Caesar Cipher

/*
 * Problem : Shift letters.
 * Input   : A word and a shift.
 * Output  : The shifted word.
 * Approach: Alphabet arithmetic.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(String a, String b) {
        // Step 1: The shift arrives as text. Convert it to a number. Only the remainder after 26 matters.
        int shift = (int) (Long.parseLong(b) % 26);
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < a.length(); i++) {
            char letter = a.charAt(i);

            // Step 2: Move a letter inside its own range (A-Z or a-z). Use the first letter of the range as the base.
            if (letter >= 'A' && letter <= 'Z') {
                result.append((char) ('A' + (letter - 'A' + shift) % 26));
            } else if (letter >= 'a' && letter <= 'z') {
                result.append((char) ('a' + (letter - 'a' + shift) % 26));
            } else {
                // Step 3: Other characters stay the same.
                result.append(letter);
            }
        }
        return result.toString();
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String a = scanner.next();
        String b = scanner.next();
        System.out.println(solve(a, b));
    }
}