package code; import java.util.ArrayList; import java.util.List; public class lc590 { class Node { public int val; public List children; public Node() {} public Node(int _val,List _children) { val = _val; children = _children; } } List res; public List postorder(Node root) { res = new ArrayList<>(); helper(root); return res; } public void helper(Node root){ if(root==null) return; for(Node nd:root.children){ helper(nd); } res.add(root.val); } }