php实现快速排序

function quick_sort(&$arr){
    _quick_sort($arr, 0, count($arr) -1);
}
function _quick_sort(&$arr, $start, $end){
    if($start >= $end){
        return;
    }
    $m = partition($arr, $start, $end);
    echo $m;
    _quick_sort($arr, $start, $m - 1);
    _quick_sort($arr, $m + 1, $end);
    
}
function partition(&$arr, $start, $end){
    $tmp = $arr[$start];
    while($start < $end){
        while ($start < $end &&  ($tmp <= $arr[$end])) {
            $end--;
        }
        swap($arr, $start, $end);
        while ($start < $end && ($arr[$start] <= $tmp) ) {
            $start++;
        }
        swap($arr, $start, $end);
    }
    return $start;
}
quick_sort($arr);