LeetCode -- Invert Binary Tree

Question:

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:



Analysis:

问题描述：给出一个二叉树，然后将它的左右子树置换。

思路：这种题目首先应该反射到递归。用递归有两个条件：return 语句的书写和递归语句的书写。在这道题目中，只要一个节点有任何左节点或者右节点，则应该将他们置换。因此只要非空就置换

。

Answer：

/**
* 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 root;
TreeNode t = root.left;
root.left = root.right;
root.right = t;
invertTree(root.left);
invertTree(root.right);
return root;
}
}