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### Re: Vampire Numbers

by particle (Vicar)
 on Jun 11, 2002 at 01:02 UTC ( #173355=note: print w/replies, xml ) Need Help??

i love these problems, YuckFoo. i think i should pick up one of these books you've been reading. i keep my skills sharp with martin gardner's puzzlers ( here's a book list. )

okay, so this code's a little evil :P

i should probably document it a bit.... here goes:

```#!/usr/bin/perl
use strict;
use warnings;
\$|++;

# is using Algorithm::FastPermute cheating? i hope not.
use Algorithm::FastPermute qw/ permute /;
## use Data::Dumper;                      # see what's inside...

( @ARGV == 2 and \$ARGV[0] < \$ARGV[1] ) # process arguments
? my( \$lower, \$upper ) = @ARGV
: die 'usage: ' . \$0 . ' lower upper' . \$/;

NUMBER: for my \$try ( \$lower..\$upper )
{ # try each number within bounds
my @digits = split //, '*' . \$try;   # makes ( '*', 1, 2, 3, etc )
my @permutations;                    # holds permutations

# push permutations onto array
#   unless the permutation has a '*' on either end
permute {
push @permutations, [ @digits ]
unless @digits->[-1] eq '*' or @digits->[0] eq '*';
} @digits;

## # uncomment to see what's inside...
##   print Dumper \@permutations;

my %results =                        # product => operation pairs
map { eval( \$_ ) || 0, \$_ }        #     create pair
map { join( '', @{ \$_ } ) }        #   stringify the array
@permutations;                     # for each permutation

## # uncomment to see what's inside...
##   print Dumper \@permutations;

defined \$results{ \$try }             # if i found one
&& print( \$try,                    # print it
' is vampire (',
\$results{ \$try },                # and how i got there
')', \$/ )
&& next NUMBER;
}

~Particle *accelerates*

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