Iterative Python solution using stack
\nclass Solution(object):\n    def postorder(self, root):\n        """\n        :type root: Node\n        :rtype: List[int]\n        """\n        \n        outp
```\nclass Solution(object):\n    def postorder(self, root):\n        """\n        :type root: Node\n        :rtype: List[int]\n        """\n        \n        output = []\n        stack = [root]\n        \n        if not root:\n            return output\n        \n        while stack:\n            last = stack.pop()\n            stack += last.children\n            output += [last.val]\n        \n        return output[::-1] # reverse the output before returning\n```
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