Question

Поиск подстроки. Пайтон. Даны 2 строки. Необходимо найти индекс второго вхождения искомой строки в строке для поиска. Разберем самый первый пример, когда необходимо найти второе вхождение "s" в слове "sims". Если бы нам надо было найти ее первое вхождение, то тут все просто: с помощью функции index или find мы можем узнать, что "s" – это самый первый символ в слове "sims", а значит индекс первого вхождения равен 0. Но нам необходимо найти вторую "s", а она 4-ая по счету. Значит индекс второго вхождения (и ответ на вопрос) равен 3. Строка, которую нужно найти, может состоять из нескольких символов. Input: Две строки (String). Output: Int or None Примеры: second_index("sims", "s") => 3 second_index("find the river", "e") => 12 second_index("hi", "h") => None

Answer 1

Решение:

def second_index(world, string):

return None if world.count(string) < 2 or len(string) > 1 else world.replace(string, ' ', 1).index(string)

# Возвращаем None если введённая строка string встречается в слове 1 раз и если длина введённой строки string больше 1. В противном случаем возвращаем индекс второго вхождения строки string (первое вхождение заменяем на ' ')

world = input()

string = input()

second_index(world, string)

Answer 2

Problem Description

The task is to find the index of the second occurrence of a given substring within a string. Let's consider the first example, where we need to find the second occurrence of the letter "s" in the word "sims". If we were looking for the first occurrence, we could simply use the `index` or `find` function to determine that "s" is the first character in the word "sims", and therefore the index of the first occurrence is 0. However, we need to find the second "s", which is the fourth character in the word. Hence, the index of the second occurrence (and the answer to the question) is 3.

Solution in Python

To solve this problem in Python, we can use the `find` method of the string. The `find` method returns the index of the first occurrence of a substring within a string. We can use this method twice to find the index of the second occurrence.

Here's the Python code to find the index of the second occurrence of a substring within a string:

def second_index(string, substring):
    first_index = string.find(substring)
    if first_index == -1:
        return None
    second_index = string.find(substring, first_index + 1)
    if second_index == -1:
        return None
    return second_index

Let's go through the code step by step: 1. We first find the index of the first occurrence of the substring using the `find` method and store it in the variable `first_index`. 2. If the `find` method returns -1, it means the substring is not found in the string, so we return `None`. 3. We then use the `find` method again, but this time we start searching from the index after the first occurrence (`first_index + 1`). This ensures that we find the second occurrence and not the first occurrence again. 4. If the `find` method returns -1 again, it means the second occurrence is not found, so we return `None`. 5. Otherwise, we return the index of the second occurrence.

Examples

Let's test the `second_index` function with the provided examples:

print(second_index("sims", "s"))  # Output: 3
print(second_index("find the river", "e"))  # Output: 12
print(second_index("hi", "h"))  # Output: None

The first example returns 3 because the second occurrence of "s" in "sims" is at index 3. The second example returns 12 because the second occurrence of "e" in "find the river" is at index 12. The third example returns None because there is no second occurrence of "h" in "hi".

I hope this helps! Let me know if you have any further questions.