数据结构与算法第1章

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Questions and Answers

在优先队列中，元素的优先级是如何排列的？

不进行排序

随机顺序

从高到低 (correct)

从低到高

在Python中，元组中的元素是可以被直接比较的。

False

在使用优先队列时，pop操作返回的是什么？

具有最高优先级的元素

在实现多值字典时，如果希望保留元素的____，应该使用列表。

插入顺序 Signup and view all the answers

将以下数据结构匹配到其描述：

list = 保留插入顺序 set = 消除重复元素 defaultdict = 自动初始化值 tuple = 不可变序列 Signup and view all the answers

在优先队列中，元素是用什么形式存储的？

(priority, index, item) Signup and view all the answers

在Python中，元组的元素可以被修改。

False Signup and view all the answers

创建多值字典的解决方案中，使用哪个模块的哪个类可以方便地实现？

collections模块中的defaultdict类 Signup and view all the answers

在实现优先队列时，使用heapq模块的____函数可以插入元素。

heappush Signup and view all the answers

将以下优先队列中的操作匹配到其功能：

heappush = 插入元素 heappop = 移除最小元素 pop = 得到最高优先级元素 push = 添加一个新元素到队列 Signup and view all the answers

以下哪种方法可以创建一个命名元组？

namedtuple('Name', ['field1', 'field2']) Signup and view all the answers

命名元组的实例是可变的，可以直接修改其属性。

False Signup and view all the answers

如何使用命名元组创建一个包含名称和股份的股票信息？

使用 namedtuple 创建，例如：Stock = namedtuple('Stock', ['name', 'shares']) Signup and view all the answers

命名元组的功能类似于 ________，但占用的内存更少。

字典 Signup and view all the answers

将命名元组的属性与其对应的描述匹配：

addr = 电子邮件地址 joined = 加入日期 name = 股票名称 shares = 持有股份数 Signup and view all the answers

如何替换命名元组中的某个属性值？

s._replace(shares=100) Signup and view all the answers

通过位置来引用命名元组的元素可以提高代码的可读性。

False Signup and view all the answers

命名元组的一个主要用途是什么？

提高代码的可读性和可维护性，减少对元素位置的依赖。 Signup and view all the answers

命名元组与 ________ 不同，后者是可变的。

类 Signup and view all the answers

将命名元组的创建与其用法匹配：

Subscriber = 电子邮件订阅者信息 Stock = 股票信息 Point = 二维坐标点 Record = 数据库记录 Signup and view all the answers

哪些操作可以应用于命名元组？

索引 Signup and view all the answers

命名元组可以作为字典的替代，尤其是在需要更高性能的情况下。

True Signup and view all the answers

什么情况适合使用命名元组而不是字典？

当需要高效地存储固定结构的数据时，且不需要修改。 Signup and view all the answers

在 Python 中，可以将可迭代的对象分解为单独的变量，这种操作称为什么？

元组解包 Signup and view all the answers

如果元组的元素数量与变量数量不匹配，会导致 ValueError 异常。

True Signup and view all the answers

如何使用 Python 的 * 表达式来处理任意长度的可迭代对象？

<ul> <li>表达式可以在序列解包时使用，允许将中间的值放入一个列表中。</li> </ul> Signup and view all the answers

在 Python 中，如果想忽略某些变量，可以使用下划线 (_) 作为变量名，这是一种约定而不是 _____。

语法规则 Signup and view all the answers

将下列操作与其描述相匹配：

x, y = (4, 5) = 将元组的元素分解为两个变量 *middle = grades = 提取中间的成绩 _, shares, price, _ = data = 丢弃某些值 name, email, *phone_numbers = record = 提取姓名、电子邮件和任意数量的电话号码 Signup and view all the answers

