226. 翻转二叉树（算法200题-7）

/**
 * 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 === null) {
    return root
  }
    // 递归 反转节点
  [root.left, root.right] = [invertTree(root.right), invertTree(root.left)]
  return root
};