Leetcode226. 翻转二叉树

翻转一棵二叉树。

示例：

输入：

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

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

思路

左右递归替换，每个节点运行一遍，O(n)。

# 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 == None:return None
        right = self.invertTree(root.right)
        left = self.invertTree(root.left)
        root.left  = right
        root.right = left
        return root