Invert a binary tree.
Example:
Input:
4
/ \
2 7
/ \ / \
1 3 6 9
Output:
4
/ \
7 2
/ \ / \
9 6 3 1
Solution
这个题，我们假设某个节点的左右子树已经invert了，那么对于该节点我们只需要简单交换一下它的左右子树。如果节点为空。则退出递归。
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution:
def invertTree(self, root: TreeNode) -> TreeNode:
if root is None:
return None
root.left,root.right = self.invertTree(root.right),self.invertTree(root.left)
return root
