leetcode_226

题目来源：https://leetcode.com/problems/invert-binary-tree/

审题：也就是左右子树交换，采用递归法

代码：
/**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }
• }
  */
  class Solution {
  public TreeNode invertTree(TreeNode root) {

  if(root == null){
      return null;
  }
  TreeNode right = invertTree(root.right);
  TreeNode left = invertTree(root.left);
  root.left = right;
  root.right = left;
  return root;
  

  }
  }