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

Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

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Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]


Example 2:

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]


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Constraints:


	The number of nodes in the tree is in the range [0, 104].
	0 &lt;= Node.val &lt;= 104
	The height of the n-ary tree is less than or equal to 1000.


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Follow up: Recursive solution is trivial, could you do it iteratively?

"""
# Definition for a Node.
class Node:
    def __init__(self, val=None, children=None):
        self.val = val
        self.children = children
"""

class Solution:
    def postorder(self, root: 'Node') -> List[int]:
        ans=[]
        def post(root):
            nonlocal ans
            if not root:
                return
            for i in root.children:
                post(i)
            ans.append(root.val)
        post(root)
        return ans
class Solution {
    List<Integer> result = new ArrayList<>();
    public List<Integer> postorder(Node root) {
        addNodes(root);
        return result;
    }
    
    void addNodes(Node root) {
        if (root == null) return;
        for (Node child : root.children) addNodes(child);
        result.add(root.val);
    }
}
 class Solution {
public:
    void solve(Node*root,vector<int>&ans){
        if(root==NULL)return;
        for(int i=0;i<root->children.size();i++){
            solve(root->children[i],ans);
        }
        ans.push_back(root->val);
    }
    vector<int> postorder(Node* root) {
        vector<int>ans;
        solve(root,ans);
        return ans;
    }
		
var postorder = function(root) {
    const res = [];
    function post(node) {
        if (!node) return;
        for (let child of node.children) {
            post(child);
        }
        res.push(node.val);
    }
    post(root);
    return res;
};
N-ary Tree Postorder Traversal