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Lektion 9. Sets
Schwierigkeit:
Aufgabe«Die Buchwelt»
💻 Python
Im Online-Shop "Buchwelt" wurde beschlossen, die Vorlieben ihrer Kunden zu analysieren. Sie haben Daten über zwei Kundengruppen: diejenigen, die Bücher im Genre Fantastik gekauft haben, und diejenigen, die Bücher im Genre Detektiv gekauft haben. Es ist notwendig zu ermitteln, welche Kunden Bücher nur in einem dieser Genres gekauft haben (entweder nur Science-Fiction oder nur einen Detektivroman).
Eingabeformat
Zuerst die Zahl & nbsp; n & nbsp; & ndash; Die Anzahl der Käufer, die Bücher im Genre Fantasie gekauft haben. Dann & nbsp; n & nbsp; Zeilen mit den Namen dieser Käufer.
Danach die Zahl & nbsp; m & nbsp; & ndash; Die Anzahl der Käufer, die Bücher im Genre Detektiv gekauft haben. Dann & nbsp; m Zeilen mit den Namen dieser Käufer.
Danach die Zahl & nbsp;
Ausgabeformat
Geben Sie die Namen der Käufer aus, die Bücher in nur einem der Genres gekauft haben (entweder nur "Science-Fiction" oder nur "Krimi"). Die Namen sollen in alphabetischer Reihenfolge sortiert und jeder Name in einer separaten Zeile angezeigt werden.
Beispiel
Eingabe
3
Ivanov
Petrov
Sidorov
2
Petrov
Smirnov
Ausgabe
Iwanow
Smirnow
Sidorow
Hinweis
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)
main.py
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
Test 8
Test 9
Test 10
Entwicklerlösung
