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
            String a = in.nextLine();
            String b = in.nextLine();
            System.out.println(encode(a));
            System.out.println(decode(b));
        }
    }

    private static String decode(String source) {
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < source.length(); i++) {
            char c = source.charAt(i);
            if (Character.isLetter(c)) {
                builder.append(move(c, -1));
                continue;
            } else if (Character.isDigit(c)) {
                int value = Integer.parseInt(source.substring(i, i + 1));
                builder.append((value + 9) % 10);
            } else {
                builder.append(c);
            }
        }
        return builder.toString();
    }

    private static String encode(String source) {
        /*
        加密方法为：
           当内容是英文字母时则用该英文字母的后一个字母替换，同时字母变换大小写,如字母a时则替换为B；字母Z时则替换为a；
           当内容是数字时则把该数字加1，如0替换1，1替换2，9替换0；
           其他字符不做变化。
         */

        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < source.length(); i++) {
            char c = source.charAt(i);
            if (Character.isLetter(c)) {
                builder.append(move(c, 1));
                continue;
            } else if (Character.isDigit(c)) {
                int value = Integer.parseInt(source.substring(i, i + 1));
                builder.append((value + 1) % 10);
            } else {
                builder.append(c);
            }
        }
        return builder.toString();
    }

    private static Character move(Character c, int i) {
        //左移
        if (i < 0) {
            Character cn = c;
            if (c == 'a' || c == 'A') {
                cn = 'Z';
            } else {
                cn = (char) (c - 1);
            }
            return Character.isLowerCase(c) ? Character.toUpperCase(
                       cn) : Character.toLowerCase(cn);
        }
        //右边移动
        else {
            Character cn = c;
            if (c == 'z' || c == 'Z') {
                cn = 'a';
            } else {
                cn = (char) (c + 1);
            }
            return Character.isLowerCase(c) ? Character.toUpperCase(
                       cn) : Character.toLowerCase(cn);
        }
    }
}