leetcode -. 226 Flip binary tree

In fact, it is not clear to do so in the end can not, then it becomes. .

Ideas like or thorough enough, there is a vague point, and did not fully grasp.

Although it is doing the right thing, but not necessarily the next time, or if then a little more complicated, but probably not. . . .

class Solution:
    def invertTree(self, root: TreeNode) -> TreeNode:
        if not root:
            return root
        def helper(node):
            if node:
                if node.left or node.right:
                    node.left,node.right=node.right,node.left
                helper(node.left)
                helper(node.right)
        helper(root)
        return root

When execution: 48 ms, beat the 47.66% of users in all python3 submission

Memory consumption: 13.9 MB, beat the 5.24% of users in all python3 submission

 

——2019.11.19