二叉树的镜像( 翻转二叉树)

初级递归

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

一行递归

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

辅助栈

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