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use v5.20;
use Data::Dump "pp";

...
{
    $j =~ $z and say pp {$j => \@- };
}

...
{ acbcaa => [0, 6, 6, 3, 3, 4, 4] }
{ acbcab => [0, 5, 5, 6, 6, 4, 4] }
...
{ cccbca => [0, 6, 6, 4, 4, 5, 5] }
{ ccccab => [0, 5, 5, 6, 6, 4, 4] }
{ ccccba => [0, 6, 6, 5, 5, 4, 4] }

my @y = glob('{a,b,c}'x6);
my $y = '(?:(?!\1)a()|(?!\2)a()|(?!\3)b()|(?!\4)b()|(?!\5)c()|(?!\6)c(
+)){6}\1\2\3\4\5\6';

...
{
    $j =~ $y and say $j;
}

aabbcc
aabcbc
aabccb
...
ccbaab
ccbaba
ccbbaa

# edit reformatted as a multiline regex for clarity
my $y = qr/(?:
               (?!\1) a ()
...
             | (?!\6) c ()
           ){6}
         /x;