Java for LeetCode 226 Invert Binary Tree

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:

解题思路：

递归即可，JAVA实现如下：

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