Untitled

public class CaesarCipherDecoder {

    public static String decodeMessage(String encodedMessage, int n) {
        String decodedMessage = "";
        
        // Calculate the sum of positions of letters
        int sumOfPositions = 0;
        for (int i = 0; i < encodedMessage.length(); i++) {
            char ch = encodedMessage.charAt(i);
            if (Character.isLetter(ch)) {
                sumOfPositions += getCharacterPosition(ch);
            }
        }

        // Reduce the sum to a single digit
        int reducedSum = reduceToSingleDigit(sumOfPositions);

        // Add the decoding number (n)
        int finalValue = reducedSum + n;

        // Wrap the finalValue around to stay between 1 and 9
        if (finalValue < 1) {
            finalValue = 9 + finalValue;
        } else if (finalValue > 9) {
            finalValue = finalValue % 9;
        }

        // Decode the message by subtracting finalValue from each letter's position
        for (int i = 0; i < encodedMessage.length(); i++) {
            char ch = encodedMessage.charAt(i);
            if (Character.isLetter(ch)) {
                decodedMessage += decodeCharacter(ch, finalValue);
            } else {
                decodedMessage += ch;
            }
        }

        return decodedMessage;
    }

    // Get the position of the character in the alphabet (A=1, Z=26)
    private static int getCharacterPosition(char ch) {
        if (Character.isUpperCase(ch)) {
            return ch - 'A' + 1;
        } else {
            return ch - 'a' + 1;
        }
    }

    // Reduce a number to a single digit by summing its digits
    private static int reduceToSingleDigit(int number) {
        while (number >= 10) {
            number = sumDigits(number);
        }
        return number;
    }

    // Helper method to sum digits of a number
    private static int sumDigits(int number) {
        int sum = 0;
        while (number > 0) {
            sum += number % 10;
            number /= 10;
        }
        return sum;
    }

    // Decode a single character based on the final value
    private static char decodeCharacter(char ch, int finalValue) {
        int position = getCharacterPosition(ch);
        
        // Subtract the finalValue from the position
        int newPosition = position - finalValue;

        // Wrap the position around if necessary
        if (newPosition < 1) {
            newPosition = 26 + newPosition;
        }

        // Return the decoded character
        if (Character.isUpperCase(ch)) {
            return (char) ('A' + newPosition - 1);
        } else {
            return (char) ('a' + newPosition - 1);
        }
    }

    public static void main(String[] args) {
        // Input and decoding number
        String encodedMessage = "Zkrkxoq Gigjkse";
        int decodingNumber = -21;

        // Decoding the message
        String decodedMessage = decodeMessage(encodedMessage, decodingNumber);
        System.out.println("Decoded Message: " + decodedMessage);
    }
}