#!/perl -w
use strict;

$|=1;

my @cubes = ('pgpygr', 'rprrgy', 'ppryyg', 'rrygpy');

foreach my $c1perm (permuate_colours($cubes[0])) {
	foreach my $c2perm (permuate_colours($cubes[1])) {
		foreach my $c3perm (permuate_colours($cubes[2])) {
			foreach my $c4perm (permuate_colours($cubes[3])) {
				if ( validate($c1perm, $c2perm, $c3perm, $c4perm) ) {
					print "Solution: $c1perm, $c2perm, $c3perm, $c4perm\n";
				}
			}
		}
	}
}

sub validate {
	my (@colours) = @_;
	my %seen;
	foreach my $row (0..3) {
		foreach my $cube (0..3) {
			my $side_colour = substr($colours[$cube], $row, 1);
			if (exists $seen{$row}{$side_colour}) {
				return 0;
			}
			$seen{$row}{$side_colour}++;
		}
	}
	return 1;
}

sub permuate_colours {
	my ($colours) = @_;
	my @perms;
	for (1..4) {
		for (1..4) {
			push(@perms, $colours);
			$colours =~ s/(.)(.)(.)(.)(.)(.)/$2$3$4$1$5$6/; # spin
		}
		$colours =~ s/(.)(.)(.)(.)(.)(.)/$1$6$3$5$2$4/; # roll
	}

	$colours =~ s/(.)(.)(.)(.)(.)(.)/$2$3$4$1$5$6/; # spin
	$colours =~ s/(.)(.)(.)(.)(.)(.)/$1$6$3$5$2$4/; # roll
	for (1..4) {
		push(@perms, $colours);
		$colours =~ s/(.)(.)(.)(.)(.)(.)/$2$3$4$1$5$6/; # spin
	}
	$colours =~ s/(.)(.)(.)(.)(.)(.)/$1$6$3$5$2$4/; # roll
	$colours =~ s/(.)(.)(.)(.)(.)(.)/$1$6$3$5$2$4/; # roll
	for (1..4) {
		push(@perms, $colours);
		$colours =~ s/(.)(.)(.)(.)(.)(.)/$2$3$4$1$5$6/; # spin
	}
	return @perms;
}