สมมติมีเลข 1 2 3 5 8 9 11 ต้องการทำให้เป็น 1-3,5,8-9,11 ทำยังไงได้บ้างคะ

$string = "";
$number = array(1 ,2 ,3 ,5 ,8 ,9,10,11,12,13,17,20,22,23,24,29);
$max = count($number);
for($i=0; $i<$max; $i++){
	if($i <= $max-1)
	if($i>0 && ($number[$i-1]+1 == $number[$i]) && ($number[$i+1] == $number[$i]+1)){		
		if($string[strlen($string)-1] != '-')		
			$string .= "-";
	}elseif($i == 0 || ($i+1) == $max || $number[$i]+1 == $number[$i+1]){
		$string .= $number[$i];		
	}else{
		$string .= $number[$i].",";		
	}

}
echo implode(',' , $number);
echo "<br />";
echo $string;

<?php
    $array = array(1, 2, 3, 5, 8, 9, 10, 11, 12, 13, 17, 18, 20, 22, 23, 24, 29);

    echo implode(", ", $array);

    echo "<br /><br />";

    $result = array();
    $previous = 0;

    foreach ($array as $i) {
        if ($previous == 0) {
            $list = array();
            array_push($list, $i);
            $previous = $i;
        } else if ($i == $previous + 1) {
            array_push($list, $i);
            $previous = $i;
        } else {
            array_push($result, $list);
            unset($list);
            $list = array();
            array_push($list, $i);
            $previous = $i;
        }

        if ($i == max($array)) {
            array_push($result, $list);

            foreach ($result as $l) {
                if (count($l) == 1)
                    echo min($l);
                else
                    echo min($l) . '-' . max($l);

                if (max($l) < max($array))
                    echo ', ';
            }
        }
    }
?>