理论与实践

数据输入输出

任务

条件语句

任务

for循环

任务

字符串

任务

while循环

任务

列表

任务

二维数组

任务

字典

任务

集合

任务

函数与递归

任务

课程 9. Sets

难度：

任务«基础分析»

💻 Python

健身中心希望分析其客户群体，以便识别符合特定条件的客户，从而进行精准广告投放。您拥有以一组特征形式呈现的客户数据。需要开发一个程序，能够同时找出满足多个指定条件的客户。

输入格式

第一行输入数字 n ——客户总数。
接下来，对于每个客户（共 n 行），按以下格式输入其信息： id age gender subscription interest_1 interest_2 ... interests 。
id ——唯一客户标识符（整数）。
age ——客户年龄（整数）。
gender ——客户性别（'m' 表示男性，'f' 表示女性）。
subscription ——是否有订阅（'y' 表示是，'n' 表示否）。
interest_1 interest_2 ... interests ——客户兴趣列表（由空格分隔的字符串）。每个客户的兴趣数量可以不同。

在客户数据输入完毕后，输入数字 m ——搜索条件的数量。
接下来，对于每个条件（共 m 行），按格式 type value 输入条件。其中： type ——条件类型（可选值： age 、 gender 、 subscription 、 interest ）。
value ——条件的值。对于类型 age 为整数，对于类型 gender 为 'm' 或 'f'，对于类型 subscription 为 'y' 或 'n'，对于类型 interest 为字符串。

输出格式

显示满足所有指定条件的客户标识符列表，按排序方式以空格分隔。如果没有客户符合条件，则显示 "none"

示例

输入

5
1 25 m Y 游泳健身
2 30 f n 瑜伽普拉提
3 25 f Y 舞蹈瑜伽
4 40 m y 健身拳击
5 30 m n 游泳拳击 3
年龄 25
性别 f
兴趣瑜伽

输出

提示

Comparing sets

Subset

A set A is a subset of set B if all elements of set A, without exception, are also contained in set B. The issubset() method is used to check this condition. and the operator .

A useful tip: The <= operator checks for a "non-strict" subset. This means that any set is a subset of itself (set1<= set1 returns True). If you need to check that the set A is a subset of B, but it is not equal to it, use the strict inequality operator .

set1 = {1, 2}
set2 = {1, 2, 3}
set3 = {1, 2}

# Checking for a subset
print(set1.issubset(set2))  # Output: True
print(set1 <= set2) # Output: True

# Checking for a strict subset
print(set1 < set2) # Output: True
print(set3< set1) # Output: False, since the sets are equal

Superset

A set A is a superset of set B if it contains all the elements that are in set B. The issuperset() method is used for verification. and the operator =.

A useful tip: Similarly to subsets, the = operator checks for a "non-strict" superset. To check for a strict superset (A contains all the elements of B and at least one additional one), use the operator.

set1 = {1, 2, 3}
set2 = {1, 2}

# Checking for a superset
print(set1.issuperset(set2))  # Output: True
print(set1 >= set2) # Output: True

# Checking for a strict superset
print(set1 > set2) # Output: True
print(set1 > {1, 2, 3}) # Conclusion: False, since the sets are equal

Equality of sets

Sets are considered equal if they contain exactly the same set of elements. The order of the elements does not matter at all. The == operator is used for verification.

set1 = {1, 2, 3}
set2 = {3, 2, 1}
set3 = {1, 2, 3, 3} # The duplicate will be ignored when creating a set.

print(set1 == set2) # Output: True
print(set1 == set3) # Output: True

Other set methods

Copying a set

The copy() method returns a surface copy of the set.

Important advice: Do not confuse copying with assignment. If you write set2 = set1, then set2 will not be a new set, but only another reference to set1. Changing set2 will change set1. Use copy() to create an independent array.

set1 = {1, 2, 3}

# Correct copying
set2 = set1.copy()
set2.add(4)
print(f"Original set1: {set1}")  # Output: Original set1: {1, 2, 3}
print(f"Copy of set2: {set2}")    # Output: A copy of set2: {1, 2, 3, 4}

# Incorrect copying (link assignment)
set3 = set1
set3.add(5)
print(f"Original set1 after changing set3: {set1}") # Output: Original set1 after changing set3: {1, 2, 3, 5}
print(f"Reference set3: {set3}")                       # Output: set3 link: {1, 2, 3, 5}

Updating the set

The update() method adds to the current set all the elements from another set or any other iterable object (for example, a list or a tuple). The method modifies the original set and returns nothing (None).

set1 = {1, 2, 3}
set2 = {3, 4, 5}
list1 = [5, 6, 7]

set1.update(set2) # Duplicate {3} will be ignored
print(set1) # Output: {1, 2, 3, 4, 5}

set1.update(list1) # You can update it from the list
print(set1) # Output: {1, 2, 3, 4, 5, 6, 7}

Sets and their applications

Arrays are extremely useful in various tasks due to their speed and unique properties. They are ideal for removing duplicates, quickly checking for an element, and performing mathematical operations (union, intersection, difference).

Removing duplicates from the list

This is one of the most common uses of arrays. Converting a list to a set automatically removes all duplicates. Then, if necessary, the set can be converted back to a list.

It is important to remember: With this transformation, the original order of the list items is not preserved.

numbers = [1, 2, 2, 3, 4, 4, 5, 1]
unique_numbers = list(set(numbers))
print(unique_numbers) # The output can be [1, 2, 3, 4, 5] ( the order is not guaranteed)

Search for common items in two lists

To find the elements that are present in both collections, you can transform them into sets and use the intersection operator &.

list1 = [1, 2, 3, 4]
list2 = [3, 4, 5, 6]
common_elements = list(set(list1) & set(list2))
print(common_elements)  # Output: [3, 4] (order is not guaranteed)

Search for unique elements (symmetric difference)

To find the elements that are in one of the lists, but not both at once, use the symmetric difference operator ^.

list1 = [1, 2, 3, 4]
list2 = [3, 4, 5, 6]
unique_to_each_list = list(set(list1) ^ set(list2))
print(unique_to_each_list) # Output: [1, 2, 5, 6] ( the order is not guaranteed)