leetcode 226. Invert Binary Tree

Invert a binary tree.
4
/ \
2 7
/ \ / \
1 3 6 9
to
4
/ \
7 2
/ \ / \
9 6 3 1

镜像翻转 左子树和右子树交换，利用递归完成

/** * 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* invertTree(TreeNode* root)     {        if(root == nullptr)            return root;        if(root->left != nullptr|| root->right != nullptr)        {             TreeNode*temp ;             temp = root ->left;            root->left =  root ->right;            root->right = temp;            invertTree(root->left);            invertTree(root->right);        }         return root;     }};