题解 | #字符串合并处理#

import java.util.*;

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 = a.replaceAll(" ", "");
            char[] c = b.toCharArray();
            List<Character> odds = new ArrayList<>();
            List<Character> evens = new ArrayList<>();
            for (int i = 0; i < c.length; i++) {
                if (i % 2 == 0) {
                    odds.add(c[i]);
                } else {
                    evens.add(c[i]);
                }
            }
            evens.sort(Comparator.comparingInt(j -> j));
            odds.sort(Comparator.comparingInt(j -> j));
            for (int i = 0; i < c.length; i++) {
                if (i % 2 == 0) {
                    c[i] = odds.get(i / 2);
                } else {
                    c[i] = evens.get((i - 1) / 2);
                }
            }

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < c.length; i++) {
                StringBuilder sb0=new StringBuilder();
                if (String.valueOf(c[i]).matches("[A-Fa-f]")) {
                    String d = Integer.toBinaryString(Integer.parseInt(String.valueOf(c[i]), 16));
                    if (d.length()<4) {
                        sb0.append("0000",0,4-d.length());
                    }
                    String e = String.valueOf(sb0.append(d).reverse());
                    sb.append(Integer.toHexString(Integer.parseInt(e, 2)).toUpperCase());
                } else if (String.valueOf(c[i]).matches("[0-9]")) {
                    String d = Integer.toBinaryString(Integer.parseInt(String.valueOf(c[i])));
                    if (d.length()<4) {
                        sb0.append("0000",0,4-d.length());
                    }
                    String e = String.valueOf(sb0.append(d).reverse());
                    sb.append(Integer.toHexString(Integer.parseInt(e, 2)).toUpperCase());
                } else {
                    sb.append(c[i]);
                }
            }
            System.out.println(sb);
        }
    }
}