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Lektion 9. Sets
Schwierigkeit:
Aufgabe«Unterschied der Interessen»
💻 Python
In der Online-Community der Brettspielliebhaber wird eine Umfrage durchgeführt, um herauszufinden, welche Spiele am beliebtesten sind. Jeder Teilnehmer gibt eine Liste seiner Lieblingsspiele an. Es ist notwendig zu bestimmen, welche Spiele bei einer Gruppe von Teilnehmern beliebt, bei einer anderen jedoch nicht beliebt sind. Mit anderen Worten: Sie müssen die symmetrische Differenz der Mengen der Lieblingsspiele zweier Gruppen finden.
Eingabeformat
Zuerst die Anzahl & nbsp;
Die Anzahl & nbsp;
n & nbsp; - die Anzahl der Teilnehmer der ersten Gruppe. Dann & nbsp; n & nbsp; Zeilen, jede enthält die Namen der Lieblingsspiele eines Teilnehmers, getrennt durch Leerzeichen. Die Anzahl & nbsp;
m & nbsp; - die Anzahl der Teilnehmer der zweiten Gruppe. Dann & nbsp; m & nbsp; Zeilen, jede enthält die Namen der Lieblingsspiele eines Teilnehmers, getrennt durch Leerzeichen. Ausgabeformat
die Namen der Spiele auszugeben, die nur in einer der Gruppen vorkommen (symmetrische Differenz der Mengen), in alphabetischer Reihenfolge, getrennt durch Leerzeichen
Beispiel
Eingabe
3
Ticket_to_Ride Kolonialisten
Ticket_to_Ride 7_WUNDER
CARCASSON IMADGINARIUM
MANKHKIN
7_WUNDER DISSITS
Ausgabe
ticket_to_ride dixit imaginarium kardasson Mantle
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
