// Given two integer arrays nums1 and nums2, return an array of their intersection. // Each element in the result must be unique and you may return the result in any order.

function intersection($nums1, $nums2) {
    // firstly, remove duplicates, 
    // you can use here array_unique function twice !
    $result1 = [];
    $result2 = [];
    foreach ($nums1 as $num1) {
    	if (!in_array($num1, $result1)) {
    		$result1[] = $num1;
        }
    }
    foreach ($nums2 as $num2) {
    	if (!in_array($num2, $result2)) {
    		$result2[] = $num2;
        }    
    }
    // merge two arrays
    // you can use here array_merge function !
    for ($i = 0;  $i < count($result2);  $i++) {
        $result1[$i + count($result1)] = $result2[$i];
    }
    $array = [];
    // unfortunately, I could not count the values ​​and 
    // get the keys from array without built-in function
    $result1 = array_count_values($result1);
    foreach ($result1 as $key => $value) {
    	if ($value >= 2) {
    		$array[] = $key;
    	}
    }
    return $array;
}
print_r(intersection([4, 9, 5], [9, 4, 9, 8, 4]));   // [4, 9];

// Instead of so much effort, you can just use the array_intersect() function.