text: /**
   * Definition for a binary tree node.
   * struct TreeNode {
   *     int val;
   *     TreeNode *left;
   *     TreeNode *right;
   *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
   *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
   *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
   * };
   */
  class Solution {
  public:
      TreeNode* invertTree(TreeNode* root) {
          if (!root) return root;
  	    TreeNode* temp = invertTree(root->left);
  	    root->left = invertTree(root->right);
  	    root->right = temp;
  	    return root;
      }
  };
  