List::Compare will also solve this problem.

#!/usr/bin/perl
use strict;
use warnings;
use 5.014;
use List::Compare;

my @winners=("ruth","sheila");
my @correct=("ruth","martin","dee","zack");

my $lc = List::Compare->new(\@winners, \@correct);

my @composite = $lc->get_Ronly;

print "@composite\n";
[download]

Prints
dee martin zack

Chris