解法一

前序遍历。

  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.     List<Integer> ans;
  22.     public List<Integer> preorder(Node root) {
  23.         ans = new LinkedList<>();
  24.         preOrder(root);
  25.         return ans;
  26.     }
  28.     private void preOrder(Node root) {
  29.         if (root == null) {
  30.             return;
  31.         }
  32.         ans.add(root.val);
  33.         for (Node child : root.children){
  34.             preOrder(child);
  35.         }
  36.     }
  37. }