Hello! Are you ready for an exciting voyage into the wonderful realm of strings and data structures? Today, we will be assisting Alice, an aspiring cryptographer, with an intriguing string manipulation task. She loves playing with strings and has come up with a unique string encoding scheme. I assure you, this will be an enlightening journey that will stretch your programming muscles. Let's get started!

Alice has devised a unique way of encoding words. She takes a word and replaces each character with the next character in the alphabetical order. In other words, given a string word, for each character, if it's not z, she replaces it with the character that comes next alphabetically. For the character z, she replaces it with a.

Another element of Alice's algorithm involves frequency analysis. After shifting the characters, she counts the frequency of each character in the new string. Then, she creates an association of each character with its frequency and ASCII value. Each character maps to a number, which is a product of the ASCII value of the character and its frequency. The aim of our task is to construct a list that contains these products, sorted in descending order.

Example

For the input string "banana", the output should be [294, 222, 99].

The string "banana" will be shifted to "cbobob".

Calculating the product of frequency and ASCII value for each character:

• The ASCII value for c is 99. It appears once in the string, so its product is 99 * 1 = 99.
• The ASCII value for b is 98. It appears three times in the string, so its product is 98 * 3 = 294.
• The ASCII value for o is 111. It appears twice in the string, so its product is 111 * 2 = 222.

Collecting these products into a list gives [99, 294, 222]. Sorting this list in descending order results in [294, 222, 99].

Our first step involves mapping each character of the input string to the next alphabetical character. For this, we define the nextString as an empty StringBuilder object, storing the result of the shift operation. We then iterate over each character of the input string. If a character is not z, we replace it with the next alphabetical character using Scala's .toInt and .toChar methods. If it is z, we replace it with a.

Here's the updated function:

Scala
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1import scala.collection.mutable
2
3def characterFrequencyEncoding(word: String): List[Int] = {
4  val nextString = new StringBuilder
5  for (letter <- word) {
6    nextString.append(if (letter == 'z') 'a' else (letter.toInt + 1).toChar)
7  }
8  nextString.toString()
9}

The next step is to track the frequency of each character in nextString. We start by initializing a mutable map, frequencyMap. Then, we iterate over nextString. If the current character exists in frequencyMap, we increment its frequency by 1. If it doesn't exist, we add it to frequencyMap with a frequency of 1.

Incorporating this step into the function, our code now looks like this:

Scala
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1def characterFrequencyEncoding(word: String): List[Int] = {
2  val nextString = new StringBuilder
3  for (letter <- word) {
4    nextString.append(if (letter == 'z') 'a' else (letter.toInt + 1).toChar)
5  }
6  val frequencyMap = mutable.Map[Char, Int]().withDefaultValue(0)
7  for (letter <- nextString) {
8    frequencyMap(letter) += 1
9  }
10  frequencyMap
11}

Next, we calculate the numerical representation for each unique character. We initialize an empty list, combinedValues, to store these numbers. For each character in frequencyMap, we calculate the product of its ASCII representation and its frequency in nextString and append this to combinedValues.

Here's the updated function:

Scala
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1def characterFrequencyEncoding(word: String): List[Int] = {
2  val nextString = new StringBuilder
3  for (letter <- word) {
4    nextString.append(if (letter == 'z') 'a' else (letter.toInt + 1).toChar)
5  }
6  val frequencyMap = mutable.Map[Char, Int]().withDefaultValue(0)
7  for (letter <- nextString) {
8    frequencyMap(letter) += 1
9  }
10  val combinedValues = frequencyMap.map { case (letter, freq) =>
11    letter.toInt * freq
12  }.toList
13  combinedValues
14}

The final step is to sort the list combinedValues in descending order. We use Scala's .sorted with a custom ordering function. Here's our complete function:

Scala
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1def characterFrequencyEncoding(word: String): List[Int] = {
2  val nextString = new StringBuilder
3  for (letter <- word) {
4    nextString.append(if (letter == 'z') 'a' else (letter.toInt + 1).toChar)
5  }
6  val frequencyMap = mutable.Map[Char, Int]().withDefaultValue(0)
7  for (letter <- nextString) {
8    frequencyMap(letter) += 1
9  }
10  val combinedValues = frequencyMap.map { case (letter, freq) =>
11    letter.toInt * freq
12  }.toList
13  combinedValues.sorted(Ordering[Int].reverse)
14}

Well done! You've successfully tackled an intricate problem, which required you to exercise multiple topics such as string manipulation, map processing, and list sorting in Scala. This task underscored the importance of reusing already calculated values. I encourage you to apply what you've learned today to other tasks. There are many more exciting challenges waiting for you in the upcoming practice sessions. Happy coding!