string= 1               [length 1]
00   rep string= 0               [length 1]
1       (no repetitions)
45   ***error***  string isn't a binary string.

```

## Ring

```
# Project : Rep-string

test = ["1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"]

for n = 1 to len(test)
strend = ""
for m=1 to len(test[n])
strbegin = substr(test[n], 1, m)
strcut = right(test[n], len(test[n]) - m)
nr = substr(strcut, strbegin)
if nr=1 and len(test[n]) > 1
strend = strbegin
ok
next
if strend = ""
see "" + test[n] + " -> (none)" + nl
else
see "" + test[n] + " -> " + strend + nl
ok
next

```

Output:

```
1001110011 -> 10011
1110111011 -> 1110
0010010010 -> 001
1010101010 -> 1010
1111111111 -> 11111
0100101101 -> 010
0100100 -> 010
101 -> (none)
11 -> 1
00 -> 0
1 -> (none)

```

## Ruby

```ar = %w(1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1)

ar.each do |str|
rep_pos = (str.size/2).downto(1).find{|pos| str.start_with? str[pos..-1]}
puts str, rep_pos ? " "*rep_pos + str[0, rep_pos] : "(no repetition)", ""
end
```

{{Out|Output (as Perl)}}

```1001110011
10011

1110111011
1110

0010010010
001

1010101010
1010

1111111111
11111

0100101101
(no repetition)

0100100
010

101
(no repetition)

11
1

00
0

1
(no repetition)
```

## Scala

```object RepString extends App {
def repsOf(s: String) = s.trim match {
case s if s.length < 2 => Nil
case s => (1 to (s.length/2)).map(s take _)
.filter(_ * s.length take s.length equals s)
}

val tests = Array(
"1001110011",
"1110111011",
"0010010010",
"1010101010",
"1111111111",
"0100101101",
"0100100",
"101",
"11",
"00",
"1"
)
def printReps(s: String) = repsOf(s) match {
case Nil => s+": NO"
case r => s+": YES ("+r.mkString(", ")+")"
}
val todo = if (args.length > 0) args else tests
todo.map(printReps).foreach(println)
}
```

{{out}}

```1001110011: YES (10011)
1110111011: YES (1110)
0010010010: YES (001)
1010101010: YES (10, 1010)
1111111111: YES (1, 11, 111, 1111, 11111)
0100101101: NO
0100100: YES (010)
101: NO
11: YES (1)
00: YES (0)
1: NO
```

## Seed7

```\$ include "seed7_05.s7i";

const func integer: repeatLength (in string: text) is func
result
var integer: length is 0;
local
var integer: pos is 0;
begin
for pos range succ(length(text) div 2) downto 1 until length <> 0 do
if startsWith(text, text[pos ..]) then
length := pred(pos);
end if;
end for;
end func;

const proc: main is func
local
var string: line is "";
var integer: length is 0;
begin
for line range [] ("1001110011", "1110111011", "0010010010", "1010101010",
"1111111111", "0100101101", "0100100", "101", "11", "00", "1") do
length := repeatLength(line);
if length = 0 then
writeln("No rep-string for " <& literal(line));
else
writeln("Longest rep-string for " <& literal(line) <& ": " <& literal(line[.. length]));
end if;
end for;
end func;
```

{{out}}

```
Longest rep-string for "1001110011": "10011"
Longest rep-string for "1110111011": "1110"
Longest rep-string for "0010010010": "001"
Longest rep-string for "1010101010": "1010"
Longest rep-string for "1111111111": "11111"
No rep-string for "0100101101"
Longest rep-string for "0100100": "010"
No rep-string for "101"
Longest rep-string for "11": "1"
Longest rep-string for "00": "0"
No rep-string for "1"

```

## Sidef

```var arr = <1001110011 1110111011
0010010010 1010101010
1111111111 0100101101
0100100  101  11 00 1>;

arr.each { |n|
if (var m = /^(.+)\1+(.*\$)(?(?{ substr(\$1, 0, length \$2) eq \$2 })|(?!))/.match(n)) {
var i = m[0].len;
say (n.substr(0, i),
n.substr(i, i).tr('01', '𝟘𝟙'),
n.substr(i*2));
} else {
say "#{n} (no repeat)";
}
}
```

{{out}}

```10011𝟙𝟘𝟘𝟙𝟙
1110𝟙𝟙𝟙𝟘11
001𝟘𝟘𝟙0010
1010𝟙𝟘𝟙𝟘10
11111𝟙𝟙𝟙𝟙𝟙
0100101101 (no repeat)
010𝟘𝟙𝟘0
101 (no repeat)
1𝟙
0𝟘
1 (no repeat)
```

## Swift

```import Foundation

func repString(_ input: String) -> [String] {
return (1..<(1 + input.count / 2)).compactMap({x -> String? in
let i = input.index(input.startIndex, offsetBy: x)
return input.hasPrefix(input[i...]) ? String(input.prefix(x)) : nil
})
}

let testCases = """
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1
""".components(separatedBy: "\n")

for testCase in testCases {
print("\(testCase) has reps: \(repString(testCase))")
}
```

{{out}}

```1001110011 has reps: ["10011"]
1110111011 has reps: ["1110"]
0010010010 has reps: ["001"]
1010101010 has reps: ["10", "1010"]
1111111111 has reps: ["1", "11", "111", "1111", "11111"]
0100101101 has reps: []
0100100 has reps: ["010"]
101 has reps: []
11 has reps: ["1"]
00 has reps: ["0"]
1 has reps: []
```

## Tcl

