LeetCode 226. Invert Binary Tree （反转二叉树）

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.

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题目标签：Tree

　　这道题目给了我们一个二叉树，让我们把它反转一下。对于每一个点，它的左边和右边子树需要对调一下。利用postOrder 来遍历树，当走到最低端的时候，点 == null， 返回null， 对于每一个点，把它的left 和right 互换一下。return 这个点。

Java Solution:

Runtime beats 27.97% 

完成日期：07/04/2017

关键词：Tree

关键点：把left 和right 互换

/**
 * 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;
        
        // continue children
        invertTree(root.left);
        invertTree(root.right);
        
        // swap left and right
        TreeNode temp;
        temp = root.left;
        root.left = root.right;
        root.right = temp;
        
        return root;
    }
}

参考资料：N/A

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