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my @tst = qw( A,G AG,CT TC,CA GAT,CGA CGAT,TG ,G ACGT X,A AA,G AC,GGC ATGA,TGG ATCXG,AAC ... my $side = qr/(?:([ACGT])(?![^,]*\g{-1}))+/; print $_ . (/^$side,$side$/ ? ' good' : ' bad') . $/; }
A,G good AG,CT good ... AC,GGC bad ATGA,TGG bad ATCXG,AAC bad