在以下代码中，变量 `middle` 将会包含哪些值？ `first, *middle, last = grades`

中间的成绩 Signup and view all the answers

表达式只能在元组的最后一个位置使用。

False Signup and view all the answers

描述 Python 中对可迭代对象使用 * 表达式的两种场景。

一是在处理成绩时丢弃第一个和最后一个成绩，另一是在处理用户记录时提取电话号码。 Signup and view all the answers

在 Python 中，如果想对字符串进行分解，并提取第一个和最后一个值，可以使用 _____ 语法。

<ul> <li>表达式</li> </ul> Signup and view all the answers

下列哪个选项是有效的列表解包示例？

first, *rest, last = [10, 20, 30] Signup and view all the answers

在可迭代对象中，如果只使用单个 *，那么相应的变量将会被忽略。

True Signup and view all the answers

需要将长度超过 N 的可迭代对象解包时，如何处理并获取所需的 N 个值？

使用 * 表达式将多余的值放入一个列表中，可以方便地只提取所需数量的值。 Signup and view all the answers

若要将一列销售额数据的前 7 个季度分解并平均，可使用 _____，而且会确保不需要额外的类型检查。

<ul> <li>表达式</li> </ul> Signup and view all the answers

将下列示例与其功能进行匹配：

data = [ 'ACME', 50, 91.1, (2012, 12, 21) ] = 列表的解包 s = 'Hello' = 字符串的解包 grades = [88, 92, 79, 100] = 成绩的提取 records = [('foo',1,2),('bar','hello')] = 循环解包 Signup and view all the answers

What will be the output of `values['x']` after executing the following code: `values = ChainMap(); values['x'] = 1; values = values.new_child(); values['x'] = 2; values = values.new_child(); values['x'] = 3`?

3 Signup and view all the answers

The `update()` method of a dictionary creates a new dictionary based on the original dictionaries.

False Signup and view all the answers

What data structure allows you to use original dictionaries without creating a new merged dictionary?

ChainMap Signup and view all the answers

Using `ChainMap`, if you modify a variable in the original dictionary, it will __________ in the merged structure.

reflect Signup and view all the answers

Match the following operations with their descriptions:

new_child() = Creates a new mapping with higher precedence parents = Accesses the previous mappings update() = Merges dictionaries into a new one ChainMap() = Combines multiple dictionaries without merging Signup and view all the answers

What is the primary function of the `heapq.heappop()` method?

To remove the lowest priority element from the heap Signup and view all the answers

The priority queue stores elements in the order of their insertion.

False Signup and view all the answers

What structure can be used to create a dictionary that maps keys to multiple values efficiently?

defaultdict Signup and view all the answers

The tuple used in the priority queue is formatted as (_____, index, item).

priority Signup and view all the answers

Match the terms with their descriptions:

heapq.heappush() = Inserts an element into the priority queue heapq.heappop() = Removes the highest priority element defaultdict() = Creates a dictionary with default values tuple() = A fixed-size, immutable sequence Signup and view all the answers

What will happen when trying to compare two Item instances directly?

An error will occur because Item instances are unorderable Signup and view all the answers

The index in the tuple (priority, index, item) can be the same for different elements when their priorities are the same.

False Signup and view all the answers

When creating a multi-value dictionary using defaultdict, what type of container is commonly used?

list or set Signup and view all the answers

The pop operation in a priority queue always returns the element with the ____ priority.

highest Signup and view all the answers

Match each operation with its result:

q.push(Item('foo'), 1) = Adds 'foo' with priority 1 q.pop() = Removes the highest priority item d['a'].append(1) = Adds 1 to the list for key 'a' collections.defaultdict(list) = Creates a defaultdict with list as default container Signup and view all the answers

What is the time complexity to add or pop elements from both ends of a deque?

O(1) Signup and view all the answers

Python's recursion is highly efficient and the preferred method for iterative problems.

False Signup and view all the answers

What module can be used to find the largest or smallest N elements from a collection in Python?

heapq Signup and view all the answers

The operation to append an element to the left side of a deque is called _____

appendleft Signup and view all the answers

Match the following operations with their complexity:

append to deque = O(1) pop from deque = O(1) insert into list head = O(N) append to list = O(1) Signup and view all the answers

In the provided code, the purpose of the 'search' function is to:

Match lines containing a given pattern Signup and view all the answers

A deque can only have a fixed maximum length.

False Signup and view all the answers

What Python keyword is used to create a generator function?

yield Signup and view all the answers

When using heapq.nlargest, the function retrieves the largest elements from a collection based on a _____ function.

key Signup and view all the answers

What is returned by the pop method of the Priority Queue class?

The element with the highest priority Signup and view all the answers

The nlargest() function can only be used with numeric data.

False Signup and view all the answers

What does the term 'priority queue' refer to in data structures?

A queue where elements are processed based on priority rather than order Signup and view all the answers

To create a priority queue, the elements are stored as tuples with the first item being the negative of the priority; this ensures that _____ gets processed first.

highest priority Signup and view all the answers

Match the following heap functions to their purpose:

heapq.nlargest = Finds the largest N elements heapq.nsmallest = Finds the smallest N elements heapq.heapify = Transforms a list into a heap heapq.heappop = Removes and returns the smallest element Signup and view all the answers

What is the primary benefit of using a defaultdict over a regular dictionary when adding values?

It automatically creates empty lists for new keys. Signup and view all the answers

Using setdefault() on a regular dictionary will not create a default entry if the key does not exist.

