题解 | #字符串排序#

import java.util.*; 
import java.io.*;

// 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) {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try {
            String s = br.readLine();
            char[] chars = s.toCharArray();
            ArrayList<Character> list = new ArrayList();
            for (char c : chars) {
                if (Character.isLetter(c)) {
                    list.add(c);
                }
            }
            list.sort(new Comparator<Character>() {
                @Override
                public int compare(Character o1, Character o2) {
                    return Character.toLowerCase(o1) - Character.toLowerCase(o2);
                }
            });
            StringBuffer stb = new StringBuffer();
            for (int i = 0, j = 0; i < s.length(); i++) {
                if (Character.isLetter(s.charAt(i))) {
                    stb.append(list.get(j++));
                } else {
                    stb.append(s.charAt(i));
                }
            }
            System.out.println(stb.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}