题解 | 字符串加解密

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine()) { // 注意 while 处理多个 case
            // int a = in.nextInt();
            // int b = in.nextInt();
            // System.out.println(a + b);
            String s = in.nextLine();
            String t = in.nextLine();

            System.out.println(encrypt(s));
            System.out.println(decrypt(t));
        }
    }

    private static String encrypt(String s) {
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            char tmp;
            if (Character.isLetter(c)) {
                if (c == 'Z') {
                    tmp = 'A';
                } else if (c == 'z') {
                    tmp = 'a';
                } else {
                    tmp = (char) (c+1);
                }
                
                if (Character.isUpperCase(c)) {
                    tmp = Character.toLowerCase(tmp);
                } else {
                    tmp = Character.toUpperCase(tmp);
                }
            } else {
                if (c == '9') {
                    tmp = '0';
                } else {
                    tmp = (char) (c+1);
                }
            }
            sb.append(tmp);
        }
        return sb.toString();
    }

    private static String decrypt(String s) {
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            char tmp;
            if (Character.isLetter(c)) {
                if (c == 'A') {
                    tmp = 'Z';
                } else if (c == 'a') {
                    tmp = 'z';
                } else {
                    tmp = (char) (c-1);
                }
                
                if (Character.isUpperCase(c)) {
                    tmp = Character.toLowerCase(tmp);
                } else {
                    tmp = Character.toUpperCase(tmp);
                }
            } else {
                if (c == '0') {
                    tmp = '9';
                } else {
                    tmp = (char) (c-1);
                }
            }
            sb.append(tmp);
        }
        return sb.toString();
    }
}