With use warnings it gives a Use of uninitialized value in string eq at... warning. Small off-by-one error.

Replacing

   push @tmp, $a[$_]
      if ( $a[$_ + 1]) eq ( $b[$map{$a[$_]} + 1] )
         or @tmp >= 1;
[download]

with

    push @tmp, $a[$_]
      if ($a[$_ + 1] and $b[$map{$a[$_]} + 1]
          and ( $a[$_ + 1]) eq ( $b[$map{$a[$_]} + 1] )
          or @tmp >= 1);
[download]

makes Perl happy again.

Arjen