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 str = sc.next();
            // 第一步：字符串合并
            str = str + sc.next();
            // 第二步：字符串奇偶排序
            int length = str.length();
            List<Character> even = new ArrayList<>();
            List<Character> odd = new ArrayList<>();
            for (int i = 0; i < length; i++) {
                if (i % 2 == 0) {
                    even.add(str.charAt(i));
                } else {
                    odd.add(str.charAt(i));
                }
            }
            Collections.sort(even);
            Collections.sort(odd);
            // 重新拼接
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < even.size(); i++) {
                sb.append(even.get(i));
                if (i < odd.size()) {
                    sb.append(odd.get(i));
                }
            }
            String sort = sb.toString();
            // 第三步：字符转换
            for (int i = 0; i < length; i++) {
                char c = sort.charAt(i);
                int decimal;
                if (Character.isDigit(c)) {
                    decimal = c - '0';
                } else if (Character.isLetter(c) && (Character.toUpperCase(c) - 'F' <= 0)) {
                    decimal = Character.toUpperCase(c) - 'A' + 10;
                } else {
                    System.out.print(c);
                    continue;
                }
                String binaryStr = Integer.toBinaryString(decimal);
                int initLength = binaryStr.length();
                if (binaryStr.length() < 4) {
                    for (int j = 0; j < 4 - initLength; j++) {
                        binaryStr = 0 + binaryStr;
                    }
                }
                String revertBinary = new StringBuilder(binaryStr).reverse().toString();
                String hexStr = Integer.toHexString(Integer.valueOf(revertBinary, 2)).toUpperCase(Locale.ROOT);
                System.out.print(hexStr);
            }
            System.out.println();
        }
        sc.close();
    }
}