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website/content/ChapterFour/0226.Invert-Binary-Tree.md

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+# [226. Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)
+
+## 题目
+
+Invert a binary tree.
+
+**Example**:
+
+Input:
+
+```
+
+     4
+   /   \
+  2     7
+ / \   / \
+1   3 6   9
+
+```
+
+Output:
+
+```
+
+     4
+   /   \
+  7     2
+ / \   / \
+9   6 3   1
+
+```
+
+Trivia:   
+
+This problem was inspired by this original tweet by Max Howell:
+
+>Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f*** off.
+ 
+
+## 题目大意
+
+"经典"的反转二叉树的问题。
+
+
+## 解题思路
+
+还是用递归来解决，先递归调用反转根节点的左孩子，然后递归调用反转根节点的右孩子，然后左右交换根节点的左孩子和右孩子。
+
+
+
+
+## 代码
+
+```go
+
+package leetcode
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func invertTree(root *TreeNode) *TreeNode {
+	if root == nil {
+		return nil
+	}
+	invertTree(root.Left)
+	invertTree(root.Right)
+	root.Left, root.Right = root.Right, root.Left
+	return root
+}
+
+```