25期代码随想录算法训练营第十四天 | 二叉树 | 递归遍历、迭代遍历

目录

递归遍历

前序遍历

python 复制代码
# 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 preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        left = self.preorderTraversal(root.left)
        right = self.preorderTraversal(root.right)

        return [root.val] + left + right

中序遍历

python 复制代码
# 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 inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        left = self.inorderTraversal(root.left)
        right = self.inorderTraversal(root.right)

        return left + [root.val] + right

后序遍历

python 复制代码
# 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 postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        left = self.postorderTraversal(root.left)
        right = self.postorderTraversal(root.right)

        return left + right + [root.val]

迭代遍历

前序遍历

python 复制代码
# 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 preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        stack = [root]
        res = []

        while stack:
            cur = stack.pop()
            res.append(cur.val)  # 在这里加入节点值

            # 先右后左地加入子节点到栈中
            if cur.right:
                stack.append(cur.right)
            if cur.left:
                stack.append(cur.left)

        return res

中序遍历

为什么这样能实现左中右的逻辑?

为什么需要使用while cur or stack?

python 复制代码
# 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 inorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        stack = []
        res = []
        cur = root

        while cur or stack:
            if cur:
                stack.append(cur)
                cur = cur.left
            else:
                cur = stack.pop()
                res.append(cur.val)
                cur = cur.right

        return res

后序遍历

中右左 ---->再颠倒顺序成为 左右中

python 复制代码
# 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 postorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
        if not root:
            return []

        res = []
        stack = [root]

        while stack:
            node = stack.pop()
            res.append(node.val)

            if node.left:
                stack.append(node.left)
            if node.right:
                stack.append(node.right)
        
        return res[::-1]
相关推荐
lljss202021 分钟前
Python11中创建虚拟环境、安装 TensorFlow
开发语言·python·tensorflow
课堂剪切板22 分钟前
ch03 部分题目思路
算法
空中湖23 分钟前
tensorflow武林志第二卷第九章:玄功九转
人工智能·python·tensorflow
山登绝顶我为峰 3(^v^)31 小时前
如何录制带备注的演示文稿(LaTex Beamer + Pympress)
c++·线性代数·算法·计算机·密码学·音视频·latex
CodeCraft Studio1 小时前
CAD文件处理控件Aspose.CAD教程:使用 Python 将绘图转换为 Photoshop
python·photoshop·cad·aspose·aspose.cad
Two_brushes.2 小时前
【算法】宽度优先遍历BFS
算法·leetcode·哈希算法·宽度优先
Python×CATIA工业智造3 小时前
Frida RPC高级应用:动态模拟执行Android so文件实战指南
开发语言·python·pycharm
onceco4 小时前
领域LLM九讲——第5讲 为什么选择OpenManus而不是QwenAgent(附LLM免费api邀请码)
人工智能·python·深度学习·语言模型·自然语言处理·自动化
森焱森4 小时前
水下航行器外形分类详解
c语言·单片机·算法·架构·无人机
狐凄4 小时前
Python实例题:基于 Python 的简单聊天机器人
开发语言·python