# 27.二叉树的镜像

## 题目描述

请完成一个函数，输入一个二叉树，该函数输出它的镜像。

例如输入：

```
      4
    /   \
   2     7
  / \   / \
 1   3 6   9
```

镜像输出：

```
      4
    /   \
   7     2
  / \   / \
 9   6 3   1
```

示例 1：

输入：root = \[4,2,7,1,3,6,9] 输出：\[4,7,2,9,6,3,1]

限制：

0 <= 节点个数 <= 1000

注意：本题与主站 226 题相同：<https://leetcode-cn.com/problems/invert-binary-tree/>

来源：力扣（LeetCode） 链接：<https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof> 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

## 题解一

递归

```swift
func mirrorTree(_ root: TreeNode?) -> TreeNode? {
    if root == nil {
        return nil
    }
    let left = root?.left
    let right = root?.right
    root?.left = mirrorTree(right)
    root?.right = mirrorTree(left)
    return root
}
```

## 题解二

stack

```swift
 func mirrorTree2(_ root: TreeNode?) -> TreeNode? {
    var stack: [TreeNode?] = [root]

    while stack.last != nil {
        let node = stack.removeLast()
        let right = node?.right
        let left = node?.left

        if let rn = right {
            stack.append(rn)
        }
        if let ln = left {
            stack.append(ln)
        }

        node?.left = right
        node?.right = left
    }

    return root
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://ryukiedev.gitbook.io/wiki/shu-ju-jie-gou-yu-suan-fa/jian-zhi-offerswift/27.-er-cha-shu-de-jing-xiang.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.