text: /**
   * @see {https://leetcode.com/problems/invert-binary-tree/}
   */
  
  /**
   * Definition for a binary tree node.
   * function TreeNode(val, left, right) {
   *     this.val = (val===undefined ? 0 : val)
   *     this.left = (left===undefined ? null : left)
   *     this.right = (right===undefined ? null : right)
   * }
   */
  /**
   * @param {TreeNode} root
   * @return {TreeNode}
   */
  var invertTree = function (root) {
    if (root) {
      const tmp = root.left;
      root.left = root.right;
      root.right = tmp;
  
      invertTree(root.left);
      invertTree(root.right);
    }
  
    return root;
  };