LeetCode Invert Binary Tree 反转二叉树

# 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
"""
stack=[root]
while stack!=[]:
back=stack.pop()
if back!=None:
back.left, back.right= back.right, back.left
stack.extend([back.left,back.right])#也可以写成stack+=back.left,back.right

return root