Check if array contains a duplicate value in string with PHP

I want to check if my array contains a duplicate value. I have a form where i pass a Chapter ID with the following method:

<input name="chapter_id[]" type="number" value="<?= $row_chapter_list['chapter_id'] ?>">

To update my database i pick this input and do the update w/o any issues:

if (isset($_POST['chapter_id'])) {
 
  // Update Kapitelnummer
  $statement = $pdo->prepare("UPDATE questionaire_chapter SET chapter_id = :chapter_id WHERE id = :id");
  $statement->bindParam(":chapter_id", $chapter_id, PDO::PARAM_STR);
  $statement->bindParam(":id", $id, PDO::PARAM_INT);
  foreach ($_POST['chapter_id'] as $index => $chapter_id) {
    $id = $_POST['chapter_inc_id'][$index];
    $statement->execute();
  }     
}

A typical var_dump result looks like:

array(3) { [0]=> string(1) "1" [1]=> string(2) "12" [2]=> string(2) "12" }

In this array example the value "12" is present in two strings. I would like to create a mechanic to count double values and and use the result in a PHP if/else. i want to avoid that the a duplicate chapter ID gets written into my database.

My first try to count the string is this:

print_r(array_count_values($_POST['chapter_id']));

Which gives me a result like this

Array ( [1] => 1 [12] => 2 )

Now i am missing the method to implement a if else to check if the result is not 1.
Any idea how to do this?

>Solution :

You can use array_unique() to get an array where any duplicates has been filtered out. Using that, you can compare it to the original array:

if ($array != array_unique($array)) {
    echo "The arrays are not the same, which means that there are duplicates";
}