翻转一棵二叉树。

示例：

输入：

     4/   \2     7/ \   / \
1   3 6   9

输出：

     4/   \7     2/ \   / \
9   6 3   1

代码如下:

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     TreeNode *left;*     TreeNode *right;*     TreeNode() : val(0), left(nullptr), right(nullptr) {}*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}* };*/
class Solution {
public:TreeNode* invertTree(TreeNode* root) {if (root==nullptr)return nullptr;TreeNode *leftnode = invertTree(root->left);TreeNode *rightnode = invertTree(root->right);root->left = rightnode;root->right = leftnode;return root;}
};