Java Dictionary Searcher

Question

I am trying to implement a program that will take a users input, split that string into tokens, and then search a dictionary for the words in that string. My goal for the pa

Answer 1

Splitting the input string every possible way is not going to finish in a reasonable amount of time if you want to support 20 or more characters. Here's a more efficient approach, comments inline:

public static void main(String[] args) throws IOException {
    // load the dictionary into a set for fast lookups
    Set dictionary = new HashSet();
    Scanner filescan = new Scanner(new File("dictionary.txt"));
    while (filescan.hasNext()) {
        dictionary.add(filescan.nextLine().toLowerCase());
    }

    // scan for input
    Scanner scan = new Scanner(System.in);
    System.out.print("Enter a string: ");
    String input = scan.next().toLowerCase();
    System.out.println();

    // place to store list of results, each result is a list of strings
    List> results = new ArrayList<>();

    long time = System.currentTimeMillis();

    // start the search, pass empty stack to represent words found so far
    search(input, dictionary, new Stack(), results);

    time = System.currentTimeMillis() - time;

    // list the results found
    for (List result : results) {
        for (String word : result) {
            System.out.print(word + " ");
        }
        System.out.println("(" + result.size() + " words)");
    }
    System.out.println();
    System.out.println("Took " + time + "ms");
}

public static void search(String input, Set dictionary,
        Stack words, List> results) {

    for (int i = 0; i < input.length(); i++) {
        // take the first i characters of the input and see if it is a word
        String substring = input.substring(0, i + 1);

        if (dictionary.contains(substring)) {
            // the beginning of the input matches a word, store on stack
            words.push(substring);

            if (i == input.length() - 1) {
                // there's no input left, copy the words stack to results
                results.add(new ArrayList(words));
            } else {
                // there's more input left, search the remaining part
                search(input.substring(i + 1), dictionary, words, results);
            }

            // pop the matched word back off so we can move onto the next i
            words.pop();
        }
    }
}

Example output:

Enter a string: aman

a man (2 words)
am an (2 words)

Took 0ms

Here's a much longer input:

Enter a string: thequickbrownfoxjumpedoverthelazydog

the quick brown fox jump ed over the lazy dog (10 words)
the quick brown fox jump ed overt he lazy dog (10 words)
the quick brown fox jumped over the lazy dog (9 words)
the quick brown fox jumped overt he lazy dog (9 words)

Took 1ms