Faster String Matching/Iteration Method?

Question

In the program I'm currently working on, there's one part that's taking a bit long. Basically, I have a list of Strings and one target phrase. As an example, let's say the target phrase is "inventory of finished goods". Now, after filtering out the stop word (of), I want to extract all Strings from the list that contains one of the three words: "inventory", "finished", and "goods". Right now, I implemented the idea as follows:

String[] targetWords; // contains "inventory", "finished", and "goods"
ArrayList<String> extractedStrings = new ArrayList<String>();

for (int i = 0; i < listOfWords.size(); i++) {
    String[] words = listOfWords.get(i).split(" ");
    outerloop:
    for (int j = 0; j < words.length; j++) {
        for (int k = 0; k < targetWords.length; k++) {
            if (words[j].equalsIgnoreCase(targetWords[k])) {
                extractedStrings.add(listOfWords.get(i));
                break outerloop;
            }
        }
    }
}

The list contains over 100k words, and with this it takes rounghly .4 to .8 seconds to complete the task for each target phrase. The things is, I have a lot of these target phrases to process, and the seconds really add up. Thus, I was wondering if anyone knew of a more efficient way to complete this task? Thanks for the help in advance!

Answer 1

Your list of 100k words could be added (once) to a HashSet. Rather than iterating through your list, use wordSet.contains() - a HashSet gives constant-time performance for this, so not affected by the size of the list.

Answer 2

You can take your giant list of words and add them to a hash map and then when your phrase comes in, just loop over the words in your phrase and check against the hash map. Currently you are doing a linear search and what I'm proposing would cut it down to a constant time search.

The key is minimizing lookups. Using this technique you would be effectively indexing your giant list of words for fast lookups.