A simple approach would be to build two hashes from the strings, and then compare the hashes.

So you might do something like:

my %foo;
my $string = 'Poet Blake had a milky white cat. He used to call it Pus
+sy.';
for my $word (split /\s+/, $string) {
   $foo{$word}++;
}
[download]

You do the same for the second string, and then to compare you simply iterate through one of the hashes and increment a counter if each word is present in the other hash. Something like so:

my $cnt;
for my $word (keys %foo) {
    $cnt++ if $bar{$word};
}
[download]

To find the total number of words in either string, you simply count the number of keys in the hash, e.g.

my $word_count = scalar keys %foo;
[download]

And then it's just a simple calculation.
Obvious question is how does your calculation look if the two strings contain a different number of words? But I'm sure you can decide that.

hope this helps,
Darren

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