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Leçon 7. Two -dimensional arrays
Difficulté :
Exercice«Dépenses mensuelles»
💻 Python
Vous travaillez comme analyste dans une petite famille et souhaitez automatiser le processus de calcul des dépenses mensuelles en produits. Vous disposez d'un tableau qui est une matrice où chaque ligne correspond à une semaine du mois, et chaque colonne & ndash; à un jour de la semaine. Chaque cellule indique le montant dépensé en produits ce jour-là. Votre tâche & ndash; est d'écrire un programme qui accepte ce tableau en entrée et calcule le montant total des dépenses en produits pour le mois.
Format d entrée
La première ligne contient deux entiers & nbsp;
n & nbsp; m , séparés par un espace, où & nbsp; n & nbsp; & ndash; Le nombre de semaines dans un mois (nombre de lignes de la matrice), et & nbsp; m & nbsp; & ndash; Le nombre de jours dans la semaine (nombre de colonnes de la matrice). Les & nbsp; n & nbsp; lignes suivantes contiennent chacune & nbsp; m & nbsp; entiers séparés par des espaces, qui constituent une matrice des produits Format de sortie
un nombre & ndash; Le montant total des dépenses alimentaires par mois
Exemple
Entrée
3 7
100 50 75 120 80 60 90
110 40 65 130 90 70 100
90 60 85 110 70 50 80
Sortie
1955
Indice
min function
The min() function is your tool for quickly searching for the smallest element of several values or within a collection.
Syntax
min(iterable, *[, key, default])
min(arg1, arg2, *args[, key])
iterable: An iterable object (for example, a list, tuple, string, set).arg1, arg2, *args: One or more arguments passed directly for comparison.key(optional): A function that is applied to each element before comparison. The minimum will be searched based on the results of this function.default(optional): The value that will be returned ifiterableis empty. Ifdefaultis not specified, an attempt to find the minimum in an empty collection will cause the errorValueError.
Usage examples
-
With a single iterable object:
numbers = [3, 1, 4, 1, 5, 9] print(min(numbers)) # Output: 1 -
With multiple arguments:
print(min(3, 1, 4, 1, 5, 9)) # Output: 1 -
With the
keyparameter: Searching for an element by any of its properties.words = ["apple", "banana", "cherry"] # Finding the word with the shortest length print(min(words, key=len)) # Output: 'apple' -
With the
defaultparameter: Safe handling of potentially empty collections.empty_list = [] print(min(empty_list, default="empty")) # Output: 'empty'
Useful tips and subtleties:
- Comparing different types: Incomparable data types, such as a number and a string, cannot be compared.
min(5, "hello")will cause the errorTypeError. - How the
keyworks: It is important to understand thatkeyonly changes the value for comparison, but returns the original element. In the examplemin(words, key=len), the lengths (5, 6, 6) are compared, but the word 'apple' itself is returned. - Using
lambdafunctions withkey: For complex comparisons, it is convenient to use anonymouslambdafunctions. For example, to find a dictionary with the minimum value by the key 'age':people = [{'name': 'John', 'age': 25}, {'name': 'Jane', 'age': 22}] print(min(people, key=lambda person: person['age'])) # Output: {'name': 'Jane', 'age': 22} - String comparison: The strings are compared lexicographically (in alphabetical order).
min("a", "b", "A")returns'A', since capital letters have a smaller code in the symbol table.
Function max()
The max() function works similarly to min(), but returns the largest element from the passed arguments or collection.
Syntax
max(iterable, *[, key, default])
max(arg1, arg2, *args[, key])
The parameters (iterable, arg1, arg2, *args, key, default) have the same value as in the min() function.
Usage examples
-
With a single iterable object:
numbers = [3, 1, 4, 1, 5, 9] print(max(numbers)) # Output: 9 -
With multiple arguments:
print(max(3, 1, 4, 1, 5, 9)) # Output: 9 -
With the
keyparameter:words = ["apple", "banana", "cherry"] # Finding the word with the longest length print(max(words, key=len)) # Output: 'banana' -
With the
defaultparameter:empty_list = [] print(max(empty_list, default='N/A')) # Output: 'N/A'
Useful tips and subtleties:
- All the tips and subtleties applicable to
min()are also relevant formax(): avoid mixing types, uselambdafunctions for complex keys and keep in mind thedefault parameterfor empty collections. - If there are several identical maximum/minimum elements, the first one is returned. In the example,
max(words, key=len)the words "banana" and "cherry" have the same length of 6, butmaxreturns the first encountered 'banana'.
Function sum()
The sum() function is used to find the sum of numeric elements in an iterable object.
Syntax
sum(iterable, start=0)
iterable: An iterable object containing numbers (for example, a list, a tuple, a set).start(optional): The initial value that is added to the total amount. The default value is 0.
Usage examples
-
Sum of list/tuple/set elements:
numbers_list = [1, 2, 3, 4, 5] print(sum(numbers_list)) # Output: 15 -
Using the
startparameter:numbers = [1, 2, 3, 4, 5] # We start summing not from 0, but from 10 total = sum(numbers, 10) print(total) # Output: 25 (10 + 1 + 2 + 3 + 4 + 5)
Application to two-dimensional arrays (lists of lists)
sum() can be effectively used to process matrices, but with one important caveat.
- Wrong approach:
sum(matrix)will cause the errorTypeError, as Python will try to add the initial value0with the list[1, 2, 3]. - The right approach: You must first calculate the sum of each row, and then add these amounts.
# Two-dimensional array matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ] # Sum of all array elements using a generator total_sum = sum(sum(row) for row in matrix) print(total_sum) # Output: 45
Useful tips and subtleties:
- For numbers only:
sum()only works with numeric types (int, float). An attempt to summarize a list of strings (sum(["a", "b"])) will result in aTypeError. - Summation
True/False:Trueis interpreted as1, andFalseas0. This can be used to count the true values in the collection.bools = [True, False, True, True] # 1 + 0 + 1 + 1 print(sum(bools)) # Output: 3 - "Flattening" the list of lists: The
startparameter can be cunningly used to combine lists, although it is less readable and efficient than other methods.
Warning: This method is not recommended for large lists due to poor performance.list_of_lists = [[1, 2], [3, 4], [5]] flat_list = sum(list_of_lists, []) print(flat_list) # Output: [1, 2, 3, 4, 5]
main.py
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
Test 8
Test 9
Test 10
Solution du développeur
