LeetCode-剑指 Offer 27. 二叉树的镜像
请完成一个函数,输入一个二叉树,该函数输出它的镜像。
示例 1:
输入:root = [4,2,7,1,3,6,9]
输出:[4,7,2,9,6,3,1]
Python 利用平行赋值的写法(即 a, b = b, aa,b=b,a ),可省略暂存操作。其原理是先将等号右侧打包成元组 (b,a)(b,a) ,再序列地分给等号左侧的 a, ba,b 序列。
思路1:
用递归处理,自下而上处理
class Solution:
def mirrorTree(self, root: TreeNode) -> TreeNode:
if not root: return
root.left, root.right = self.mirrorTree(root.right), self.mirrorTree(root.left)
return root
思路2:
用栈来存储结点,自上而下处理
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def mirrorTree(self, root: TreeNode) -> TreeNode:
if not root: return
stack = [root]
while stack:
node = stack.pop()
if node.left: stack.append(node.left)
if node.right: stack.append(node.right)
node.left, node.right = node.right, node.left
return root