题解 | #字符串排序#

import java.util.*;
import java.util.stream.Stream;

// 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);
        while (in.hasNextLine()) {
            String str = in.nextLine();
            char[] chs = str.toCharArray();
            // 相同的字母分组存储，排序完成后，再按输入的顺序组装起来
            Map<String, List<Character>> iptChsMap = getIptSortChsMap(chs);
            // 对输入的字符进行排序，使用冒泡法
            sortWithIptStr(chs);
            // 按输入的顺序还原相同的字符
            recoverWithIptSort(chs, iptChsMap);
            // 输出
            StringBuilder sb = new StringBuilder();
            Stream.of(chs).forEach(sb::append);
            System.out.println(sb);
        }
    }

    private static void recoverWithIptSort(char[] chs,
                                           Map<String, List<Character>> iptChsMap) {
        for (int i = 0; i < chs.length; i++) {
            String lowerStr = String.valueOf(chs[i]).toLowerCase();
            List<Character> sameList = iptChsMap.get(lowerStr);
            if (sameList != null) {
                // 每次都取一个，拼接完删除
                char ch = sameList.remove(0);
                chs[i] = ch;
            }
        }
    }

    private static void sortWithIptStr(char[] chs) {
        char temp;
        for (int i = 0; i < chs.length - 1; i++) {
            for (int j = i; j < chs.length; j++) {
                if (isLetterChar(chs[i]) && isLetterChar(chs[j])) {
                    char preChar = String.valueOf(chs[i]).toLowerCase().toCharArray()[0];
                    char nextChar = String.valueOf(chs[j]).toLowerCase().toCharArray()[0];
                    if (preChar > nextChar) {
                        temp = chs[i];
                        chs[i] = chs[j];
                        chs[j] = temp;
                    }
                }
            }
        }
    }

    private static Map<String, List<Character>> getIptSortChsMap(char[] chs) {
        Map<String, List<Character>> iptChsMap = new HashMap<>();
        for (char ch : chs) {
            String lowerStr = String.valueOf(ch).toLowerCase();
            List<Character> sameList = iptChsMap.get(lowerStr);
            if (sameList == null) {
                sameList = new ArrayList<>();
                iptChsMap.put(lowerStr, sameList);
            }
            sameList.add(ch);
        }
        return iptChsMap;
    }

    private static boolean isLetterChar(char ch) {
        if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
            return true;
        }
        return false;
    }
}