# \[94]\[中等] 二叉树的中序遍历

## 题目描述

[94. 二叉树的中序遍历](https://leetcode-cn.com/problems/binary-tree-inorder-traversal/)

给定一个二叉树，返回它的中序 遍历。

示例:

```
输入: [1,null,2,3]
   1
    \
     2
    /
   3

输出: [1,3,2]
```

进阶: 递归算法很简单，你可以通过迭代算法完成吗？

## 解题思路

### 递归

```python
class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        res = []

        def dfs(node):
            if node is None:
                return

            dfs(node.left)
            res.append(node.val)
            dfs(node.right)

        dfs(root)
        return res
```

### 迭代

```python
class Solution:
    def inorderTraversal(self, root: TreeNode) -> List[int]:
        res, stack = [], []
        node = root

        while node is not None or stack:
            while node:
                stack.append(node)
                node = node.left

            if stack:
                node = stack.pop(-1)
                res.append(node.val)
                node = node.right
        return res
```


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