字符串排序

• StringBuilder and Comparator, 简单地忽略大小写排个序即可

import java.util.*;

public class Main {

    public static String sort(String str) {
        // 先将英文字母收集起来
        List<Character> letters = new ArrayList<>();
        for (char ch : str.toCharArray()) {
            if (Character.isLetter(ch)) {
                letters.add(ch);
            }
        }
        // 将英文字母先排序好
        letters.sort(new Comparator<Character>() {
            public int compare(Character o1, Character o2) {
                return Character.toLowerCase(o1) - Character.toLowerCase(o2);
            }
        });
        // 若是非英文字母则直接添加
        StringBuilder result = new StringBuilder();
        for (int i = 0, j = 0; i < str.length(); i++) {
            if (Character.isLetter(str.charAt(i))) {
                result.append(letters.get(j++));
            }
            else {
                result.append(str.charAt(i));
            }
        }
        return result.toString();
    }

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