题解 | #字符串加密#

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {

    private static String ABC = "abcdefghijklmnopqrstuvwxyz";

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String key = in.nextLine();
        String words = build(key); //利用ABC字母表和key秘钥构建新字母表words
        Map<Character,Character> map = new TreeMap<>(); 
        for(int i=0; i<ABC.length(); i++){
            map.put(ABC.charAt(i), words.charAt(i)); //上行：ABC字母表  下行：words新字母表
        }
        String str = in.nextLine();
        String res = encode(str, map);
        System.out.println(res);
    }

    private static String build(String s){
        //字符串字母去重
        StringBuffer sb = new StringBuffer();
        for(int i=0; i<s.length(); i++){
            char c = s.charAt(i);
            if(sb.indexOf(String.valueOf(c)) == -1) sb.append(c);
        }
        s = sb.toString();
        //26字母去s重
        StringBuffer sb2 = new StringBuffer();
        for(int i=0; i<ABC.length(); i++){
            char c2 = ABC.charAt(i);
            if(!s.contains(String.valueOf(c2))) sb2.append(c2);
        }
        String temp = sb2.toString();
        //s拼接去重后“26字母”
        return s + temp;
    }

    private static String encode(String s, Map<Character, Character> map){
        //注意：被加密s中字符的大小写顺序保持不变
        //s作为查找key，获取map中对应的value
        StringBuffer sb = new StringBuffer();
        for(int i=0; i<s.length(); i++){
            char k = s.charAt(i);
            if(Character.isUpperCase(k)){
                k = Character.toLowerCase(k);
                char v = map.get(k);
                sb.append(Character.toUpperCase(v));
            }else if(Character.isLowerCase(k)){
                sb.append(map.get(k));
            }else {
                sb.append(k); //空格
            }
        }
        return sb.toString();
    }
  
}