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

my %things = (
  "apple" => ["red", "round", "plant", "fruit"],
  "orange" => ["orange", "round", "plant", "fruit"],
  "pumpkin" => ["orange", "round", "plant", "vegetable"],
  "ball" => ["red", "round", "toy"],
);

my %kinds;

# 
# here we populate %kinds hash with kinds from %things, but of course 
# in real life we should do it while populating %things hash
# 
foreach my $t (keys %things) {
    foreach my $k (@{$things{$t}}) {
        $kinds{$k}{$t} = 1;
    }
}

# search for "red round plant"

my @search = split (' ',"red round plant");

my %kinds_slice;

# 
# we can use slice here only because kinds are strings
# if your kinds are not strings - well, it's another story
# 

@kinds_slice{@search} = @kinds{@search};

my %things_sort;

# 
# this is boring "count it" loop, but hey, 
# we're counting only %kinds_slice, not the whole/all %kinds! 
# 

foreach my $kind (keys %kinds_slice) {
    foreach my $thing (keys %{ $kinds_slice{$kind} }) {
        $things_sort{$thing}++;
    }
}

#
# all things that match search, sorted 
# 

print "Matches:\n",join ("\n",map {"$_: $things_sort{$_}"} sort { $things_sort{$b} <=> $things_sort{$a} } keys %things_sort),"\n\n";

# 
# or just get the first value to get best match
# 

my @matches = sort { $things_sort{$b} <=> $things_sort{$a} } keys %things_sort ;

print "Best match: ".$matches[0]."\n Score: ".$things_sort{$matches[0]}."\n";