This may not be the best solution, but as ever, TMTOWTDI¹ ;-)

#!/usr/bin/perl -w

use strict;
use vars qw( @array %hash $number );

@array = (1,1,1,1,1,1,2,2,2,2,2,2,2,3,3,3,3,3,3);

print "@array\n";

foreach $number (@array){
    $hash{$number}++;
}

@array = keys %hash;

print "@array\n";
[download]

---

1:There's More Than One Way To Do It