use strict;
use warnings;

my @a = (10, 15, -20, -30);
my $highest = abs($a[-1]);
my @full = (0) x ($highest + 1);

# decrement all negative values by 1, otherwise
# we would exclude the end points:
for (@a) {
    $_-- if $_ < 0;
}


my $count = 0;
for (0..$highest) {
    if (abs $a[0] == $_) {
        my $c = shift @a;
        if ($c > 0) {
            $count++;
        } else {
            $count--;
        }
    }
    $full[$_] += $count;
}

print join('', @full), "\n";