如果当前遍历到的节点 \textit{root}root 的左右两棵子树都已经翻转,那么我们只需要交换两棵子树的位置,即可完成以 \textit{root}root 为根节点的整棵子树的翻转。
/**
* 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) return root;
TreeNode *left = invertTree(root->left);
TreeNode *right = invertTree(root->right);
root->left = right;
root->right = left;
return root;
}
};