给定一个 N 叉树，返回其节点值的后序遍历。

例如，给定一个 3叉树 :

 

 

返回其后序遍历: [5,6,3,2,4,1].

 

 

/*// Definition for a Node.class Node {    public int val;    public List
     
       children;    public Node() {}    public Node(int _val,List
      
        _children) {        val = _val;        children = _children;    }};*/class Solution {    List
       
         list = new ArrayList<>();    public List
        
          postorder(Node root) {        if(root==null){
   return list;}        scanPre(root);        list.add(root.val);        return list;    }    public void scanPre(Node node){        if(node.children.size()==0){
   return;}        if(node.children.size()>0){            for(Node n:node.children){                scanPre(n);                list.add(n.val);            }        }    }}