Invert Binary Tree

https://leetcode.com/problems/invert-binary-tree/

Invert a binary tree.

     4
   /   \
  2     7
 / \   / \
1   3 6   9

to

     4
   /   \
  7     2
 / \   / \
9   6 3   1


直接用递归

# 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:
            root.left,root.right = root.right,root.left
            self.invertTree(root.left)
            self.invertTree(root.right)
        return root