Python Iterative solution 40ms, faster than 98.76%
\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]:\n        if not root:\n            return []\n        s1 = []\n        s1.append(root)\
```\nclass Solution:\n    def postorder(self, root: \'Node\') -> List[int]:\n        if not root:\n            return []\n        s1 = []\n        s1.append(root)\n        s2=[]\n        while s1:\n            node = s1.pop()\n            s2.append(node.val)\n            s1.extend(node.children)\n        return reversed(s2)\n```
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