590. N-ary Tree Postorder Traversal

题目描述：

Given an n-ary tree, return the postorder traversal of its nodes' values.

For example, given a 3-ary tree:

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

解题思路：

递归方法后序排序。

代码：

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<int> postorder(Node* root) {
        vector<int> ret;
        ret.reserve(1000);
        post(root, ret);
        return ret;
    }
    void post(Node* root, vector<int>& ret) {
        if (root == NULL)
            return;
        for (auto node : root->children) {
            post(node, ret);
        }
        ret.push_back(root->val);
    }
};