use warnings;
use strict;

my @array = (23,1,2,3,4,2,3,5,8);
my $cc;
my @uniq = map { $_->[0] }
          sort { $a->[1] <=> $b->[1]}
          grep {! $_->[2]}
          sort { my $v = $a->[0] cmp $b->[0];
               
  $a->[2] = 1 unless $v or $b->[2];
               
  $v}
           map {[$_,$cc++]} @array;

print "$_," for @uniq;