Java 5 lines dfs
\n    public List<Integer> postorder(Node root) {\n        List<Integer> res = new ArrayList<>();\n        if (root == null) return res;\n        for (Node node
```\n    public List<Integer> postorder(Node root) {\n        List<Integer> res = new ArrayList<>();\n        if (root == null) return res;\n        for (Node node : root.children) for (int val : postorder(node)) res.add(val);\n        res.add(root.val);\n        return res;\n    }\n```
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