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docs/notes/27. 二叉树的镜像.md

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+# 27. 二叉树的镜像
+
+[NowCoder](https://www.nowcoder.com/practice/564f4c26aa584921bc75623e48ca3011?tpId=13&tqId=11171&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+
+## 题目描述
+
+<img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/0c12221f-729e-4c22-b0ba-0dfc909f8adf.jpg" width="300"/>
+
+## 解题思路
+
+```java
+public void Mirror(TreeNode root) {
+    if (root == null)
+        return;
+    swap(root);
+    Mirror(root.left);
+    Mirror(root.right);
+}
+
+private void swap(TreeNode root) {
+    TreeNode t = root.left;
+    root.left = root.right;
+    root.right = t;
+}
+```