【LeetCode】590. N-ary Tree Postorder Traversal

题目链接：https://leetcode.com/problems/n-ary-tree-postorder-traversal/

For example, given a 3-ary tree:

 

 

Return its postorder traversal as: [5,6,3,2,4,1].

 

Note:

Recursive solution is trivial, could you do it iteratively?

N叉树的后序遍历。
方法一递归：

class Solution {
public:
    vector<int> ans;
    vector<int> postorder(Node* root) {
        if(!root)return ans;
        for(int i=0;i<root->children.size();i++){
            postorder(root->children[i]);  
        }
        ans.push_back(root->val);
        return ans; 
    }   
};

题目中Note说能不能用迭代去做，所以又研究了一下迭代的方法。
方法二：

class Solution {
public:
    vector<int> ans;
    vector<int> postorder(Node* root) {
        stack<Node*> stk;
        if(!root)return ans;
        stk.push(root);
        while(!stk.empty()){
            Node* nod=stk.top();
            stk.pop();
            int len=nod->children.size();
            for(int i=0;i<len;i++){
                stk.push(nod->children[i]);
            }
            ans.push_back(nod->val);
        }
        reverse(ans.begin(),ans.end());
        return ans; 
    }   
};