a perl print problem

gistfile1.pl

#./test.pl 2 4 5 8 12
#          *
#          *
#          *
#          *
#         **
#         **
#         **
#        ***
#       ****
#       ****
#      *****
#      ***** 

use 5.010;
use strict;
use warnings;
my @a = @ARGV;
unshift @a,0;

my @b =reverse  map {   $a[$_]-$a[$_-1] } 1..$#a ;
my $len = $ARGV[-1];

my $string ;

foreach my $t (@b)
{
    $string .= '*';
    next if $t == 0;
    my $line = ' 'x($len - length $string );
    print $line. $string ,"\n"  for 1..$t;
}