給定一個 N 叉樹，返回其節點值的後序遍歷。

例如，給定一個3叉樹:

返回其後序遍歷:[5,6,3,2,4,1].

遞迴

"""
# 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]:
        res
 
=[]
        def helper(root):
            if not root:
                return None
            children=root.children
            for i in children:
                helper(i)
            res.append(root.val)
        helper(root)
        return res

迭代

"""
# 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]:
        if not root:
            return []
        res=[]
        stack=[root]
        while stack:
            node=stack.pop()
            res.append(node.val)
            for i in node.children:
                stack.append(i)
        
 
return res[::-1]