PHP 实现递归调用

$json='[
		{"id":9,"address":"上海","parent_id":0},
		{"id":1,"address":"安徽","parent_id":0},
		{"id":2,"address":"江苏","parent_id":0},
		{"id":3,"address":"合肥","parent_id":1},
		{"id":4,"address":"庐阳区","parent_id":3},
		{"id":5,"address":"大杨镇","parent_id":4},
		{"id":6,"address":"南京","parent_id":2},
		{"id":7,"address":"玄武区","parent_id":6},
		{"id":8,"address":"梅园新村街道","parent_id":7},
		{"id":16,"address":"梅园新村小区","parent_id":8},
		{"id":17,"address":"蔷薇园","parent_id":16},
		{"id":18,"address":"三号楼","parent_id":17},
		{"id":10,"address":"黄浦区","parent_id":9},
		{"id":11,"address":"外滩","parent_id":10},
		{"id":12,"address":"安庆","parent_id":1},
		{"id":13,"address":"浙江","parent_id":0},
		{"id":14,"address":"嘉兴","parent_id":13},
		{"id":15,"address":"河南","parent_id":0}
	]';

//首先这是字符串，需要转换成数组才能被调用
$json  = json_decode($json,true);
//打印下看看是不是数组，如果是，才能对其进行调研
print_r($json);

//定义一个函数城市树，里面传递参数
	function City_tree($json,$id,$step){
		//静态调用方法
		static $tree=[];
		//遍历出数组中的值
		foreach ($json as $key => $value){
			//数组的key值必须与id值相同
			if($value['parent_id']==$id){
				//添加拼接字符--
				$flg=str_repeat('--',$step);
				$value['address']=$flg.$value['address'];
				$tree[] = $value;
				//执行循环
				City_tree($json,$value['id'],$step+1);
			}
		}
		return $tree;
	}
	$tree = City_tree($json,0,0);
	foreach ($tree as $value1){
    	echo $value1['address'].'
';
	}

上海
--黄浦区
----外滩
安徽
--合肥
----庐阳区
------大杨镇
--安庆
江苏
--南京
----玄武区
------梅园新村街道
--------梅园新村小区
----------蔷薇园
------------三号楼
浙江
--嘉兴
河南