Find the K-th Character in String Game I

Alice and Bob are playing a game. Initially, Alice has a string word = "a".

You are given a positive integer k.

Now Bob will ask Alice to perform the following operation forever:

• Generate a new string by changing each character in word to its next character in the English alphabet, and append it to the original word.

For example, performing the operation on "c" generates "cd" and performing the operation on "zb" generates "zbac".

Return the value of the k<sup>th</sup> character in word, after enough operations have been done for word to have at least k characters.

Note that the character 'z' can be changed to 'a' in the operation.

LeetCode Problem - 3304

class Solution {

    // Method to find the k-th character in a string generated by repeating a transformation process starting from "a"
    public char kthCharacter(int k) {
        String start = "a";  // Initial string is "a"
        if (k == 1) return 'a';  // If k is 1, return 'a' as it's the first character

        char ans = '1';  // Initialize the result character

        // Continuously create new strings until the length of the string is at least k
        while (true) {
            start = createNewString(start);  // Generate the new string by transforming the current string

            // If the newly generated string is long enough, extract the k-th character
            if (start.length() >= k) {
                ans = start.charAt(k - 1);  // Get the k-th character (0-based index)
                break;  // Exit the loop once the answer is found
            }
        }

        return ans;  // Return the k-th character
    }

    // Helper method to create a new string by transforming the given string
    public String createNewString(String str) {
        StringBuilder sb = new StringBuilder(str);  // Use StringBuilder for efficient string concatenation

        // Iterate over each character in the original string
        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);  // Get the current character

            // If the character is 'z', append 'a' to the new string, otherwise append the next character
            if (ch == 'z') {
                sb.append('a');
            } else {
                sb.append((char)(ch + 1));  // Increment the character to the next alphabet letter
            }
        }

        return sb.toString();  // Return the newly generated string
    }
}