Lesson 3

Welcome to today's session, where we are embarking on a journey into the mystical territory of combined string and array operations. Have you ever thought about how to update a string and an array in parallel while a specific condition holds true? That's precisely what we'll explore today, all in the context of a real-world scenario related to a mystery novel book club. Get ready to dive in!

Our mission for today is to generate a unique encoded message for a book club. Here's the fun part: to create a cryptic message, we will process a string and an array of numbers simultaneously and stop once a given condition is satisfied.

For the string, our task is to replace each letter with the next alphabetical letter and then reverse the entire updated string. For the array of numbers, our task is to divide each number by 2, round the result, and accumulate the rounded numbers until their total exceeds 20.

When the accumulated total exceeds 20, we immediately stop the process and return the updated string and the as yet unprocessed numbers in their original order.

**Example**

Consider the input string `"books"`

and array `[10, 20, 30, 50, 100]`

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We start our process with an empty string and a sum of `0`

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- For the first character 'b' in 'books', we replace it with the next alphabet 'c'. For the corresponding number 10 in the array, we divide it by 2 and round it. The result is 5. The sum after first operation is 5 which is less than 20, so we continue to the next character.
- For the next character 'o', we replace it with 'p'. And for the corresponding number 20 in the array, half and rounded is 10. The sum after the second operation is 15 (5 + 10). The sum still doesn't exceed 20, so we move to third character.
- For the next character 'o', we replace it with 'p'. And for the corresponding number 30 in the array, half and rounded is 15. When we add this '15' to our previously calculated sum 15, it totals to 30 which is more than 20. So, we stop the process here.
- We have processed 'b', 'o', and 'o' from the word 'books' and replaced them with 'c', 'p', and 'p' respectively to get "cpp". After reversing, we get "ppc".
- For the array, we exclude any numbers that we have processed. Hence, we exclude the first three numbers and the array becomes [50, 100].

So the output should be `('ppc', [50, 100])`

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Let's begin our journey by setting up two crucial components: our resultant string and a variable to keep track of the cumulative sum.

Python`1def solution(inputString, numbers): 2 result = '' 3 sum_so_far = 0`

With the setup complete, it's time to roll up our sleeves and process the string and array. We need to iterate over the `inputString`

and update each character to its next alphabetical character. Simultaneously, we'll keep tabs on our array condition - if the sum of half of the numbers crosses our threshold of 20, we should stop the process.

Python`1def solution(inputString, numbers): 2 result = '' 3 sum_so_far = 0 4 i = 0 5 while i < len(inputString) and sum_so_far <= 20: 6 result += 'a' if inputString[i] == 'z' else chr(ord(inputString[i]) + 1) 7 half_number = round(numbers[i] / 2) 8 sum_so_far += half_number 9 i += 1`

With the updates complete, we're one step away from solving this mystery. We must reverse our string to generate the final encoded message! At the end, we return the processed string and the remaining array.

Python`1def solution(inputString, numbers): 2 result = '' 3 sum_so_far = 0 4 i = 0 5 while i < len(inputString) and sum_so_far <= 20: 6 result += 'a' if inputString[i] == 'z' else chr(ord(inputString[i]) + 1) 7 half_number = round(numbers[i] / 2) 8 sum_so_far += half_number 9 i += 1 10 return result[::-1], numbers[i:]`

Congratulations! You have successfully navigated and implemented a complex process that involved string manipulation, array processing, and cumulative conditions. This computational challenge has given you the perspective on how to apply these programming elements in real-world scenarios.

Up next, I encourage you to solve more problems that require you to iterate and update arrays based on certain conditions. We will meet again soon to crack another problem and delve deeper into the world of coding. Keep practising and happy coding!