leetcode_c++:树:Invert Binary Tree（226 )

Invert a binary tree.

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

to

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

---

class Solution {public:    TreeNode* invertTree(TreeNode* root) {        if (root) {            swap(root->left, root->right);            invertTree(root->left);            invertTree(root->right);        }        return root;    }};