Rep-string

for <1001110011 1110111011 0010010010 1010101010 1111111111 0100101101 0100100 101 11 00 1> {
    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)";
    }
}

Output:

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)";
    }
}