PHP quick sort problem

As shown in the picture: PHP quick method, two writing methods in the loop, the above one is OK, the following one will report errors;

Error screenshot:

Reply content:

As shown in the picture: PHP quick method, two writing methods in the loop, the above one is OK, the following one will report errors;

Error screenshot:

Did you think

<code>if ($v > $mid) {
    $rightArr[] = $v;
}
if ($v < $mid) {
    $leftArr[] = $v;
}</code>

and

<code>if ($v < $mid) {
    $leftArr[] = $v;
} else {
    $rightArr[] = $v;
}</code>

Does it mean the same thing?

Don’t you consider the situation where $v == $mid?