Easy & Fast Solution Python 3
\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]: \n        ans=[]\n        if not root:\n            return []\n        def cal(r:\'Node
```\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]: \n        ans=[]\n        if not root:\n            return []\n        def cal(r:\'Node\')->List[int]:\n            ans.append(r.val)\n            if r.children:\n                for i in range(len(r.children)-1,-1,-1):\n                    cal(r.children[i])\n        cal(root)   \n        ans.reverse()\n        return ans    \n```
['Python', 'Python3']