按长度存储和排序单词的最有效方法？

Question

Since many words might have the same length, an insertion operation to a certain database can be costly.

I saw the following suggestions for storing and sorting words by length. Which is the most efficient?

1. Key: length of word, Value: Set of all words with that length. Using HashMap: Sorting all words in a file by length, in one read. (Java)

2. Using Guava's MultiMap: https://stackoverflow.com/a/4244798/2653179

3. TreeMap? Or storing the words in an ArrayList, writing compare function, then using Collections.sort: Java: Sort a list of words by length, then by alphabetical order

Or other suggestions?

Answer 1

Most efficient way to store and sort words by length?

Map<Integer, List<String>> - map where the key is the word length and the value is a list with words

Answer 2

With using Guava you could create a multimap with keys sorted by a length:

TreeMultimap<Integer, String> map = TreeMultimap.create();

//as Java's map 
NavigableMap<Integer, Collection<String>> asMap = map.asMap();

Adding items:

for (String word : new String[]{"cd", "efg", "k", "a", "b", "ab"}) {
    map.put(word.length(), word);
}

System.out.println("words: " + map);

Prints:

words: {1=[a, b, k], 2=[ab, cd], 3=[efg]}