php 实现字符串最大子串长度

求字符串最大子串长度
<?php
class zif
{
    public function sz($str)
    {
        $strsz = str_split($str);

        $zi = [];
        $len = [];
        foreach ($strsz as $val) {
            if (in_array($val, $zi)) {
                $c = count($zi);
                array_push($len, $c);
                $zi = [];
            }
            array_push($zi, $val);
        }
        if (!empty($zi)) {
            $c = count($zi);
            array_push($len, $c);
            $zi = [];
        }
        return max($len);
    }
}

$s = new zif();
$j = $s->sz('qwerghhjhn');
echo $j;