{
            $visible++;
            syswrite STDOUT, $forest[$current][$i] . 'V';
            usleep 100000;
            next;
        }
##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use List::Util qw{ none any };

# parse the input (piped in, or from filename on command line)
my @a = map { chomp; [ split // ] } <>;

# determine the dimensions
my $ni = @a;
my $nj = @{ $a[0] };

# sanity check
die "mismatched lengths" if any { @$_ != $nj } @a;

# assume all visible to start with
my $v = $ni * $nj;
for my $i (0 .. $ni - 1) {
  for my $j (0 .. $nj - 1) {
    my $t = $a[$i][$j];  # target
    next if none { $_ >= $t } map $a[$i][$_], 0 .. $j - 1;       # look left
    next if none { $_ >= $t } map $a[$i][$_], $j + 1 .. $nj - 1; # look right
    next if none { $_ >= $t } map $a[$_][$j], 0 .. $i - 1;       # look up
    next if none { $_ >= $t } map $a[$_][$j], $i + 1 .. $ni - 1; # look down

    # if not visible in any direction, then invisible
    --$v;
  }
}
print "Visible $v of $ni x $nj\n";