Description：

Invert a binary tree.

  

      4

    /    \

  2      7

 /  \    /   \

1   3   6   9

to

4   /   \  7     2 / \   / \9   6 3   1 递归invert就好了。

/** * 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;        invert(root);        return root;                }    public static void invert(TreeNode root) {        if(root==null || (root.right == null && root.left==null)) {            return;        }        TreeNode rNode = root.right;        TreeNode lNode = root.left;        root.right = lNode;        root.left = rNode;        invert(root.left);        invert(root.right);    }}