leetcode：226. Flip binary tree [DFS flip]

analysis

dfs Return the result of this subtree inversion
If it is a leaf node, it will return to itself
If there's a left child , The right child becomes the reverse left child
If there is a right child , The left child becomes the right child after reversal
Then we need to use it. temp Record it in the middle , Can't change sides dfs
temp The initial value is None that will do

ac code

# 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 not root:
            return root
        def dfs(node):
            if node.left is None and node.right is None:
                return node
            
            temp1 = temp2 = None
            
            if node.left:
                temp1 = dfs(node.left)
            if node.right:
                temp2 = dfs(node.right)
            

            node.right = temp1
            node.left = temp2
            
            return node
        
        dfs(root)
        return root

summary

Reverse binary tree used dfs It is also a classic question