message: Update diameter-of-n-ary-tree.cpp
diff: // Time: O(n)
  // Space: O(h)
  -/*
  -// Definition for a Node.
  -class Node {
  -public:
  - int val;
  - vector<Node*> children;
  -
  - Node() {}
  -
  - Node(int _val) {
  - val = _val;
  - }
  -
  - Node(int _val, vector<Node*> _children) {
  - val = _val;
  - children = _children;
  - }
  -};
  -*/
  -
  -// Time: O(n)
  -// Space: O(h)
  -class Solution2 {
  +class Solution {
  public:
  int diameter(Node* root) {
  return iter_dfs(root).first;
  