题解 | #字符串合并处理#

import java.util.*;

// 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 ssc = new Scanner(System.in);
        while (ssc.hasNext()) {
            String s1 = ssc.next();
            String s2 = ssc.next();
            //将字符串拼接起来
            String s = s1 + s2;
            List<Character> list1 = new ArrayList<>();
            List<Character> list2 = new ArrayList<>();
            for (int i = 0 ; i < s.length(); i++) {
                //偶数
                if (i % 2 == 0) {
                    list1.add(s.charAt(i));
                    continue;
                }
                //奇数
                if (i % 2 == 1) {
                    list2.add(s.charAt(i));
                }
            }
            Collections.sort(list1);
            Collections.sort(list2);
            StringBuilder sb = new StringBuilder();
            for (int i = 0, j = 0, k = 0; i < s.length(); i++) {
                if (i % 2 == 0) {
                    sb.append(list1.get(k));
                    k++;
                    continue;
                }
                if (i % 2 == 1) {
                    sb.append(list2.get(j));
                    j++;
                }
            }
            //完成第一步后，现在开始第二步
            Map<Character, Integer> map = new HashMap<>();
            map.put('a', 10);
            map.put('b', 11);
            map.put('c', 12);
            map.put('d', 13);
            map.put('e', 14);
            map.put('f', 15);
            map.put('A', 10);
            map.put('B', 11);
            map.put('C', 12);
            map.put('D', 13);
            map.put('E', 14);
            map.put('F', 15);
            String s3 = sb.toString();
            StringBuilder finalSb = new StringBuilder();
            for (int i = 0; i < s3.length(); i++) {
                //如果是数字
                if (Character.isDigit(s3.charAt(i))) {
                    int revBinary = isReverseBinary(s3.charAt(i));
                    finalSb.append(Integer.toString(revBinary, 16).toUpperCase());
                    continue;
                }
                if (Character.isLetter(s3.charAt(i))) {
                    if (map.containsKey(s3.charAt(i))) {
                        int repreBinary = isBinary(map.get(s3.charAt(i)));
                        finalSb.append(Integer.toString(repreBinary, 16).toUpperCase());
                        continue;
                    }
                }
                finalSb.append(s3.charAt(i));
            }
            System.out.println(finalSb.toString());
        }
    }

    private static int isReverseBinary(char x) {
        int tmp = x - '0';
        tmp = isBinary(tmp);
        return tmp;
    }

    private static int isBinary(int tmp) {
        StringBuilder sb = new StringBuilder();
        while (tmp > 0) {
            sb.append(tmp % 2);
            tmp /= 2;
        }
        while (sb.length() < 4) {
            sb.append(0);
        }
        return Integer.parseInt(sb.toString(), 2);
    }
}