java - 字符串基数排序 - StringIndexOutOfBoundsEception

Question

我正在编写自己的基数排序方法来对字符串中的单词进行排序(大黑猫坐在 beautiful brown mat 将被分类为 beautiful big black brown cat mat on sat the the)。该方法接收单个单词的 List(我自己的 List 接口(interface))并重新排列列表。

到目前为止，这是我的方法:

public static void stringRadixSort(List<String> list, int letters) {
    List<String>[] buckets = (List<String>[]) Array.newInstance(List.class, 26);

    int letterNumber = 1; //Sorts list by 1st letter of each word, then 2nd etc.
    for (int i = 0; i < letters; i++) {
        while (!list.isEmpty()) {
            String word = list.remove(list.first());
            if (word.length() > letters) throw new UnsortableException("The list contains a word that holds more letters than the given maximum number of letters."
                    + "\nMax Letters: " + letters + "\nWord: " + word);
            String letter = word.substring(letterNumber - 1, letterNumber); //EXCEPTION THROWN
            char ch = letter.charAt(0);
            int index = ch - 'a';    //gets index of each letter ('a' = buckets[0], 'z' = buckets[25]
            if (buckets[index] == null) {
                buckets[index] = new LinkedList<String>();
            }
            buckets[index].insertLast(word);
        }

        for (int j = 0; j < buckets.length; j++) {
            if (buckets[j] != null) {
                while (!buckets[j].isEmpty()) {
                    list.insertLast(buckets[j].remove(buckets[j].first()));
                }
            }
        }
        letterNumber++;
    }
}

我的方法的(唯一的，我希望的)问题是，当我读取单词的每个字符时，我创建了单词的单个字母子字符串。由于外部 for 循环运行了 letters 次(其中 letters 是 List 中单词的最大长度)，当此循环的迭代次数大于当前单词的长度 - 即 letterNumber > word.length() - 因此它尝试使用大于字符串长度的字符串索引创建子字符串.

如何调整我的方法，使其只创建每个单词的子字符串，直到 letterNumber == word.length()，然后才能将排序算法应用于这些较短的单词 - “a”将成为“aa”之前。

Answer 1

只需将比字符串长度短的元素分组到一个额外的组中。您还需要先对最不重要(相关)的字符进行排序。以下代码使用 java 集合而不是您使用的任何数据结构:

public static void stringRadixSort(List<String> list, int letters) {
    if (list.size() <= 1) {
        return;
    }

    List<String>[] buckets = new List[27];
    for (int i = 0; i < buckets.length; i++) {
        buckets[i] = new LinkedList<>();
    }
    int largestLength = -1;
    int secondLargestLength = 0;
    for (String s : list) {
        int length = s.length();
        if (length >= largestLength) {
            secondLargestLength = largestLength;
            largestLength = length;
        } else if (secondLargestLength < length) {
            secondLargestLength = length;
        }
    }

    if (largestLength > letters) {
        throw new IllegalArgumentException("one of the strings is too long");
    }

    for (int i = secondLargestLength == largestLength ? secondLargestLength-1 : secondLargestLength; i >= 0; i--) {
        for (String word : list) {
            int index = (word.length() <= i) ? 0 : word.charAt(i) - ('a' - 1);
            buckets[index].add(word);
        }

        list.clear();

        for (List<String> lst : buckets) {
            if (lst != null) {
                list.addAll(lst);
                lst.clear();
            }
        }
    }
}