feat: add python and java solutions to lcof problem

添加《剑指 Offer题解》：面试题27. 二叉树的镜像

Author: yanglbme

README_CN.md

@@ -17,7 +17,7 @@
 ## 项目介绍
 本项目包含 [LeetCode](https://leetcode-cn.com/problemset/all/)、[《剑指 Offer（第 2 版）》](https://leetcode-cn.com/problemset/lcof/)、[《程序员面试金典（第 6 版）》](https://leetcode-cn.com/problemset/lcci/)等题目的相关题解。所有题解均由多种编程语言实现，包括但不限于：Java、Python、C++、JavaScript、C#、Go，日常更新。
 
-[English version here.](./README.md)
+[English Version](./README.md)
 
 ## 题解
 - [LeetCode](./solution/README.md)

lcof/面试题27. 二叉树的镜像/README.md

@@ -0,0 +1,88 @@
+# [面试题27. 二叉树的镜像](https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof/)
+
+## 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`
+
+## 解法
+### Python3
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def mirrorTree(self, root: TreeNode) -> TreeNode:
+        if root is None or (root.left is None and root.right is None):
+            return root
+            
+        self.mirrorTree(root.left)
+        self.mirrorTree(root.right)
+        root.left, root.right = root.right, root.left
+        return root
+```
+
+### Java
+```java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode mirrorTree(TreeNode root) {
+        if (root == null || (root.left == null && root.right == null)) {
+            return root;
+        }
+        mirrorTree(root.left);
+        mirrorTree(root.right);
+        TreeNode t = root.left;
+        root.left = root.right;
+        root.right = t;
+        return root;
+    }
+}
+```
+
+### ...
+```
+
+```

lcof/面试题27. 二叉树的镜像/Solution.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode mirrorTree(TreeNode root) {
+        if (root == null || (root.left == null && root.right == null)) {
+            return root;
+        }
+        mirrorTree(root.left);
+        mirrorTree(root.right);
+        TreeNode t = root.left;
+        root.left = root.right;
+        root.right = t;
+        return root;
+    }
+}

lcof/面试题27. 二叉树的镜像/Solution.py

@@ -0,0 +1,16 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution:
+    def mirrorTree(self, root: TreeNode) -> TreeNode:
+        if root is None or (root.left is None and root.right is None):
+            return root
+            
+        self.mirrorTree(root.left)
+        self.mirrorTree(root.right)
+        root.left, root.right = root.right, root.left
+        return root