更新了[lcof-27.二叉树的镜像]中的cpp版本题解 (#340)

* 更新了[lcof-27.二叉树的镜像]中的cpp版本题解

* 添加了[lcof-27.二叉树镜像]对应的readme文件

Co-authored-by: junfeng.fj <junfeng.fj@alibaba-inc.com>

Author: ChunelFeng

lcof/面试题27. 二叉树的镜像/README.md

@@ -129,6 +129,37 @@ func mirrorTree(root *TreeNode) *TreeNode {
 }
 ```
 
+### **C++**
+
+```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Solution {
+public:
+    TreeNode* mirrorTree(TreeNode* root) {
+        // 后续遍历
+        if (nullptr == root) {
+            return nullptr;
+        }
+
+        mirrorTree(root->left);
+        mirrorTree(root->right);
+        std::swap(root->left, root->right);
+
+        return root;
+    }
+};
+
+```
+
 ### **...**
 
 ```

lcof/面试题27. 二叉树的镜像/Solution.cpp

@@ -0,0 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Solution {
+public:
+    TreeNode* mirrorTree(TreeNode* root) {
+        // 后续遍历
+        if (nullptr == root) {
+            return nullptr;
+        }
+
+        mirrorTree(root->left);
+        mirrorTree(root->right);
+        std::swap(root->left, root->right);
+
+        return root;
+
+    }
+};

lcof/面试题55 - II. 平衡二叉树/Solution.cpp

@@ -31,7 +31,7 @@ class Solution {
             }
         }
 
-        return false;    // 如果
+        return false;    // 如果有一处已经确定不是平衡二叉树了，则直接返回false
     }
 
     bool isBalanced(TreeNode* root) {