#!/usr/bin/perl -w
use strict;

my @array1 = ( 1 .. 10 );
my @array2 = ( qw(a b c) , [ 28, 42, 84 ] , 'foo bar' );

push @array1 , \@array2;
push @array2 , \@array1;

print join ' , ' , flatten(\@array1 , \@array2);

sub flatten {
   my @stack = @_;
   my @flat;
   my %seen;

   $seen{$_} = 1 for @stack;

   while ( @stack ) {
       my $array = shift @stack;
       for my $element ( @$array ) {
           if ( ref $element eq 'ARRAY') {
               if ( ! $seen{$element} ) {
                   $seen{$element} = 1;
                   unshift @stack , $element;
               }
           }
           else {
               push @flat , $element;
           }
       }
   }

   return wantarray ? @flat : \@flat;
}