[easy][Tree]226.Invert Binary Tree

原题是：

Screen Shot 2017-11-05 at 3.17.19 PM.png

代码是：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def invertTree(self, root):
        """
        :type root: TreeNode
        :rtype: TreeNode
        """
        tmp = TreeNode(0)
        if root == None:
            return root
        else :
            tmp = root.left
            root.left = root.right
            root.right = tmp
            self.invertTree(root.right)
            self.invertTree(root.left)
            
        return root