check duplicate value exists in array

<?php
$a = array(1,2,3,4,1,2,3,4);
$b = array(1,2,3,4,5,6,7);

echo '<br','>$a=';
if (count(array_unique($a)) == count($a)){
 echo 'not duplicate';
} else {
 echo 'duplicate';
}

echo '<br','>$b=';
if (count(array_unique($b)) == count($b)){
 echo 'not duplicate';
} else {
 echo 'duplicate';
}

?>