# 226 Invert Binary Tree

## 226. Invert Binary Tree

## 1. Question

Invert a binary tree.

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

to

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

## 2. Implementation

**(1) DFS**

```java
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }

        TreeNode left = root.left;
        TreeNode right = root.right;
        root.left = invertTree(right);
        root.right = invertTree(left);
        return root;
    }
}
```

**（2） BFS**

```java
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }

        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode curNode = queue.remove();
                TreeNode temp = curNode.left;
                curNode.left = curNode.right;
                curNode.right = temp;

                if (curNode.left != null) {
                    queue.add(curNode.left);
                }

                if (curNode.right != null) {
                    queue.add(curNode.right);
                }
            }
        }
        return root;
    }
}
```

## 3. Time & Space Complexity

DFS: 时间复杂度: O(n), 空间复杂度O(n), 平均复杂度是O(logn), 当树是平衡的时候

BFS: 时间复杂度: O(n), 空间复杂度O(w), w为一行中node最多的个数


---

# 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://protegejj.gitbook.io/my-algorithm-summary/data-structure/tree/226-invert-binary-tree.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.