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🎉 ¡Felicidades! 🎉
¡Has resuelto la tarea brillantemente! Era un reto difícil, pero encontraste la solución correcta. ¡Estás un paso más cerca de dominar la programación! Sigue así, cada etapa superada te hace más fuerte.
Lección 3. FOR cycle
Dificultad:
Tarea«Elementos vecinos»
💻 Python
Se instala un nuevo escáner de paquetes en la fábrica. Revisa el lote uno tras otro. Tú — El programador, a quien se le indica que escriba un programa para él.
El programa primero recibe el número de paquetes en el lote ( n ). Luego comienza a recibir los códigos enteros de cada paquete uno a la vez.
El escáner funciona según las siguientes reglas:
- Si el código del paquete — es un número negativo, esto se considera un error de escaneo. Dicho paquete debe ignorarse, se muestra el mensaje "Código incorrecto, pase." e inmediatamente pasar al siguiente paquete.
- Si el código del paquete es divisible por 13 sin resto (por ejemplo, 0, 13, 26, ...), entonces el paquete se considera peligroso. Es necesario detener inmediatamente toda la revisión, mostrar el mensaje "Se encontró un paquete peligroso con el código:
[código]! La revisión se detiene." y finalizar el programa. - Si el código del paquete — es un número normal, no negativo que no es divisible por 13, entonces su valor se suma al valor total de todos los paquetes revisados.
- Si se revisó todo el lote y no se encontró ningún paquete peligroso, el programa debe mostrar el mensaje "La revisión está completa. El valor total de los paquetes:
[suma]."
Formato de entrada
La primera línea contiene un número entero & nbsp; n & nbsp; (1 & le; n & le; 100) & mdash; La cantidad de paquetes en el lote.
Las siguientes & nbsp; n líneas contienen un número entero & mdash; El código del siguiente paquete.
Formato de salida
el programa muestra uno o más mensajes dependiendo de los códigos de los paquetes:
- con código negativo:
código incorrecto, pase. - cuando se detecta un paquete peligroso:
se encontró un paquete peligroso con código: [code]! La auditoría se detiene.(donde
[code] — es el código en sí). - Si la verificación se ha completado con éxito:
La verificación está completa. El valor total de los paquetes: [sum].(donde
[sum] — es el monto total del valor).
Ejemplo
Entrada
5
10
-5
20
15
2
Salida
Código incorrecto, pasar.
La verificación está completa. Valor general de los paquetes: 47.
Pista
Basics of the forcycle
The for loop in Python is your main tool for iterating through elements in any sequence. Imagine that you have a box with different items. The for loop allows you to take one item at a time, do something with it, and move on to the next until the items in the box run out.
It is used to iterate over sequences such as lists, strings, tuples, sets, or even keys in a dictionary. The same block of code is executed for each element of the sequence.
Syntax:
for element in sequence:
# a block of code that will be executed for each element
# IMPORTANT: this block must be indented!
Here, the element is a temporary variable that is assigned a different value from the sequence at each iteration. You can name this variable any way you want, but it's better to choose a meaningful name (for example, fruit for a list of fruits or letter for a string).
Iterating through the list
A list is an ordered collection of items. The for loop will run through it from the first element to the last.
fruits = ['apple', 'banana', 'cherry']
for fruit in fruit:
print(fruit)
Conclusion:
apple
banana
cherry
Iterating over the line
A string is, in fact, a sequence of characters. Therefore, the for loop can iterate over it just as easily.
word = "Python"
for a letter in a word:
print(letter)
Conclusion:
P
y
t
h
o
n
Cycle control: break and continue
Sometimes you don't have to go through the whole cycle to the end. There are special operators for this.
The break operator
The break operator is used to immediately and completely terminate the loop. As soon as the program encounters a break, it immediately exits the loop and continues execution from the next line of code after it.
A useful tip: break is indispensable when you are looking for something. Once you've found what you're looking for, there's no point in continuing the search.
Example: We have a list of numbers, and we want to find the first even number and stop the loop as soon as it is found.
numbers = [1, 3, 5, 6, 7, 9, 10]
for num in numbers:
if num % 2 == 0: # Check for parity
print(f"The first even number is found: {num}")
break # Immediately exit the loop
print("The loop is completed.")
