解法一：递归

递归进行后序遍历。

  1. /*
  2. // Definition for a Node.
  3. class Node {
  4.     public int val;
  5.     public List<Node> children;
  7.     public Node() {}
  9.     public Node(int _val) {
  10.         val = _val;
  11.     }
  13.     public Node(int _val, List<Node> _children) {
  14.         val = _val;
  15.         children = _children;
  16.     }
  17. };
  18. */
  20. class Solution {
  21.     private List<Integer> list;
  23.     public List<Integer> postorder(Node root) {
  24.         list = new LinkedList<>();
  25.         postOrder(root);
  26.         return list;
  27.     }
  29.     private void postOrder(Node root) {
  30.         if (root == null) {
  31.             return;
  32.         }
  33.         for (Node node : root.children) {
  34.             postOrder(node);
  35.         }
  36.         list.add(root.val);
  37.     }
  38. }