题解 | #字符串排序#

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextLine()) {
            String str = sc.nextLine();
            str = rule(str);
            System.out.println(str);
        }
    }

    private static String rule(String str) {
        List<Character> list = new ArrayList<>();
        for (int i = 0; i < str.length(); i++) {
            if (Character.isLetter(str.charAt(i))) {
                list.add(str.charAt(i));
            }
        }
        //规则1规则2的实现
        list.sort(new Comparator<Character>() {
            @Override
            public int compare(Character o1, Character o2) {
                return Character.toLowerCase(o1) - Character.toLowerCase(o2);
            }
        });
        //规则3
        StringBuilder sb = new StringBuilder();
        for (int i = 0, j = 0; i < str.length(); i++) {
            if(list.contains(str.charAt(i))){
                sb.append(list.get(j));
                j++;
            }else{
                sb.append(str.charAt(i));
            }
        }
        return sb.toString();
    }
}