#!/your/perl/here
use strict;
use warnings;

my $str="17:43:33:21:23:19:27:6";      
my %hash=split/:/,$str;                
my $count;
my %ad_lookup;
foreach my $k(keys %hash)              
{              
    $count += $k;                        
    $ad_lookup{$count} = $hash{$k};
}                        

my @ad_lookup_sorted_keys = sort {$b <=> $a} keys %ad_lookup;

my %seen;
for my $rand ( 1..$count )
{
#	my $rand = rand($count);    
	my $adid;
	foreach my $key ( @ad_lookup_sorted_keys )
	{
	    if ( $rand <= $key )
	    {
	        $adid = $ad_lookup{$key};
	    }
	    else
	    {
	        last;
	    }
	}
#	print "$adid\n";
	$seen{$adid}++;
}
foreach my $k ( sort {$a <=> $b} keys %seen )
{
	print "\$seen{$k}: $seen{$k}\n";
}

##</code><code>##

$seen{6}: 27
$seen{19}: 23
$seen{21}: 33
$seen{43}: 17

##</code><code>##

    $ad_lookup{$count} = $hash{$k};

##</code><code>##

    $ad_lookup{$count-1} = $hash{$k};