590. N叉树的后序遍历

给定一个 N 叉树，返回其节点值的后序遍历。

例如，给定一个 3叉树 :

返回其后序遍历: [5,6,3,2,4,1].

递归

"""
# 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]