String and Frequency Fun with Alice the Cryptographer

Hello! Are you ready for an exciting journey into the world of strings and frequency analysis? Today, we’ll assist Alice, an aspiring cryptographer, with a fascinating task involving string transformations and calculations. Alice has developed a unique encoding scheme that shifts letters in the alphabet and analyzes their occurrences.

This should be a fun and insightful challenge that hones your problem-solving and coding skills. Let’s dive in!

Alice's encoding scheme involves two steps. First, she takes a word and shifts each character to the next one alphabetically. For example:

• 'a' becomes 'b'
• 'z' becomes 'a'

Next, Alice analyzes the frequency of each character in the transformed string. For each unique character, she calculates a product of its ASCII value and its frequency. Finally, she sorts these products in descending order.

Your task is to implement a Ruby method, character_frequency_encoding(word), that performs Alice’s encoding and returns the sorted list of products.

For example:

word = "banana"

The method should return:

[294, 222, 99]

Here’s how the process works:

1. Transform "banana" into "cbobob".
2. Calculate the products:
   • 'c': ASCII value 99, frequency 1, product 99 × 1 = 99.
   • 'b': ASCII value 98, frequency 3, product 98 × 3 = 294.
   • 'o': ASCII value 111, frequency 2, product 111 × 2 = 222.
3. Sort the products in descending order: [294, 222, 99].

To implement Alice’s encoding scheme, we start by shifting each character to the next in the alphabet. Using Ruby’s each_char method, we iterate over the string and transform each character.

def character_frequency_encoding(word)
  # Shift each character to the next in the alphabet
  shifted_chars = word.each_char.map do |letter|
    if letter == 'z'
      'a' # Wrap around for 'z'
    else
      (letter.ord + 1).chr # Shift to the next character
    end
  end

At this stage, shifted_chars for "banana" will be ["c", "b", "o", "b", "o", "b"]. This array represents the transformed characters.

Next, we calculate the frequency of each character in the transformed array. By initializing a hash with a default value of 0, we can easily count occurrences as we iterate through the array of shifted characters.

  # Initialize a frequency hash
  frequency_hash = Hash.new(0)

  # Count the frequency of each character
  shifted_chars.each do |letter|
    frequency_hash[letter] += 1
  end

The frequency_hash now holds the counts of each character. For "banana", it will be:

{"c" => 1, "b" => 3, "o" => 2}