# Strict
use strict;
use warnings;

# Libraries;
use Data::Dumper;


# Main program
$| = 1;
my $phash = { };
my $parray = [ ];
my $ndiff = 0;

# Save all single characters and character pairs as hash keys
for (my $i = 0; $i < 256; $i++) {
    save_to_hash_and_array($i);
    for (my $j = 0; $j < 256; $j++) {
        save_to_hash_and_array($i, $j);
    }
}

# Test all single characters
for (my $i = 0; $i < 256; $i++) {
    my $is_same = hash_matches_array($i)? 1: 0;
    $is_same or $ndiff++;
    printf "%s", $is_same? ".": "@";
}
print "\n\n";

# Test all character pairs
for (my $i = 0; $i < 256; $i++) {
    for (my $j = 0; $j < 256; $j++) {
        my $is_same = hash_matches_array($i, $j)? 1: 0;
        $is_same or $ndiff++;
        printf "%s", $is_same? ".": "@";
    }
}
print "\n\n";
print "Number of mismatches = $ndiff\n";

# Uncomment out this line to see a lot of strange character
print "Type [RETURN] to see a dump of the hash ... ";
<STDIN>;
print Dumper($phash), "\n";


sub save_to_hash_and_array {
    my ($idx0, $idx1) = @_;
    my $key = chr($idx0);
    defined($idx1) and $key .= chr($idx1);
    my $value = sprintf "(%s:%s)", $idx0, ($idx1 || "blank");
    $phash->{$key} = $value;
    $parray->[$idx0 + 256*($idx1||0)] = $value;
}


sub hash_matches_array {
    my ($idx0, $idx1) = @_;
    my $key = chr($idx0);
    defined($idx1) and $key .= chr($idx1);
    my $hval = $phash->{$key};
    my $aval = $parray->[$idx0 + 256*($idx1||0)];
    return ($hval eq $aval)? 1: 0;
}