226.cpp

// recursion-3ms.cpp
/**
 * 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 == NULL)
      return NULL;
    TreeNode *left = root->left, *right = root->right;
    root->left = right;
    root->right = left;
    invertTree(root->left);
    invertTree(root->right);
    return root;
  }
};