#! /usr/bin/perl

use strict ;

use Algorithm::Permute ;
use Data::Dumper ;

my @words_raw = qw/ receding hairline bald / ;

# First, check for & remove duplicate words in the list.
my @words = () ;
{
    my %wc = () ;
    foreach ( @words_raw )
    {
        push @words, $_ unless $wc{$_}++ ;
    }
}

# Cardinality of powerset of @words = 2**n,
# where n = |@words|.
my $cardinality = 2 ** @words ;
my $places      = ( log( $cardinality ) / log( 2 ) ) ;

# Generate binary templates for all subsets of @words.
my $fmt_str       = "%0${places}b" ;
my @set_templates = map { sprintf $fmt_str, $_ }
                    ( 0 .. $cardinality - 1 ) ;

my @power_set = () ;

# Replace the template values with the contents of @words.
# This will form the power set of @words.
foreach ( @set_templates )
{
    my @flags = split // ;
    my @temp_set = () ;
    for ( my $i = 0 ; $i < @flags ; $i++ )
    {
        push @temp_set, $words[$i] if $flags[$i] ;
    }
    push @power_set, \@temp_set ;
}

my @all_iterations = () ;

# Drop the empty set from the power set (it's irrelevant
# in the context of a search engine.
shift @power_set ;

# Find the set of possible permutations for each set in
# the power set of @words.
foreach my $set ( @power_set )
{
    my $p = new Algorithm::Permute $set ;
    while ( my @res = $p->next )
    {
        push @all_iterations, join ' ', @res ;
    }
}

# Voila!
print Dumper( \@all_iterations ) ;
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