Update 二叉树相关.md

blogs/Algorithm/剑指 Offer/二叉树相关.md

@@ -89,3 +89,47 @@ class Solution {
 }
 ```
 
+#### [ 27. 二叉树的镜像](https://leetcode-cn.com/problems/er-cha-shu-de-jing-xiang-lcof/)
+
+```java
+class Solution {
+
+    public TreeNode mirrorTree(TreeNode root) {
+        if (root == null) {
+            return null;
+        }
+        TreeNode rootLeft = mirrorTree(root.right);
+        TreeNode rootRight = mirrorTree(root.left);
+        root.left = rootLeft;
+        root.right = rootRight;
+        return root;
+    }
+}
+```
+
+```java
+class Solution {
+
+    public TreeNode mirrorTree(TreeNode root) {
+        if (root == null) {
+            return null;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        stack.add(root);
+        while (!stack.isEmpty()) {
+            TreeNode node = stack.pop();
+			if (node.left != null) {
+				stack.add(node.left);
+			}
+			if (node.right != null) {
+				stack.add(node.right);
+			}
+            TreeNode temp = node.left;
+            node.left = node.right;
+            node.right = temp;
+        }
+        return root;
+    }
+}
+```
+