给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。
示例 1：
输入：root = [4,2,7,1,3,6,9]
输出：[4,7,2,9,6,3,1]
//法一：
class Solution {
public:TreeNode* invertTree(TreeNode* root){if(root == nullptr){return nullptr;}TreeNode* left = invertTree(root->left);TreeNode* right = inverTree(root->right);root->left = right;root->right = left;return root;}
};//法二：
class Solution{
public:TreeNode* invertTree(TreeNode* root){if(root == nullptr){return nullptr;}swap(root->left,root->right);invertTree(root->left);invertTree(root->right);return root;}
};