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 sc = new Scanner(System.in);
        String str1 = sc.next();
        String str2 = sc.next();
        String STR = str1 + str2;
        Sort(STR);
    }

    public static void Sort(String str) {

        String[] STR = str.split("");
        ArrayList<String> list1 = new ArrayList<>();
        ArrayList<String> list2 = new ArrayList<>();

        for (int i = 0; i < STR.length; i++) {
            if (i % 2 == 0) {
                list1.add(STR[i]);
            } else {
                list2.add(STR[i]);
            }
        }
        Collections.sort(list1);
        Collections.sort(list2);

        ArrayList<String> target = new ArrayList<>();
        for (int i = 0, j = 0, f = 0; i < str.length(); i++) {
            if (i % 2 == 0) {
                target.add(list1.get(j++));
            } else {
                target.add(list2.get(f++));
            }
        }
        ChangeStr(target);
    }

    public static void ChangeStr(ArrayList<String> target) {
        StringBuilder SB = new StringBuilder();
        for (String s : target) {
            if (s.matches("[a-f]||[A-F]")) {
                SB.append(Integer.toHexString(Integer.parseInt(new StringBuffer(
                                                  Integer.toBinaryString(Integer.parseInt(s, 16))).reverse().toString(),
                                              2)).toUpperCase());
            } else if (s.matches("[0-9]")) {

                SB.append(Integer.toHexString(Integer.parseInt(new StringBuffer("000" +
                                              Integer.toBinaryString(Integer.parseInt(s))).reverse().substring(0, 4),
                                              2)).toUpperCase());

            } else {
                SB.append(s);
            }
        }
        System.out.println(SB);
    }
}