Conclusion:
The first even number was found: 6
The cycle is completed.
Please note that the numbers 7, 9, and 10 were not checked, as the cycle was interrupted by the number 6.
The continue operator
The continue operator is used to skip the current iteration and immediately move on to the next one. All the code that is in the loop after continue will not be executed for the current element.
A useful tip: continue is very convenient for "filtering" data inside a loop. If the current item doesn't suit you by some criterion, you just skip it and move on to the next one.
Example: We have a list of numbers, and we want to output all the numbers except the even ones.
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for num in numbers:
if num % 2 == 0: # Check for parity
continue # If the number is even, skip print() and go to the next number.
print(num)
Conclusion:
1
3
5
7
9
When num was equal to 2, 4, 6, etc., the if condition was met, continue skipped the print(num) command, and the loop immediately started a new iteration.
The difference between break and continue is in a nutshell
break: "Stop, car!". Stops the cycle completely.continue: "This one doesn't fit, let's do the next one!". Skips only the current step.
The else block in the for
loop
The for loop may have an optional else block. This block is executed only if the loop has completed all its iterations naturally, that is, it has not been interrupted by the break operator.
A useful tip: It is a very powerful tool for search tasks. The else block makes it easy to handle a situation where the search has ended but nothing has been found.
Example 1: The loop ended normally
for number in range(3):
print(number)
else:
print("The cycle is completed without interruptions.")
Conclusion:
0
1
2
The cycle is completed without interruptions.
Example 2: The loop is interrupted by the break
for number in range(3):
if number == 1:
print("We found 1, we break the loop.")
break
print(number)
else:
# This block will not be executed because there was a break
print("The cycle is completed without interruptions.")
Conclusion:
0
We found 1, we interrupt the cycle.
Practical examples
The sum of all the numbers in the list
This is a classic task for understanding how to work with a cycle and accumulate results.
numbers = [1, 2, 3, 4, 5]
amount = 0 # Initialize the variable to store the amount BEFORE the loop
for a number in numbers:
sum += number # At each iteration, we add the current number to the total
print(f' Sum: {sum}') # Output the final result AFTER the loop
Conclusion: Amount: 15
A useful tip: Although this method perfectly demonstrates how the loop works, in real code it is better to use the built-in sum() function to find the sum of the list elements: print(sum(numbers)). It's shorter and more efficient.
Finding the maximum number in the list
Here we assume that the first element is the maximum, and then in the loop we compare it with all the others.
numbers = [1, 7, 3, 9, 5]
maximum = numbers[0] # We take the first element as the temporary maximum
for a number in numbers:
if the number is > maximum: # If we find a number greater than our maximum...
maximum = number # ...then we update the maximum
print(f' Maximum: {maximum}')
Conclusion: Maximum: 9
A useful tip: As with the sum, Python has a built-in function max() for this task: print(max(numbers)). Knowing these functions saves time, but understanding how they work using the for loop is a key skill for a programmer.
main.py
Prueba 1
Prueba 2
Prueba 3
Prueba 4
Prueba 5
Prueba 6
Prueba 7
Prueba 8
Prueba 9
Prueba 10
Solución del desarrollador
# Сначала считываем количество посылок в партии
num_packages = int(input())
# Инициализируем переменную для хранения общей ценности
total_value = 0
# Запускаем цикл for, который будет выполняться num_packages раз
for _ in range(num_packages):
# Считываем код очередной посылки
package_code = int(input())
# 1. Проверяем на ошибку сканирования (отрицательный код)
if package_code < 0:
print("Неверный код, пропуск.")
# Пропускаем остаток кода и переходим к следующей итерации
continue
# 2. Проверяем, не является ли посылка опасной
if package_code % 13 == 0:
print(f"Обнаружена опасная посылка с кодом: {package_code}! Проверка остановлена.")
# Немедленно выходим из цикла
break
# 3. Если посылка обычная, добавляем ее ценность к общей сумме
total_value = total_value + package_code
# 4. Этот блок выполнится, только если цикл for завершился без break
else:
print(f"Проверка завершена. Общая ценность посылок: {total_value}.")
