N-aryTreePostorderTraversal*

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/*
// 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> vector;
        postorder(root, vector);
        return vector;
    }
    void postorder(Node* root, vector<int> &vector) {
        if (!root) return;
        for (auto node : root->children) {
            postorder(node, vector);
        }
        vector.push_back(root->val);
    }
};
/////////
  vector<int> postorder(Node* root) {
        if (!root) return {};
        vector<int> vector;
        stack<Node*> s{{ root }};
        while (!s.empty()) {
            Node *node = s.top();
            s.pop();
            vector.insert(vector.begin(), node->val);
            for (int i = 0; i < node->children.size(); i ++) {
                s.push(node->children[i]);
            }
        }
        return vector;
    }