学习笔记_数据结构：Python 构建/遍历树

最新推荐文章于 2022-12-18 17:30:15 发布

原创最新推荐文章于 2022-12-18 17:30:15 发布 · 228 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#python

Python 专栏收录该内容

13 篇文章

订阅专栏

这篇学习笔记介绍了如何用列表构建二叉树，并实现了层次遍历、先序遍历、中序遍历和后序遍历的方法。通过一个具体的例子展示了这些遍历过程及其输出结果。

学习笔记_数据结构_树_(1)

时间：2021年7月14日
作者：Afollower
分类：学习记录/数据结构/树

通过列表构建二叉树，并实现二叉树层次遍历，先序遍历，中序遍历和后序遍历

# -*- coding: UTF-8 -*-
from collections import deque


class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Tree:
    def __init__(self, tree: list):
        self.tree = tree
        self.root = TreeNode(None)
        self.create_tree()

    def create_tree(self):
        """
        构建树
        """
        if not self.tree:
            return None
        self.root = TreeNode(self.tree[0])
        queue = deque([self.root])
        len_tree = len(self.tree)
        nums = 1
        while nums < len_tree:
            node = queue.popleft()
            if node:
                node.left = TreeNode(self.tree[nums]) if self.tree[nums] else None
                queue.append(node.left)
                if nums + 1 < len_tree:
                    node.right = TreeNode(self.tree[nums + 1]) if self.tree[nums + 1] else None
                    queue.append(node.right)
                    nums += 1
                nums += 1

    def get_tree_by_bfs(self):
        """
        层次遍历
        :return:list
        """
        res = []
        queue = deque([self.root])
        while queue:
            node = queue.popleft()
            if node:
                res.append(node.val)
                queue.append(node.left)
                queue.append(node.right)
        return res

    def pre_traversal(self):
        """
        先序遍历
        """
        res = []

        def traversal(head: TreeNode):
            if not head:
                return
            res.append(head.val)
            traversal(head.left)
            traversal(head.right)

        traversal(self.root)
        return res

    def in_traversal(self):
        """
        中序遍历
        """
        res = []

        def traversal(head: TreeNode):
            if not head:
                return
            traversal(head.left)
            res.append(head.val)
            traversal(head.right)
        traversal(self.root)
        return res

    def post_traversal(self):
        """
        后序遍历
        """
        res = []

        def traversal(head: TreeNode):
            if not head:
                return
            traversal(head.left)
            traversal(head.right)
            res.append(head.val)
        traversal(self.root)
        return res


tree = Tree([3, 9, 20, 15, 7, None, None])
print(tree.get_tree_by_bfs())
print(tree.pre_traversal())
print(tree.in_traversal())
print(tree.post_traversal())

输出

[3, 9, 20, 15, 7]
[3, 9, 15, 7, 20]
[15, 9, 7, 3, 20]
[15, 7, 9, 20, 3]