Two Search Method

 private function sel($n) {
        $ls = range(1,999999);
        $min = 1;
        $max = count($ls);
        $mid = 0;
        $r   = '';
        while ($min<$max) {
            $mid = intval(($min+$max) / 2);

            switch ($ls[$mid]<=>$n) {
                case -1:
                    $max = $mid-1;
                    break;
                case 1:
                    $max = $mid+1;
                    break;
                case 0:
                    return $r = $ls[$mid];
                    break;
            }
        }
        return $r;
    }