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root of an n-ary tree, return the postorder traversal of its nodes' values.
Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)
Input: root = [1,null,3,2,4,null,5,6] Output: [5,6,3,2,4,1]
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14] Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]
- The number of nodes in the tree is in the range
0 <= Node.val <= 104
- The height of the n-ary tree is less than or equal to
Follow up: Recursive solution is trivial, could you do it iteratively?