很简单的一题，难怪某大牛没写出来被google喷了。。
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.
/**
* 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) {
swap(root);
return root;
}
private void swap (TreeNode root)
{
if(root==null) return ;
TreeNode temp = root.left;
root.left= root.right;
root.right=temp;
swap(root.left);
swap(root.right);
}
}
