Display based on __DATA__
     SNO   A  B  C  D
num: 1011  X  X  X  X
num: 0001  X  X  X  X
num: 0011  X  X  X  X
num: 0201  X  X  X  X
num:
num:
...

##</code><code>##

use strict;
use Data::Dumper;

my @display = (); # AoA
while (<DATA>) {
	build_display($_);
}

print "     SNO   A  B  C  D\n";
for (@display) {
	print 'num: ' . join('  ', @$_) . "\n";
}
print "\n";


##########################
sub build_display {
##########################
	my $serialno = shift;
	chomp $serialno;
	if ($serialno) {
		my ($prefix,$number) = ($serialno =~ /^(\w)(\w{4})/);
		my $j = ($prefix =~ /A/i) ? 1
			  : ($prefix =~ /B/i) ? 2
			  : ($prefix =~ /C/i) ? 3
			  : ($prefix =~ /D/i) ? 4 : 0;

		my $temp = '';
		for (0..$#display) {
			if ($display[$_][0] =~ /^$number$/i) {  ## Need to update array_ref
				$temp = $display[$_];     ## copy to temp
				splice(@display, $_, 1);  ## delete from array. Added to top later.
print "After Delete: " . Dumper(\@display); <stdin>;
			}
		}
## ?? Adds an element to the @display array if update is required. But why OR how ?? 
print "Before Add: " . Dumper(\@display); <stdin>;
		## if 'number' not in array, create a new entry.
		$temp = [$number,' ',' ',' ',' '] if (!$temp);

		$temp->[$j] = 'X'; ## flag the applicable prefix
		unshift @display, $temp;  ## add to top of array.
	}
}

__DATA__
A0011
B0001
C0201
D0001
A1011
B0201
C1011
D0201
A0201
B0011
C0011
D0011
A0001
B1011
C0001
D1011