Easiest C#12 recursive solution
Code\n\npublic class Solution {\n    public IList<int> Postorder(Node root) => root switch {\n        null => [],\n        _ => [..root.children.SelectMany(Post
# Code\n```\npublic class Solution {\n    public IList<int> Postorder(Node root) => root switch {\n        null => [],\n        _ => [..root.children.SelectMany(Postorder), root.val]\n    };\n}\n```
['C#']