False Signup and view all the answers

What class in the collections module allows you to maintain the order of elements in a dictionary?

OrderedDict Signup and view all the answers

To find the maximum stock price using a dictionary, you can use the function ___ with a key argument.

max Signup and view all the answers

Match the following operations with their descriptions:

a.keys() & b.keys() = Find keys present in both dictionaries a.keys() - b.keys() = Find keys in a that are not in b a.items() & b.items() = Find (key, value) pairs in common set(a) = Create a set from the list a Signup and view all the answers

What is a common issue when trying to perform calculations directly on dictionary values?

The calculations may return unexpected results. Signup and view all the answers

The items() method of a dictionary allows for set-like operations.

True Signup and view all the answers

What is a generator function used for in the dedupe example?

To remove duplicates and maintain order Signup and view all the answers

When multiple entries have the same value in a dictionary, the ___ is used to determine which entry to return during min or max operations.

key Signup and view all the answers

Match the following dictionary methods with their purpose:

keys() = Returns a view of keys in the dictionary items() = Returns a view of (key, value) pairs values() = Returns a view of values in the dictionary Signup and view all the answers

Which statement about OrderedDict is false?

It has the same memory size as a regular dictionary. Signup and view all the answers

The zip() function can only be used on lists.

False Signup and view all the answers

What is the primary use case for using the dedupe function?

Removing duplicates from a sequence while maintaining order Signup and view all the answers

To create a dictionary that eliminates certain keys, one can use a dictionary comprehension along with the ___ method.

keys() Signup and view all the answers

Which of the following is NOT a built-in data structure in Python?

Array Signup and view all the answers

You can unpack a sequence directly into a different number of variables without any issues.

False Signup and view all the answers

What does the '*' expression do in Python?

It allows unpacking of elements from an iterable and can capture excess values into a list. Signup and view all the answers

To discard specific values during unpacking in Python, you can use a variable name like ______.

_ Signup and view all the answers

Match the following Python operations with their purposes:

x, y = p = Unpacking a tuple into two variables *middle = grades = Capturing excess elements into a list _, shares, price, _ = data = Ignoring specific elements during unpacking def drop_first_last(grades) = Dropping the first and last items from a list Signup and view all the answers

What will happen if the number of elements does not match the number of variables during unpacking?

A ValueError will occur. Signup and view all the answers

The args variable in a function definition behaves similarly to the expression in unpacking.

True Signup and view all the answers

Provide an example of a valid use of the * expression when unpacking.

first, *middle, last = grades Signup and view all the answers

The variable name used to indicate ignored values during unpacking can be represented as ______.

ign Signup and view all the answers

Match the following error types with their descriptions:

ValueError = Occurs when the number of variables does not match the number of elements to unpack IndexError = Occurs when attempting to access an index that is out of range TypeError = Occurs when an operation is applied to an object of inappropriate type KeyError = Occurs when a dictionary key is not found Signup and view all the answers

In which scenario would you typically use the * expression?

When unpacking a variable number of elements into distinct variables Signup and view all the answers

Using list unpacking, it is possible to retain the structure of the original list.

False Signup and view all the answers

What will the variable phone_numbers contain if you unpack a record of a user as: (name, email, *phone_numbers)?

A list of phone numbers Signup and view all the answers

In Python, to refer to the first element of a list and the remaining as the tail, you can use the syntax ______.

head, *tail = items Signup and view all the answers

How can you safely ignore certain values while unpacking?

Using '_' Signup and view all the answers

Study Notes

数据结构和算法

Python 内置了常用的数据结构，如列表（list）、集合（set）和字典（dictionary），大部分情况下可直接使用。
本章讨论常见数据结构及相关算法，适用于搜索、排序、筛选等问题。
collections 模块提供了多种数据结构的解决方案。

序列分解

可将元组或序列分解为单独变量，要求变量数量与序列结构一致。
Python支持对可迭代对象进行分解，适用范围包括字符串、文件、迭代器等。
当分解时可用“_”忽略不需的变量，确保选用的变量名未被重复使用。

任意长度可迭代对象分解

使用“*表达式”可从可迭代对象分解出元素，适用于长度超过N的情况。
示例：课程成绩中去掉第一个和最后一个，使用*middle机制可轻松实现。
遇到可变长度的数据集合时，*表达式有效帮助分解。

筛选序列中的元素

列表推导式（list comprehension）是筛选序列数据的简单方法。
在处理大数据时，生成器表达式为更高效的选择，使内存使用更加优化。
复杂筛选条件可使用内置的filter()函数，通过单独函数处理筛选逻辑。

