题解 | 字符串排序

import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.TreeMap;

// 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 in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextLine()) { // 注意 while 处理多个 case
            // int a = in.nextInt();
            // int b = in.nextInt();
            // System.out.println(a + b);
            String s = in.nextLine();

            ArrayList<Character> list = new ArrayList<>();
            for (char c : s.toCharArray()) {
                if (Character.isLetter(c)) {
                    list.add(c);
                }
            }

            list.sort(Comparator.comparing(Character::toLowerCase));

            StringBuilder ret = new StringBuilder();
            for (int i=0,j=0;i<s.length();i++) {
                if (Character.isLetter(s.charAt(i))) {
                    ret.append(list.get(j++));
                } else {
                    ret.append(s.charAt(i));
                }
            }
            
            System.out.println(ret.toString());
        }
    }
}