# 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

        """

        if root is None:

            return None

        if root.left:

            self.invertTree(root.left)

        if root.right:

            self.invertTree(root.right)

        root.left,root.right=root.right,root.left

        return root