#!/usr/bin/perl

use warnings;
use strict;

my @a1 = sort qw(foo bar blarn schmark floogle foo blarn);
my @a2 = sort qw(flirp schnirp blarn floogle florn flimple flange);
my @a3 = sort qw(bar bar floogle bar florn bar bar);

my $sml = SortedMultiList->new(\@a1,\@a2,\@a3);

my $last;
while (defined(my $next = $sml->shift_lowest))
{
  print $next,"\n"
      if (!defined($last) or ($last ne $next));
  $last = $next;
}

package SortedMultiList;

sub new
{
  my $class = shift;
  my $self = [@_];
  bless $self, $class;
}

sub shift_lowest
{
  my $self = shift;
  my($lowest_arr,$lowest);
  foreach my $a (@$self)
  {
    next unless (@$a);
    if (!defined($lowest) or ($a->[0] lt $lowest))
    {
      $lowest_arr = $a;
      $lowest = $a->[0];
    }
  }
  return $lowest_arr
           ? shift(@$lowest_arr)
	   : undef;
}