leetcode-Invert Binary Tree

Invert a binary tree.

     4
   /   \
  2     7
 / \   / \
1   3 6   9

to

     4
   /   \
  7     2
 / \   / \
9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

296ms，不过我觉得还是想试试其他的，比如说用stack，把2叉树先序存起来，然后倒序遍历二叉树的方式读出来，然而并没有什因为定义树的一种自然方式就是递归

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution { public TreeNode invertTree(TreeNode root) { if(root==null) return null; if(root.left==null && root.right == null) return root; TreeNode lNode = root.left; TreeNode rNode = root.right; root.right = lNode; invertTree(root.right); root.left = rNode; invertTree(root.left); return root; } }