#!/usr/bin/perl
use strict;
use warnings;

my @x = qw (hi there hello there hello world);
my @y = qw (hi there hello new element there there);

my (%xh,%yh) = ();

# count the number of repeats in each array
$xh{$_}++ for (@x); 
$yh{$_}++ for (@y);

my $common = 0;

# for all keys in the hash check if it exists in the other hash. if it does then choose the min of the two for number of repeats.
for (keys %xh) {
    $common += min($xh{$_}, $yh{$_}) if (exists($yh{$_}));
}

print "Number common = $common\n";

sub min {
    return (($_[0] <= $_[1]) ? $_[0] : $_[1]);
}