从字典中提取子集

字典推导式（dictionary comprehension）便能轻松创建字典的子集，效率高且代码清晰。
使用元组序列转为字典的方式次之，性能较低，但用于简单场景依旧有效。

映射与字典

collections.namedtuple()可创建命名元组，提供以名称访问元素的能力，增强代码可读性。
namedtuple 不可变，适合构建高效、结构化的数据，但不适用于需要频繁修改的场景。
使用 replace() 方法可替换命名元组中的某些字段，方便处理缺失值。

数据转换与汇总

可以在函数参数中使用生成器表达式来同时做数据转化和汇总操作，如计算平方和。
某些汇总函数（如min()、max()）可使用key参数提升灵活性。

合并多个映射

使用 collections 的 ChainMap 类，能逻辑上将多个字典并入一个池，简化查找过程。
ChainMap不实际合并字典，维持原字典结构，常用在键重叠时优先使用第一个字典的值。

数据结构和算法概述

Python 内置列表（list）、集合（set）和字典（dictionary）等有用的数据结构，适合大多数情况。
需要解决常见问题如搜索、排序、排列和筛选，建议使用 collections 模块中的解决方案。

将序列分解为单独的变量

可通过简单的赋值将元组或序列分解为变量，变量数量与序列数量必须匹配。
支持分解的可迭代对象包括字符串、文件、迭代器和生成器。
使用一个变量名（如下划线 _）可丢弃某些值，不需特殊语法。

从任意长度的可迭代对象分解元素

使用“*表达式”可以从可迭代对象中提取长度不固定的元素。
允许从任意长度的可迭代对象中提取所需的部分而不报错。
使用示例包括提取课程成绩或用户信息中的电话号码。

保存最后 N 个元素

使用 collections.deque 保存历史记录，自动移除最旧的记录。
deque 提供高效的 O(1) 操作，适合简单队列结构。

找到最大或最小的 N 个元素

使用 heapq 模块的 nlargest() 和 nsmallest() 函数找出集合中最大或最小的 N 个元素。
这两个函数可以接收 key 参数，支持更复杂的数据结构处理。

实现优先级队列

自定义 PriorityQueue 类利用 heapq 模块实现优先级队列。
每次弹出操作返回优先级最高的元素，以元组 (-priority, index, item) 的形式进行排序。

在字典中将键映射到多个值

利用列表或集合存储字典中一个键对应多个值。
使用 collections.defaultdict 方便创建一键多值字典，避免手动初始化。

让字典保持有序

使用 collections.OrderedDict 控制字典元素的顺序，确保迭代时按照添加顺序。
OrderedDict 在序列化（如 JSON 编码）时也能保持顺序。

与字典有关的计算问题

使用 zip() 将字典的键和值反转，可以计算最小值、最大值，或对字典内容进行排序。
注意 zip() 创建的迭代器只能消费一次，避免重复使用出错。

在两个字典中寻找相同点

通过 keys() 或 items() 方法在字典间进行集合操作，找出相同键和值。
可使用字典推导式过滤字典内容，创建新的字典。

从序列中移除重复项且保持元素间顺序不变

通过集合和生成器解决去重问题，同时保持顺序。
可处理不可哈希的对象，通过 key 参数指定转换函数以实现去重。

ChainMap 与字典合并

ChainMap 允许多个字典的上下文合并，保留原始字典的数据。
使用 dict.update() 方法合并字典时，将创建新字典，不保留原始字典的变更。

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Description

本章将深入探讨Python内置的数据结构，包括列表、集合和字典。我们还将讨论如何解决搜索和排序等常见问题，以及在collections模块中的解决方案。适合对数据处理感兴趣的学习者。

