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+# [226. Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/description/)
+# 思路
+翻转二叉树。    
+递归算法的话很简单:
+* 若为空树则返回空即可。
+* 令左子树指向翻转后的右子树，将右子树指向翻转后的左子树。
+
+非递归算法的话用先方向层序遍历(从右到左从上到下)，然后再正常层序重新赋值即可。
+# C++
+``` C++
+class Solution {
+public:
+    TreeNode* invertTree(TreeNode* root) {
+        if(root == NULL) return NULL;
+        TreeNode *tmp = root -> left;
+        root -> left = invertTree(root -> right);
+        root -> right = invertTree(tmp);
+        return root;
+    }
+};
+```