```proc repstring {text} {
set len [string length \$text]
for {set i [expr {\$len/2}]} {\$i > 0} {incr i -1} {
set sub [string range \$text 0 [expr {\$i-1}]]
set eq [string repeat \$sub [expr {int(ceil(\$len/double(\$i)))}]]
if {[string equal -length \$len \$text \$eq]} {
return \$sub
}
}
error "no repetition"
}
```

Demonstrating:

```foreach sample {
"1001110011" "1110111011" "0010010010" "1010101010" "1111111111"
"0100101101" "0100100" "101" "11" "00" "1"
} {
if {[catch {
set rep [repstring \$sample]
puts [format "\"%s\" has repetition (length: %d) of \"%s\"" \
\$sample [string length \$rep] \$rep]
}]} {
puts [format "\"%s\" is not a repeated string" \$sample]
}
}
```

{{out}}

```
"1001110011" has repetition (length: 5) of "10011"
"1110111011" has repetition (length: 4) of "1110"
"0010010010" has repetition (length: 3) of "001"
"1010101010" has repetition (length: 4) of "1010"
"1111111111" has repetition (length: 5) of "11111"
"0100101101" is not a repeated string
"0100100" has repetition (length: 3) of "010"
"101" is not a repeated string
"11" has repetition (length: 1) of "1"
"00" has repetition (length: 1) of "0"
"1" is not a repeated string

```

## UNIX Shell

{{trans|Tcl}} {{works with|bash}}

```is_repeated() {
local str=\$1 len rep part
for (( len = \${#str} / 2; len > 0; len-- )); do
part=\${str:0:len}
rep=""
while (( \${#rep} < \${#str} )); do
rep+=\$part
done
if [[ \${rep:0:\${#str}} == \$str ]] && (( \$len < \${#str} )); then
echo "\$part"
return 0
fi
done
return 1
}

if part=\$( is_repeated "\$test" ); then
echo "\$test is composed of \$part repeated"
else
echo "\$test is not a repeated string"
fi
done <<END_TESTS
1001110011
1110111011
0010010010
1010101010
1111111111
0100101101
0100100
101
11
00
1
END_TESTS
```

{{out}}

```1001110011 is composed of 10011 repeated
1110111011 is composed of 1110 repeated
0010010010 is composed of 001 repeated
1010101010 is composed of 1010 repeated
1111111111 is composed of 11111 repeated
0100101101 is not a repeated string
0100100 is composed of 010 repeated
101 is not a repeated string
11 is composed of 1 repeated
00 is composed of 0 repeated
1 is not a repeated string
```

## VBScript

```
Function rep_string(s)
max_len = Int(Len(s)/2)
tmp = ""
If max_len = 0 Then
rep_string = "No Repeating String"
Exit Function
End If
For i = 1 To max_len
If InStr(i+1,s,tmp & Mid(s,i,1))Then
tmp = tmp & Mid(s,i,1)
Else
Exit For
End If
Next
Do While Len(tmp) > 0
If Mid(s,Len(tmp)+1,Len(tmp)) = tmp Then
rep_string = tmp
Exit Do
Else
tmp = Mid(tmp,1,Len(tmp)-1)
End If
Loop
If Len(tmp) > 0 Then
rep_string = tmp
Else
rep_string = "No Repeating String"
End If
End Function

'testing the function
arr = Array("1001110011","1110111011","0010010010","1010101010",_
"1111111111","0100101101","0100100","101","11","00","1")

For n = 0 To UBound(arr)
WScript.StdOut.Write arr(n) & ": " & rep_string(arr(n))
WScript.StdOut.WriteLine
Next

```

{{Out}}

```
1001110011: 10011
1110111011: 1110
0010010010: 001
1010101010: 1010
1111111111: 11111
0100101101: 010
0100100: 010
101: No Repeating String
11: 1
00: 0
1: No Repeating String

```

## Yabasic

```data "1001110011", "1110111011", "0010010010", "1010101010", "1111111111", "0100101101", "0100100", "101", "11", "00", "1", ""

sub rep\$(c\$, n)
local r\$, i

for i = 1 to n
r\$ = r\$ + c\$
next
return r\$
end sub

do
read p\$ : if p\$ = "" break
b\$ = "" : l = len(p\$) : m = int(l / 2)

for i = m to 1 step -1
t\$ = left\$(p\$, i)
s\$ = rep\$(t\$, l / i + 1)
if p\$ = left\$(s\$, l) b\$ = t\$ : break
next

if b\$ = "" then
print p\$, " is not a repeated string"
else
print p\$, " is composed of ", b\$, " repeated"
end if
loop
```

## zkl

{{trans|D}}

```fcn repString(s){
foreach n in ([s.len()/2+1..1,-1]){
Walker.cycle(s[0,n]).pump(s.len(),String) :
if(_==s and n*2<=s.len()) return(n);
}
return(False)
}
```

{{trans|Python}}

```fcn repString(s){
foreach n in ([s.len()/2..0,-1]){
if(s.matches(s[n,*] + "*") and n*2<=s.len()) return(n);
}
return(False)
}
```
```words:=("1001110011 1110111011 0010010010 1010101010 "
"1111111111 0100101101 0100100 101 11 00 1").split(" ");
foreach w in (words){
if(not n:=repString2(w)) "No repeat in ".println(w);
else [0..*,n].tweak('wrap(z){ if(s:=w[z,n]) s else Void.Stop })
.walk().concat(" ").println();
}
```

{{out}}

```
10011 10011
1110 1110 11
001 001 001 0
1010 1010 10
11111 11111
No repeat in 0100101101
010 010 0
No repeat in 101
1 1
0 0
No repeat in 1

```