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Java-based LeetCode algorithm problem solutions, regularly updated

There is a newer version: 1.39

145\. Binary Tree Postorder Traversal

Easy

Given the `root` of a binary tree, return _the postorder traversal of its nodes' values_.

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/08/28/pre1.jpg)

**Input:** root = [1,null,2,3]

**Output:** [3,2,1] 

**Example 2:**

**Input:** root = []

**Output:** [] 

**Example 3:**

**Input:** root = [1]

**Output:** [1] 

**Example 4:**

![](https://assets.leetcode.com/uploads/2020/08/28/pre3.jpg)

**Input:** root = [1,2]

**Output:** [2,1] 

**Example 5:**

![](https://assets.leetcode.com/uploads/2020/08/28/pre2.jpg)

**Input:** root = [1,null,2]

**Output:** [2,1] 

**Constraints:**

*   The number of the nodes in the tree is in the range `[0, 100]`.
*   `-100 <= Node.val <= 100`

**Follow up:** Recursive solution is trivial, could you do it iteratively?