From 54bcab13e37ee1e609b567411b968bdb5a86abac Mon Sep 17 00:00:00 2001 From: jianghongcheng <35664721+jianghongcheng@users.noreply.github.com> Date: Wed, 3 May 2023 20:25:30 -0500 Subject: [PATCH] =?UTF-8?q?Update=200226.=E7=BF=BB=E8=BD=AC=E4=BA=8C?= =?UTF-8?q?=E5=8F=89=E6=A0=91.md?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- problems/0226.翻转二叉树.md | 163 +++++++++++++++++++++++-------- 1 file changed, 120 insertions(+), 43 deletions(-) diff --git a/problems/0226.翻转二叉树.md b/problems/0226.翻转二叉树.md index 16a5be57..63baa409 100644 --- a/problems/0226.翻转二叉树.md +++ b/problems/0226.翻转二叉树.md @@ -314,81 +314,158 @@ class Solution { 递归法:前序遍历: ```python +# 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 None - root.left, root.right = root.right, root.left #中 - self.invertTree(root.left) #左 - self.invertTree(root.right) #右 + root.left, root.right = root.right, root.left + self.invertTree(root.left) + self.invertTree(root.right) return root ``` -递归法:后序遍历: +迭代法:前序遍历: ```python +# 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: + if not root: + return None + 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 +``` + + +递归法:中序遍历: +```python +# 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 None + self.invertTree(root.left) + root.left, root.right = root.right, root.left + self.invertTree(root.left) + return root +``` + +迭代法:中序遍历: +```python +# 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 None + stack = [root] + while stack: + node = stack.pop() + if node.left: + stack.append(node.left) + node.left, node.right = node.right, node.left + if node.left: + stack.append(node.left) + return root +``` + + +递归法:后序遍历: +```python +# 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 None self.invertTree(root.left) self.invertTree(root.right) root.left, root.right = root.right, root.left - return root + return root ``` -迭代法:深度优先遍历(前序遍历): +迭代法:后序遍历: ```python +# 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 - st = [] - st.append(root) - while st: - node = st.pop() - node.left, node.right = node.right, node.left #中 - if node.right: - st.append(node.right) #右 + return None + stack = [root] + while stack: + node = stack.pop() if node.left: - st.append(node.left) #左 + stack.append(node.left) + if node.right: + stack.append(node.right) + node.left, node.right = node.right, node.left + return root ``` + + + + 迭代法:广度优先遍历(层序遍历): ```python -import collections +# 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: - queue = collections.deque() #使用deque() - if root: - queue.append(root) + if not root: + return None + + queue = collections.deque([root]) while queue: - size = len(queue) - for i in range(size): + for i in range(len(queue)): node = queue.popleft() - node.left, node.right = node.right, node.left #节点处理 - if node.left: - queue.append(node.left) - if node.right: - queue.append(node.right) - return root -``` -迭代法:广度优先遍历(层序遍历),和之前的层序遍历写法一致: -```python -class Solution: - def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]: - if not root: return root - from collections import deque - que=deque([root]) - while que: - size=len(que) - for i in range(size): - cur=que.popleft() - cur.left, cur.right = cur.right, cur.left - if cur.left: que.append(cur.left) - if cur.right: que.append(cur.right) + node.left, node.right = node.right, node.left + if node.left: queue.append(node.left) + if node.right: queue.append(node.right) return root + ``` + ### Go 递归版本的前序遍历