use strict;
use warnings;

my @array=qw ( 1 2 3 10 11 12 13 20 21);
my $bin = 10;
my %hist;

map {	$hist{ (int(($_-1)/$bin)+1)*$bin }++ } @array;
print join ",", map { ($_-9)."-$_ $hist{$_}" } sort keys %hist;