数据结构与算法 第1章

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Questions and Answers

在优先队列中，元素的优先级是如何排列的？

在Python中，元组中的元素是可以被直接比较的。

在使用优先队列时，pop操作返回的是什么？

在实现多值字典时，如果希望保留元素的____，应该使用列表。

将以下数据结构匹配到其描述：

在优先队列中，元素是用什么形式存储的？

在Python中，元组的元素可以被修改。

创建多值字典的解决方案中，使用哪个模块的哪个类可以方便地实现？

在实现优先队列时，使用heapq模块的____函数可以插入元素。

将以下优先队列中的操作匹配到其功能：

以下哪种方法可以创建一个命名元组？

命名元组的实例是可变的，可以直接修改其属性。

如何使用命名元组创建一个包含名称和股份的股票信息？

命名元组的功能类似于 ________，但占用的内存更少。

将命名元组的属性与其对应的描述匹配：

如何替换命名元组中的某个属性值？

通过位置来引用命名元组的元素可以提高代码的可读性。

命名元组的一个主要用途是什么？

命名元组与 ________ 不同，后者是可变的。

将命名元组的创建与其用法匹配：

哪些操作可以应用于命名元组？

命名元组可以作为字典的替代，尤其是在需要更高性能的情况下。

什么情况适合使用命名元组而不是字典？

在 Python 中，可以将可迭代的对象分解为单独的变量，这种操作称为什么？

如果元组的元素数量与变量数量不匹配，会导致 ValueError 异常。

如何使用 Python 的 * 表达式来处理任意长度的可迭代对象？

在 Python 中，如果想忽略某些变量，可以使用下划线 (_) 作为变量名，这是一种约定而不是 _____。

将下列操作与其描述相匹配：

在以下代码中，变量 middle 将会包含哪些值？ first, *middle, last = grades

表达式只能在元组的最后一个位置使用。

描述 Python 中对可迭代对象使用 * 表达式的两种场景。

在 Python 中，如果想对字符串进行分解，并提取第一个和最后一个值，可以使用 _____ 语法。

下列哪个选项是有效的列表解包示例？

在可迭代对象中，如果只使用单个 *，那么相应的变量将会被忽略。

需要将长度超过 N 的可迭代对象解包时，如何处理并获取所需的 N 个值？

若要将一列销售额数据的前 7 个季度分解并平均，可使用 _____，而且会确保不需要额外的类型检查。

将下列示例与其功能进行匹配：

What will be the output of values['x'] after executing the following code: values = ChainMap(); values['x'] = 1; values = values.new_child(); values['x'] = 2; values = values.new_child(); values['x'] = 3?

The update() method of a dictionary creates a new dictionary based on the original dictionaries.

What data structure allows you to use original dictionaries without creating a new merged dictionary?

Using ChainMap, if you modify a variable in the original dictionary, it will __________ in the merged structure.

Match the following operations with their descriptions:

What is the primary function of the heapq.heappop() method?

The priority queue stores elements in the order of their insertion.

What structure can be used to create a dictionary that maps keys to multiple values efficiently?

The tuple used in the priority queue is formatted as (_____, index, item).

Match the terms with their descriptions:

What will happen when trying to compare two Item instances directly?

The index in the tuple (priority, index, item) can be the same for different elements when their priorities are the same.

When creating a multi-value dictionary using defaultdict, what type of container is commonly used?

The pop operation in a priority queue always returns the element with the ____ priority.

Match each operation with its result:

What is the time complexity to add or pop elements from both ends of a deque?

Python's recursion is highly efficient and the preferred method for iterative problems.

What module can be used to find the largest or smallest N elements from a collection in Python?

The operation to append an element to the left side of a deque is called _____

Match the following operations with their complexity:

In the provided code, the purpose of the 'search' function is to:

A deque can only have a fixed maximum length.

What Python keyword is used to create a generator function?

When using heapq.nlargest, the function retrieves the largest elements from a collection based on a _____ function.

What is returned by the pop method of the Priority Queue class?

The nlargest() function can only be used with numeric data.

What does the term 'priority queue' refer to in data structures?

To create a priority queue, the elements are stored as tuples with the first item being the negative of the priority; this ensures that _____ gets processed first.

Match the following heap functions to their purpose:

What is the primary benefit of using a defaultdict over a regular dictionary when adding values?

Using setdefault() on a regular dictionary will not create a default entry if the key does not exist.

What class in the collections module allows you to maintain the order of elements in a dictionary?

To find the maximum stock price using a dictionary, you can use the function ___ with a key argument.

Match the following operations with their descriptions:

What is a common issue when trying to perform calculations directly on dictionary values?

The items() method of a dictionary allows for set-like operations.

What is a generator function used for in the dedupe example?

When multiple entries have the same value in a dictionary, the ___ is used to determine which entry to return during min or max operations.

Match the following dictionary methods with their purpose:

数据结构与算法第1章

在以下代码中，变量 `middle` 将会包含哪些值？ `first, *middle, last = grades`

What will be the output of `values['x']` after executing the following code: `values = ChainMap(); values['x'] = 1; values = values.new_child(); values['x'] = 2; values = values.new_child(); values['x'] = 3`?

The `update()` method of a dictionary creates a new dictionary based on the original dictionaries.

Using `ChainMap`, if you modify a variable in the original dictionary, it will __________ in the merged structure.

What is the primary function of the `heapq.heappop()` method?

The args variable in a function definition behaves similarly to the expression in unpacking.