#!/usr/bin/perl -w
use strict;
use Getopt::Std;
use vars qw/ $opt_h /;
$|++;

getopts("h");

my @letters = ( 'a' .. 'z' );
&fisher_yates_shuffle(\@letters);
my %caeser = map { $_ => shift @letters } 'a' .. 'z';
my %used;

while ( $_ = <> ) {
	tr/A-Z/a-z/;
	s/(.)/exists $caeser{$1} && ++$used{$1} && $caeser{$1} || $1/eg;
	print;
}

if ( $opt_h ) {
	my @used = keys %used;
	&fisher_yates_shuffle(\@used);
	my($hint)= shift @used;
	print "\nHint: ",$caeser{$hint},"=$hint\n";
}

sub fisher_yates_shuffle {
    my $array = shift;
    my $i;
    for ($i = @$array; --$i; ) {
        my $j = int rand ($i+1);
        next if $i == $j;
        @$array[$i,$j] = @$array[$j,$i];
    }
}