翻转二叉树

 1 /**
 2  * Definition for a binary tree node.
 3  * function TreeNode(val, left, right) {
 4  *     this.val = (val===undefined ? 0 : val)
 5  *     this.left = (left===undefined ? null : left)
 6  *     this.right = (right===undefined ? null : right)
 7  * }
 8  */
 9 /**
10  * @param {TreeNode} root
11  * @return {TreeNode}
12  */
13 var invertTree = function(root) {
14     //判断当前树是否为 null
15     if(root == null) return root;
16     //左右子树结点交换
17     let right = root.right;
18     let left = root.left;
19     root.right = left;
20     root.left = right;
21     //分别对左右子树进行递归
22     invertTree(left);
23     invertTree(right);
24     //返回树的根节点
25     return root;
26 };