Invert a binary tree.
二叉树反转
Example:
Input:
4 / \ 2 7 / \ / \ 1 3 6 9
Output:
4 / \ 7 2 / \ / \ 9 6 3 1
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def invertTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
"""
ans = [root]
while ans:
node = ans.pop()
if node:
node.left, node.right = node.right, node.left
ans.extend([node.left, node.right])
return root
"""
if root is None:
return None
root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)
return root