#!/usr/local/bin/perl -w
use strict;
$|=1;

my $vecPrime;
my %rotPrime;
# allows specification of a range, such as (1000, 9999)
my ($min, $max) = (2, 999_999);

print "---creating prime vector (length: $max)\n";
$vecPrime = createPrimeVec($max);
print "---created\n\n";

print "---trying rotations $min..$max\n";
for($min..$max) {
	next unless isprime($_);
	my $x = rotPrime($_);
	$x && $rotPrime{$x}++;
}
print "---tried $min..$max\n\n";
print "$_\n" for(sort {$a <=> $b} keys %rotPrime);

#----------
# return list of prime numbers up to and including value passed (default:1000)
sub createPrimeVec {
    my $UPPER = shift || 1000;
    my $sieve = "";
    GUESS: for (my $guess = 2; $guess <= $UPPER; $guess++) {
		next GUESS if vec($sieve,$guess,1);
		for(my $mults = $guess * $guess; $mults <= $UPPER; $mults += $guess) {
			vec($sieve,$mults,1) = 1;
    }	}
	return $sieve;
};

# returns true if found in prime number bit vector
sub isprime { return 1 if( vec($vecPrime,shift,1) == 0 ); };

# return smallest 'rotationally prime' number in set
# for instance, 1931, 9311, 3119, or 1193 yeilds return value 1193
sub rotPrime {
	my ($num, $lchr, @list) = (shift);
	for(1..length $num) {
		$lchr = chop $num;
		$num = $lchr . $num;
		push @list, $num;
		return unless isprime($num);
	}
	return (sort @list)[0];
};