Find duplicates within a list in O(n) keeping original order

#!/usr/bin/perl -w

# Find duplicates.
# Input is a list of numbers separated by space, from STDIN, example: 5 23 7 3 5 89 12 -34 7 355 0 0 12 5
# Output is a list of numbers separated by space, on STDOUT, example: 5 7 12 0

use strict;
use warnings;

my $input = <STDIN>;
chomp($input);

my $list = [ split /\ /, $input ];
my $dups = dups($list);
print join(" ", @{$dups})."\n";

sub dups {
    my $list = shift;

    my $visited = {};
    my $dups = {};
    my $result = [];

    foreach my $item (@{$list}) {
        if(defined $visited->{$item}) { # dup
            if(!defined $dups->{$item}) { # avoid storing dups twice
                $dups->{$item} = 1;
                push @{$result}, $item;
            }
        }
        $visited->{$item} = 1;
    }

    return $result;
}