题解 | #字符串合并处理#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String str1 = sc.next();
            String str2 = sc.next();
            System.out.println(mergeAndSortChange(str1,str2));
        }


    }

    //对字符串进行 1前后合并 2排序 3指定字符转换
    public static String mergeAndSortChange(String str1, String str2) {
        //1.合并
        String str = str1 + str2;
        //2.排序
        ArrayList<Character> list1 = new ArrayList<>();//存放偶数位字符
        ArrayList<Character> list2 = new ArrayList<>();//存放奇数位字符
        for (int i = 0; i < str.length(); i++) {
            if (i % 2 == 0) {
                list1.add(str.charAt(i));
            } else {
                list2.add(str.charAt(i));
            }
        }
        Collections.sort(list1);
        Collections.sort(list2);
        //重新拼接
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < list1.size();i++) { //list1.size()>=list2.size()
                builder.append(list1.get(i));
                if(i<= list2.size()-1){ //防止越界
                    builder.append(list2.get(i));
                }
        }
        //3.对字符进行转换操作
        for (int i = 0; i < builder.length(); i++) {
            String s = builder.substring(i,i+1);
            if(s.matches("[0-9a-fA-F]")){
                //把16进制转成10进制，再转成二进制
                StringBuilder binary = new StringBuilder(Integer.toBinaryString(Integer.parseInt(s,16)));
                int len = binary.length();
                for (int j = 0; j <4-len ; j++) { //补零
                    binary.insert(0, "0");
                }
                binary = binary.reverse();//翻转
                int n = Integer.parseInt(binary.toString(), 2); //把二进制转成10进制
                String hexString = Integer.toHexString(n).toUpperCase();//转成16进制字符串大写
                builder.replace(i,i+1,hexString);//替换
            }
        }   
        return builder.toString();

    }

}