#!/usr/bin/perl -w --
use strict;

# Usage: ./Pattern [n [string]]


##</code><code>##

my $depth = shift || 2;
my $string = shift || "helloworldhellohellohihellohiworld";
$string =~ s/[\000-\037\0177]/ /g; # strip non-printable

##</code><code>##

# seed dictionary with printable characters...
my %dict = map {(chr$_ => 0)} '32'..'126';
# and populate it from the input string
for (1..$depth) {
    my $j = '';
    for (split //, $string) {
        my $tmp = $j . $_;
        $j = defined $dict{$tmp} ? $tmp
            : do{
                $dict{$j}++;
                $dict{$tmp}=0;
                $_};
    }
}


##</code><code>##

# the following sort routine is arbitrary,
# chosen because it behaves the way I want... sort of.
{
    local $, = " ";
    local $\ = "\n";
    print sort {
        $dict{$a}*length($a)**2 <=> $dict{$b}*length($b)**2 #||
        } grep {length$_>1} keys %dict;
}

#use Data::Dumper;
#print Dumper(\%dict);

__END__

##</code><code>##

ow ohi llo worl dh ldh orl rld hellohi hi hellow lohi iwo ihe ell ld he ll lo iw rl oh ih el or wo hel wor loh hell helloh hello