use strict;
use warnings;

my $string = "1:1,2:1,3:2,500:2,505:1";
my (@array, %hash);


$string =~ s/(\d+):(\d+)(?:,|$)/$hash{$1}=$2;push(@array, $1)/ge;

use Data::Dumper;

print Dumper(\@array, \%hash);