leetcode 226翻轉二叉樹(劍指offer.二叉樹的映象)

初級遞迴

1 class Solution:
2     def invertTree(self, root: TreeNode) -> TreeNode:
3         if not root:
4             return 
5         root.left,root.right=root.right,root.left
6         self.invertTree(root.left)
7         self.invertTree(root.right)
8         return
 
 root

一行遞迴

1 class Solution:
2     def invertTree(self, root: TreeNode) -> TreeNode:
3         if not root:
4             return 
5         root.left,root.right=self.invertTree(root.right),self.invertTree(root.left)
6         return root

輔助棧

class Solution:
    def invertTree(self, root: TreeNode) 
 
-> TreeNode:
        if not root:
            return 
        stack=[root]
        while stack:
            node=stack.pop()
            node.left,node.right=node.right,node.left
            if node.left:
                stack.append(node.left)
            if node.right:
                stack.append(node.right)
        
 
return root