public class Solution extends Object
145 - Binary Tree Postorder Traversal.
Easy
Given the root of a binary tree, return the postorder traversal of its nodes’ values.
Example 1:

Input: root = [1,null,2,3]
Output: [3,2,1]
Example 2:
Input: root = []
Output: []
Example 3:
Input: root = [1]
Output: [1]
Example 4:

Input: root = [1,2]
Output: [2,1]
Example 5:

Input: root = [1,null,2]
Output: [2,1]
Constraints:
[0, 100].-100 <= Node.val <= 100Follow up: Recursive solution is trivial, could you do it iteratively?
| Constructor and Description |
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Solution() |
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