Brother, your typesetting really makes people have no desire to help you. And the json you posted is also in the wrong format, so it's even more impossible to help, so you'd better correct the typesetting of the problem first.

the brothers above have already answered it. I have another way of thinking. It can be regarded as the cool techs of php. You can also refer to

function formatSite($site_str) {
    
        $sites_info = explode('$$$', $site_str);

        $result = [];
        foreach ($sites_info as $site_info) {
            list($site_name, $info) = explode('$$', $site_info);

            array_map(function ($item) use (&$result, $site_name) {
                preg_match('/.*(\d).*\$(.*)\$(.*)/', $item, $matched);
                list($number, $site_link, $site_source) = array_slice($matched, 1);
                $result['sitePerEpisode'][$number][] = [
                    'siteSource'=>$site_source,
                    'siteName'=>$site_name,
                    'siteLink'=>$site_link
                ];
            }, explode('-sharp', $info));
        }
        return $result;
}

$str = '$$1$http://v.youku.com/$youku-sharp2$http://v.youku.com/v_show$youku-sharp3$http://v.youku.com/$youku$$$$$1$http://vmguo.com$mgtv-sharp2$http://v.mangguo.com$mgtv-sharp3$http://v.mangguo.com$mgtv';
$result = formatSite($str);

the train of thought is the same, and the logical brother's answer is clearer. I just used some cool techs

your variable $ceshi seems to be wrong. I changed it. I don't know if it's correct

//
$ceshi='$$1$http://v.youku.com/$youku-sharp2$http://v.youku.com/v_show$youku-sharp3$http://v.youku.com/$$$$$1$http://vmguo.com$mgtv-sharp2$http://v.mangguo.com$mgtv-sharp3$http://v.mangguo.com$mgtv';

//$youku
$ceshi='$$1$http://v.youku.com/$youku-sharp2$http://v.youku.com/v_show$youku-sharp3$http://v.youku.com/$youku$$$$$1$http://vmguo.com$mgtv-sharp2$http://v.mangguo.com$mgtv-sharp3$http://v.mangguo.com$mgtv';

$result_array = array();

$temp = explode('$$$',$ceshi);
//var_dump($temp);
foreach($temp as $key=>$value){

    $temp_array = (explode('$$',$value));
    //
    $category = $temp_array[0];
    //
    $temp_array = explode('-sharp',$temp_array[1]);
    foreach($temp_array as $key=>$value){
        
        //
        $temp_value = explode('$',$value);
        $ep_number = preg_replace('/()||()/','',$temp_value[0]);
        
        //
        $temp_result['siteSource']= $temp_value[2];
        $temp_result['siteName']= $category;
        $temp_result['siteLink']= $temp_value[1];
    
        //
        $result_array["sitePerEpisode"][$ep_number][]=$temp_result;

    }
}

//$result_arrayvar_dump
//var_dump($result_array);

//json
$json_result = json_encode($result_array,true);
echo $json_result;

array results not converted to json

array(1) {
  ["sitePerEpisode"]=>
  array(3) {
    [1]=>
    array(2) {
      [0]=>
      array(3) {
        ["siteSource"]=>
        string(5) "youku"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(19) "http://v.youku.com/"
      }
      [1]=>
      array(3) {
        ["siteSource"]=>
        string(4) "mgtv"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(16) "http://vmguo.com"
      }
    }
    [2]=>
    array(2) {
      [0]=>
      array(3) {
        ["siteSource"]=>
        string(5) "youku"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(25) "http://v.youku.com/v_show"
      }
      [1]=>
      array(3) {
        ["siteSource"]=>
        string(4) "mgtv"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(20) "http://v.mangguo.com"
      }
    }
    [3]=>
    array(2) {
      [0]=>
      array(3) {
        ["siteSource"]=>
        string(5) "youku"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(19) "http://v.youku.com/"
      }
      [1]=>
      array(3) {
        ["siteSource"]=>
        string(4) "mgtv"
        ["siteName"]=>
        string(12) ""
        ["siteLink"]=>
        string(20) "http://v.mangguo.com"
      }
    }
  }
}

traverses once is fine. You post the original PHP code you wrote.